CMP Journal 2025-01-29
Statistics
Nature: 20
Nature Materials: 2
Nature Reviews Materials: 1
Physical Review Letters: 6
Physical Review X: 2
arXiv: 64
Nature
Molecular basis of vitamin K driven γ-carboxylation at membrane interface
Original Paper | Cryoelectron microscopy | 2025-01-28 19:00 EST
Qing Cao, Aaron Ammerman, Mierxiati Saimi, Zongtao Lin, Guomin Shen, Huaping Chen, Jie Sun, Mengqi Chai, Shixuan Liu, Fong-Fu Hsu, Andrzej M. Krezel, Michael L. Gross, Jinbin Xu, Benjamin A. Garcia, Bin Liu, Weikai Li
The γ-carboxylation of glutamate residues enables Ca2+-mediated membrane assembly of protein complexes that support broad physiological functions including hemostasis, calcium homeostasis, immune response, and endocrine regulation1-4. Modulating γ-carboxylation level provides prevalent treatments for hemorrhagic and thromboembolic diseases5. This unique posttranslational modification requires vitamin K hydroquinone (KH2) to drive highly demanding reactions6 catalyzed by the membrane-integrated γ-carboxylase (VKGC). To decipher underlying mechanisms, we determined cryo-electron microscopy structures of human VKGC in unbound form, with KH2 and four hemostatic and non-hemostatic proteins possessing propeptides and glutamate-rich domains in different carboxylation states. VKGC recognizes substrate proteins via knob-and-hole interactions with propeptides, thereby bringing tethered glutamate-containing segments for processive carboxylation within a large chamber that provides steric control. Propeptide binding also triggers a global conformational change to signal VKGC activation. Through sequential deprotonation and KH2 epoxidation, VKGC generates free hydroxide ion as an exceptionally strong base required to deprotonate the γ-carbon of glutamate for CO2 addition. The diffusion of this superbase, protected and guided by a sealed hydrophobic tunnel, elegantly resolves the challenge of coupling KH2 epoxidation to γ-carboxylation across the membrane interface. These structural insights and extensive functional experiments advance membrane enzymology and propel the development of novel treatments for γ-carboxylation disorders.
Cryoelectron microscopy, Enzyme mechanisms, Mechanisms of disease, Physiology, Post-translational modifications
Engineered heart muscle allografts for heart repair in primates and humans
Original Paper | Preclinical research | 2025-01-28 19:00 EST
Ahmad-Fawad Jebran, Tim Seidler, Malte Tiburcy, Maria Daskalaki, Ingo Kutschka, Buntaro Fujita, Stephan Ensminger, Felix Bremmer, Amir Moussavi, Huaxiao Yang, Xulei Qin, Sophie Mißbach, Charis Drummer, Hassina Baraki, Susann Boretius, Christopher Hasenauer, Tobias Nette, Johannes Kowallick, Christian O. Ritter, Joachim Lotz, Michael Didié, Mathias Mietsch, Tim Meyer, George Kensah, Dennis Krüger, Md Sadman Sakib, Lalit Kaurani, Andre Fischer, Ralf Dressel, Ignacio Rodriguez-Polo, Michael Stauske, Sebastian Diecke, Kerstin Maetz-Rensing, Eva Gruber-Dujardin, Martina Bleyer, Beatrix Petersen, Christian Roos, Liye Zhang, Lutz Walter, Silke Kaulfuß, Gökhan Yigit, Bernd Wollnik, Elif Levent, Berit Roshani, Christiane Stahl-Henning, Philipp Ströbel, Tobias Legler, Joachim Riggert, Kristian Hellenkamp, Jens-Uwe Voigt, Gerd Hasenfuß, Rabea Hinkel, Joseph C. Wu, Rüdiger Behr, Wolfram-Hubertus Zimmermann
Cardiomyocytes can be implanted to remuscularize the failing heart1,2,3,4,5,6,7. Challenges include sufficient cardiomyocyte retention for a sustainable therapeutic impact without intolerable side effects, such as arrhythmia and tumour growth. We investigated the hypothesis that epicardial engineered heart muscle (EHM) allografts from induced pluripotent stem cell-derived cardiomyocytes and stromal cells structurally and functionally remuscularize the chronically failing heart without limiting side effects in rhesus macaques. After confirmation of in vitro and in vivo (nude rat model) equivalence of the newly developed rhesus macaque EHM model with a previously established Good Manufacturing Practice-compatible human EHM formulation8, long-term retention (up to 6 months) and dose-dependent enhancement of the target heart wall by EHM grafts constructed from 40 to 200 million cardiomyocytes/stromal cells were demonstrated in macaques with and without myocardial infarction-induced heart failure. In the heart failure model, evidence for EHM allograft-enhanced target heart wall contractility and ejection fraction, which are measures for local and global heart support, was obtained. Histopathological and gadolinium-based perfusion magnetic resonance imaging analyses confirmed cell retention and functional vascularization. Arrhythmia and tumour growth were not observed. The obtained feasibility, safety and efficacy data provided the pivotal underpinnings for the approval of a first-in-human clinical trial on tissue-engineered heart repair. Our clinical data confirmed remuscularization by EHM implantation in a patient with advanced heart failure.
Preclinical research, Regeneration, Stem-cell research, Tissue engineering, Translational research
Methanol transfer supports metabolic syntrophy between bacteria and archaea
Original Paper | Archaeal physiology | 2025-01-28 19:00 EST
Yan Huang, Kensuke Igarashi, Laiyan Liu, Daisuke Mayumi, Tomomi Ujiie, Lin Fu, Min Yang, Yahai Lu, Lei Cheng, Souichiro Kato, Masaru K. Nobu
In subsurface methanogenic ecosystems, the ubiquity of methylated-compound-using archaea--methylotrophic methanogens1,2,3,4--implies that methylated compounds have an important role in the ecology and carbon cycling of such habitats. However, the origin of these chemicals remains unclear5,6 as there are no known energy metabolisms that generate methylated compounds de novo as a major product. Here we identified an energy metabolism in the subsurface-derived thermophilic anaerobe Zhaonella formicivorans7 that catalyses the conversion of formate to methanol, thereby producing methanol without requiring methylated compounds as an input. Cultivation experiments showed that formate-driven methanologenesis is inhibited by the accumulation of methanol. However, this limitation can be overcome through methanol consumption by a methylotrophic partner methanogen, Methermicoccus shengliensis. This symbiosis represents a fourth mode of mutualistic cross-feeding driven by thermodynamic necessity (syntrophy), previously thought to rely on transfer of hydrogen, formate or electrons8,9,10. The unusual metabolism and syntrophy provide insights into the enigmatic presence of methylated compounds in subsurface methanogenic ecosystems and demonstrate how organisms survive at the thermodynamic limit through metabolic symbiosis.
Archaeal physiology, Bacterial physiology, Environmental microbiology, Microbial ecology
SARS-CoV-2 evolution on a dynamic immune landscape
Original Paper | Data integration | 2025-01-28 19:00 EST
N. Alexia Raharinirina, Nils Gubela, Daniela Börnigen, Maureen Rebecca Smith, Djin-Ye Oh, Matthias Budt, Christin Mache, Claudia Schillings, Stephan Fuchs, Ralf Dürrwald, Thorsten Wolff, Martin Hölzer, Sofia Paraskevopoulou, Max von Kleist
Since the onset of the pandemic, many SARS-CoV-2 variants have emerged, exhibiting substantial evolution in the virus' spike protein1, the main target of neutralizing antibodies2. A plausible hypothesis proposes that the virus evolves to evade antibody-mediated neutralization (vaccine- or infection-induced) to maximize its ability to infect an immunologically experienced population1,3. Because viral infection induces neutralizing antibodies, viral evolution may thus navigate on a dynamic immune landscape that is shaped by local infection history. Here we developed a comprehensive mechanistic model, incorporating deep mutational scanning data4,5, antibody pharmacokinetics and regional genomic surveillance data, to predict the variant-specific relative number of susceptible individuals over time. We show that this quantity precisely matched historical variant dynamics, predicted future variant dynamics and explained global differences in variant dynamics. Our work strongly suggests that the ongoing pandemic continues to shape variant-specific population immunity, which determines a variant's ability to transmit, thus defining variant fitness. The model can be applied to any region by utilizing local genomic surveillance data, allows contextualizing risk assessment of variants and provides information for vaccine design.
Data integration, Epidemiology, Viral infection
Structure and mechanism of vitamin-K-dependent γ-glutamyl carboxylase
Original Paper | Cryoelectron microscopy | 2025-01-28 19:00 EST
Rong Wang, Baozhi Chen, Nadia Elghobashi-Meinhardt, Jian-Ke Tie, Alyssa Ayala, Ning Zhou, Xiaofeng Qi
γ-Glutamyl carboxylase (GGCX) is the sole identified enzyme that uses vitamin K (VK) as a cofactor in humans. This protein catalyses the oxidation of VK hydroquinone to convert specific glutamate residues to γ-carboxyglutamate residues in VK-dependent proteins (VDPs), which are involved in various essential biological processes and diseases1,2,3. However, the working mechanism of GGCX remains unclear. Here we report three cryogenic electron microscopy structures of human GGCX: in the apo state, bound to osteocalcin (a VDP) and bound to VK. The propeptide of the VDP binds to the lumenal domain of GGCX, which stabilizes transmembrane helices 6 and 7 of GGCX to create the VK-binding pocket. After binding of VK, residue Lys218 in GGCX mediates the oxidation of VK hydroxyquinone, which leads to the deprotonation of glutamate residues and the construction of γ-carboxyglutamate residues. Our structural observations and results from binding and cell biological assays and molecular dynamics simulations show that a cholesterol molecule interacts with the transmembrane helices of GGCX to regulate its protein levels in cells. Together, these results establish a link between cholesterol metabolism and VK-dependent pathways.
Cryoelectron microscopy, Enzyme mechanisms, Oxidoreductases, Sterols, Target validation
Warming and cooling catalyse widespread temporal turnover in biodiversity
Original Paper | Biodiversity | 2025-01-28 19:00 EST
Malin L. Pinsky, Helmut Hillebrand, Jonathan M. Chase, Laura H. Antão, Myriam R. Hirt, Ulrich Brose, Michael T. Burrows, Benoit Gauzens, Benjamin Rosenbaum, Shane A. Blowes
Turnover in species composition through time is a dominant form of biodiversity change, which has profound effects on the functioning of ecological communities1,2,3,4. Turnover rates differ markedly among communities4, but the drivers of this variation across taxa and realms remain unknown. Here we analyse 42,225 time series of species composition from marine, terrestrial and freshwater assemblages, and show that temporal rates of turnover were consistently faster in locations that experienced faster temperature change, including both warming and cooling. In addition, assemblages with limited access to microclimate refugia or that faced stronger human impacts on land were especially responsive to temperature change, with up to 48% of species replaced per decade. These results reveal a widespread signal of vulnerability to continuing climate change and highlight which ecological communities are most sensitive, raising concerns about ecosystem integrity as climate change and other human impacts accelerate.
Biodiversity, Climate-change ecology, Community ecology
C-terminal amides mark proteins for degradation via SCF-FBXO31
Original Paper | Genetic engineering | 2025-01-28 19:00 EST
Matthias F. Muhar, Jakob Farnung, Martina Cernakova, Raphael Hofmann, Lukas T. Henneberg, Moritz M. Pfleiderer, Annina Denoth-Lippuner, Filip Kalčic, Ajse S. Nievergelt, Marwa Peters Al-Bayati, Nikolaos D. Sidiropoulos, Viola Beier, Matthias Mann, Sebastian Jessberger, Martin Jinek, Brenda A. Schulman, Jeffrey W. Bode, Jacob E. Corn
During normal cellular homeostasis, unfolded and mislocalized proteins are recognized and removed, preventing the build-up of toxic byproducts1. When protein homeostasis is perturbed during ageing, neurodegeneration or cellular stress, proteins can accumulate several forms of chemical damage through reactive metabolites2,3. Such modifications have been proposed to trigger the selective removal of chemically marked proteins3,4,5,6; however, identifying modifications that are sufficient to induce protein degradation has remained challenging. Here, using a semi-synthetic chemical biology approach coupled to cellular assays, we found that C-terminal amide-bearing proteins (CTAPs) are rapidly cleared from human cells. A CRISPR screen identified FBXO31 as a reader of C-terminal amides. FBXO31 is a substrate receptor for the SKP1-CUL1-F-box protein (SCF) ubiquitin ligase SCF-FBXO31, which ubiquitylates CTAPs for subsequent proteasomal degradation. A conserved binding pocket enables FBXO31 to bind to almost any C-terminal peptide bearing an amide while retaining exquisite selectivity over non-modified clients. This mechanism facilitates binding and turnover of endogenous CTAPs that are formed after oxidative stress. A dominant human mutation found in neurodevelopmental disorders reverses CTAP recognition, such that non-amidated neosubstrates are now degraded and FBXO31 becomes markedly toxic. We propose that CTAPs may represent the vanguard of a largely unexplored class of modified amino acid degrons that could provide a general strategy for selective yet broad surveillance of chemically damaged proteins.
Genetic engineering, High-throughput screening, Post-translational modifications, Proteomics, Ubiquitylation
Copper-dependent halogenase catalyses unactivated C-H bond functionalization
Original Paper | Biocatalysis | 2025-01-28 19:00 EST
Chen-Yu Chiang, Masao Ohashi, Jessie Le, Pan-Pan Chen, Qingyang Zhou, Songrong Qu, Undramaa Bat-Erdene, Shabnam Hematian, Jose A. Rodriguez, K. N. Houk, Yisong Guo, Joseph A. Loo, Yi Tang
Carbon-hydrogen (C-H) bonds are the foundation of essentially every organic molecule, making them an ideal place to do chemical synthesis. The key challenge is achieving selectivity for one particular C(sp3)-H bond1,2,3. In recent years, metalloenzymes have been found to perform C(sp3)-H bond functionalization4,5. Despite substantial progresses in the past two decades6,7, enzymatic halogenation and pseudohalogenation of unactivated C(sp3)-H--providing a functional handle for further modification--have been achieved with only non-haem iron/α-ketoglutarate-dependent halogenases, and are therefore limited by the chemistry possible with these enzymes8. Here we report the discovery and characterization of a previously unknown halogenase ApnU, part of a protein family containing domain of unknown function 3328 (DUF3328). ApnU uses copper in its active site to catalyse iterative chlorinations on multiple unactivated C(sp3)-H bonds. By taking advantage of the softer copper centre, we demonstrate that ApnU can catalyse unprecedented enzymatic C(sp3)-H bond functionalization such as iodination and thiocyanation. Using biochemical characterization and proteomics analysis, we identified the functional oligomeric state of ApnU as a covalently linked homodimer, which contains three essential pairs--one interchain and two intrachain--of disulfide bonds. The metal-coordination active site in ApnU consists of binuclear type II copper centres, as revealed by electron paramagnetic resonance spectroscopy. This discovery expands the enzymatic capability of C(sp3)-H halogenases and provides a foundational understanding of this family of binuclear copper-dependent oxidative enzymes.
Biocatalysis, Biosynthesis, Enzymes
Signatures of longitudinal spin pumping in a magnetic phase transition
Original Paper | Spintronics | 2025-01-28 19:00 EST
Taekhyeon Lee, Min Tae Park, Hye-Won Ko, Jung Hyun Oh, San Ko, Seongmun Hwang, Jae Gwang Jang, Geon-Woo Baek, Se Kwon Kim, Hyun-Woo Lee, Myung-Hwa Jung, Kab-Jin Kim, Kyung-Jin Lee
A particle current generated by pumping in the absence of gradients in potential energy, density or temperature1 is associated with non-trivial dynamics. A representative example is charge pumping that is associated with the quantum Hall effect2 and the quantum anomalous Hall effect3. Spin pumping, the spin equivalent of charge pumping, refers to the emission of a spin current by magnetization dynamics4,5,6,7. Previous studies have focused solely on transversal spin pumping arising from classical dynamics, which corresponds to precessing atomic moments with constant magnitude. However, longitudinal spin pumping arising from quantum fluctuations, which correspond to a temporal change in the atomic moment's magnitude, remains unexplored. Here we experimentally investigate longitudinal spin pumping using iron-rhodium (FeRh), which undergoes a first-order antiferromagnet-to-ferromagnet phase transition during which the atomic moment's magnitude varies over time. By injecting a charge current into a FeRh/platinum bilayer, we induce a rapid phase transition of FeRh in nanoseconds, leading to the emission of a spin current to the platinum layer. The observed inverse spin Hall signal is about one order of magnitude larger than expected for transversal spin pumping, suggesting the presence of longitudinal spin pumping driven by quantum fluctuations and indicating its superiority over classical transversal spin pumping. Our result highlights the significance of quantum fluctuations in spin pumping and holds broad applicability in diverse angular momentum dynamics, such as laser-induced ultrafast demagnetization8, orbital pumping9,10 and quantum spin transfer11,12,13.
Spintronics
Degradable thermosets via orthogonal polymerizations of a single monomer
Original Paper | Polymer characterization | 2025-01-28 19:00 EST
Reagan J. Dreiling, Kathleen Huynh, Brett P. Fors
Crosslinked thermosets are highly durable materials, but overcoming their petrochemical origins and inability to be recycled poses a grand challenge1,2,3. Many strategies to access crosslinked polymers that are bioderived or degradable-by-design have been proposed, but they require several resource-intensive synthesis and purification steps and are not yet feasible alternatives to conventional consumer materials4,5,6,7,8. Here we present a modular, one-pot synthesis of degradable thermosets from the commercially available, biosourced monomer 2,3-dihydrofuran (DHF)9. In the presence of a ruthenium catalyst and photoacid generator, DHF undergoes slow ring-opening metathesis polymerization to give a soft polymer; then, exposure to light triggers strong acid generation and promotes the cationic polymerization of the same DHF monomer to spatially crosslink and strengthen the material10,11,12. By manipulating catalyst loading and light exposure, we can access materials with physical properties spanning orders of magnitude and achieve spatially resolved material domains. Importantly, the DHF-based thermosets undergo stimuli-selective degradation and can be recycled to the monomer under mild heating. The use of two distinct polymerization mechanisms on a single functional group allows the synthesis of degradable and recyclable thermoset materials with precisely controlled properties.
Polymer characterization, Polymer synthesis
Maize monoculture supported pre-Columbian urbanism in southwestern Amazonia
Original Paper | Archaeology | 2025-01-28 19:00 EST
Umberto Lombardo, Lautaro Hilbert, McKenzie Bentley, Christopher Bronk Ramsey, Kate Dudgeon, Albert Gaitan-Roca, José Iriarte, Andrés G. Mejía Ramón, Sergio Quezada, Marco Raczka, Jennifer G. Watling, Eduardo Neves, Francis Mayle
The Casarabe culture (500-1400 ce), spreading over roughly 4,500 km2 of the monumental mounds region of the Llanos de Moxos, Bolivia, is one of the clearest examples of urbanism in pre-Columbian (pre-1492 ce) Amazonia. It exhibits a four-tier hierarchical settlement pattern, with hundreds of monumental mounds interconnected by canals and causeways1,2. Despite archaeological evidence indicating that maize was cultivated by this society3, it is unknown whether it was the staple crop and which type of agricultural farming system was used to support this urban-scale society. Here, we address this issue by integration of remote sensing, field survey and microbotanical analyses, which shows that the Casarabe culture invested heavily in landscape engineering, constructing a complex system of drainage canals (to drain excess water during the rainy season) and newly documented savannah farm ponds (to retain water in the dry season). Phytolith analyses of 178 samples from 18 soil profiles in drained fields, farm ponds and forested settings record the singular and ubiquitous presence of maize (Zea mays) in pre-Columbian fields and farm ponds, and an absence of evidence for agricultural practices in the forest. Collectively, our findings show how the Casarabe culture managed the savannah landscape for intensive year-round maize monoculture that probably sustained its relatively large population. Our results have implications for how we conceive agricultural systems in Amazonia, and show an example of a Neolithic-like, grain-based agrarian economy in the Amazon.
Archaeology, Ecology
Contrasting drought sensitivity of Eurasian and North American grasslands
Original Paper | Community ecology | 2025-01-28 19:00 EST
Qiang Yu, Chong Xu, Honghui Wu, Yuguang Ke, Xiaoan Zuo, Wentao Luo, Haiyan Ren, Qian Gu, Hongqiang Wang, Wang Ma, Alan K. Knapp, Scott L. Collins, Jennifer A. Rudgers, Yiqi Luo, Yann Hautier, Chengjie Wang, Zhengwen Wang, Yong Jiang, Guodong Han, Yingzhi Gao, Nianpeng He, Juntao Zhu, Shikui Dong, Xiaoping Xin, Guirui Yu, Melinda D. Smith, Linghao Li, Xingguo Han
Extreme droughts generally decrease productivity in grassland ecosystems1,2,3 with negative consequences for nature's contribution to people4,5,6,7. The extent to which this negative effect varies among grassland types and over time in response to multi-year extreme drought remains unclear. Here, using a coordinated distributed experiment that simulated four years of growing-season drought (around 66% rainfall reduction), we compared drought sensitivity within and among six representative grasslands spanning broad precipitation gradients in each of Eurasia and North America--two of the Northern Hemisphere's largest grass-dominated regions. Aboveground plant production declined substantially with drought in the Eurasian grasslands and the effects accumulated over time, while the declines were less severe and more muted over time in the North American grasslands. Drought effects on species richness shifted from positive to negative in Eurasia, but from negative to positive in North America over time. The differing responses of plant production in these grasslands were accompanied by less common (subordinate) plant species declining in Eurasian grasslands but increasing in North American grasslands. Our findings demonstrate the high production sensitivity of Eurasian compared with North American grasslands to extreme drought (43.6% versus 25.2% reduction), and the key role of subordinate species in determining impacts of extreme drought on grassland productivity.
Community ecology, Ecosystem ecology
Bat genomes illuminate adaptations to viral tolerance and disease resistance
Original Paper | Comparative genomics | 2025-01-28 19:00 EST
Ariadna E. Morales, Yue Dong, Thomas Brown, Kaushal Baid, Dimitrios - Georgios Kontopoulos, Victoria Gonzalez, Zixia Huang, Alexis-Walid Ahmed, Arkadeb Bhuinya, Leon Hilgers, Sylke Winkler, Graham Hughes, Xiaomeng Li, Ping Lu, Yixin Yang, Bogdan M. Kirilenko, Paolo Devanna, Tanya M. Lama, Yomiran Nissan, Martin Pippel, Liliana M. Dávalos, Sonja C. Vernes, Sebastien J. Puechmaille, Stephen J. Rossiter, Yossi Yovel, Joseph B. Prescott, Andreas Kurth, David A. Ray, Burton K. Lim, Eugene Myers, Emma C. Teeling, Arinjay Banerjee, Aaron T. Irving, Michael Hiller
Zoonoses are infectious diseases transmitted from animals to humans. Bats have been suggested to harbour more zoonotic viruses than any other mammalian order1. Infections in bats are largely asymptomatic2,3, indicating limited tissue-damaging inflammation and immunopathology. To investigate the genomic basis of disease resistance, the Bat1K project generated reference-quality genomes of ten bat species, including potential viral reservoirs. Here we describe a systematic analysis covering 115 mammalian genomes that revealed that signatures of selection in immune genes are more prevalent in bats than in other mammalian orders. We found an excess of immune gene adaptations in the ancestral chiropteran branch and in many descending bat lineages, highlighting viral entry and detection factors, and regulators of antiviral and inflammatory responses. ISG15, which is an antiviral gene contributing to hyperinflammation during COVID-19 (refs. 4,5), exhibits key residue changes in rhinolophid and hipposiderid bats. Cellular infection experiments show species-specific antiviral differences and an essential role of protein conjugation in antiviral function of bat ISG15, separate from its role in secretion and inflammation in humans. Furthermore, in contrast to humans, ISG15 in most rhinolophid and hipposiderid bats has strong anti-SARS-CoV-2 activity. Our work reveals molecular mechanisms that contribute to viral tolerance and disease resistance in bats.
Comparative genomics, Evolutionary biology, Evolutionary genetics, Infection
Expanding the human gut microbiome atlas of Africa
Original Paper | Microbial ecology | 2025-01-28 19:00 EST
Dylan G. Maghini, Ovokeraye H. Oduaran, Luicer A. Ingasia Olubayo, Jane A. Cook, Natalie Smyth, Theophilous Mathema, Carl W. Belger, Godfred Agongo, Palwendé R. Boua, Solomon S. R. Choma, F. Xavier Gómez-Olivé, Isaac Kisiangani, Given R. Mashaba, Lisa Micklesfield, Shukri F. Mohamed, Engelbert A. Nonterah, Shane Norris, Hermann Sorgho, Stephen Tollman, Floidy Wafawanaka, Furahini Tluway, Michèle Ramsay, Jakob Wirbel, Ami S. Bhatt, Scott Hazelhurst
Population studies provide insights into the interplay between the gut microbiome and geographical, lifestyle, genetic and environmental factors. However, low- and middle-income countries, in which approximately 84% of the world's population lives1, are not equitably represented in large-scale gut microbiome research2,3,4. Here we present the AWI-Gen 2 Microbiome Project, a cross-sectional gut microbiome study sampling 1,801 women from Burkina Faso, Ghana, Kenya and South Africa. By engaging with communities that range from rural and horticultural to post-industrial and urban informal settlements, we capture a far greater breadth of the world's population diversity. Using shotgun metagenomic sequencing, we identify taxa with geographic and lifestyle associations, including Treponema and Cryptobacteroides species loss and Bifidobacterium species gain in urban populations. We uncover 1,005 bacterial metagenome-assembled genomes, and we identify antibiotic susceptibility as a factor that might drive Treponema succinifaciens absence in urban populations. Finally, we find an HIV infection signature defined by several taxa not previously associated with HIV, including Dysosmobacter welbionis and Enterocloster sp. This study represents the largest population-representative survey of gut metagenomes of African individuals so far, and paired with extensive clinical biomarkers and demographic data, provides extensive opportunity for microbiome-related discovery.
Microbial ecology, Microbiome
An evaporite sequence from ancient brine recorded in Bennu samples
Original Paper | Asteroids, comets and Kuiper belt | 2025-01-28 19:00 EST
T. J. McCoy, S. S. Russell, T. J. Zega, K. L. Thomas-Keprta, S. A. Singerling, F. E. Brenker, N. E. Timms, W. D. A. Rickard, J. J. Barnes, G. Libourel, S. Ray, C. M. Corrigan, P. Haenecour, Z. Gainsforth, G. Dominguez, A. J. King, L. P. Keller, M. S. Thompson, S. A. Sandford, R. H. Jones, H. Yurimoto, K. Righter, S. A. Eckley, P. A. Bland, M. A. Marcus, D. N. DellaGiustina, T. R. Ireland, N. V. Almeida, C. S. Harrison, H. C. Bates, P. F. Schofield, L. B. Seifert, N. Sakamoto, N. Kawasaki, F. Jourdan, S. M. Reddy, D. W. Saxey, I. J. Ong, B. S. Prince, K. Ishimaru, L. R. Smith, M. C. Benner, N. A. Kerrison, M. Portail, V. Guigoz, P.-M. Zanetta, L. R. Wardell, T. Gooding, T. R. Rose, T. Salge, L. Le, V. M. Tu, Z. Zeszut, C. Mayers, X. Sun, D. H. Hill, N. G. Lunning, V. E. Hamilton, D. P. Glavin, J. P. Dworkin, H. H. Kaplan, I. A. Franchi, K. T. Tait, S. Tachibana, H. C. Connolly Jr., D. S. Lauretta
Evaporation or freezing of water-rich fluids with dilute concentrations of dissolved salts can produce brines, as observed in closed basins on Earth1 and detected by remote sensing on icy bodies in the outer Solar System2,3. The mineralogical evolution of these brines is well understood in regard to terrestrial environments4, but poorly constrained for extraterrestrial systems owing to a lack of direct sampling. Here we report the occurrence of salt minerals in samples of the asteroid (101955) Bennu returned by the OSIRIS-REx mission5. These include sodium-bearing phosphates and sodium-rich carbonates, sulfates, chlorides and fluorides formed during evaporation of a late-stage brine that existed early in the history of Bennu's parent body. Discovery of diverse salts would not be possible without mission sample return and careful curation and storage, because these decompose with prolonged exposure to Earth's atmosphere. Similar brines probably still occur in the interior of icy bodies Ceres and Enceladus, as indicated by spectra or measurement of sodium carbonate on the surface or in plumes2,3.
Asteroids, comets and Kuiper belt, Astrobiology, Early solar system, Mineralogy, Petrology
The Ronne Ice Shelf survived the last interglacial
Original Paper | Cryospheric science | 2025-01-28 19:00 EST
Eric W. Wolff, Robert Mulvaney, Mackenzie M. Grieman, Helene M. Hoffmann, Jack Humby, Christoph Nehrbass-Ahles, Rachael H. Rhodes, Isobel F. Rowell, Louise C. Sime, Hubertus Fischer, Thomas F. Stocker, Amaelle Landais, Frédéric Parrenin, Eric J. Steig, Marina Dütsch, Nicholas R. Golledge
The fate of the West Antarctic Ice Sheet (WAIS)1 is the largest cause of uncertainty in long-term sea-level projections. In the last interglacial (LIG) around 125,000 years ago, data suggest that sea level was several metres higher than today2,3,4, and required a significant contribution from Antarctic ice loss, with WAIS usually implicated. Antarctica and the Southern Ocean were warmer than today5,6,7,8, by amounts comparable to those expected by 2100 under moderate to high future warming scenarios. However, direct evidence about the size of WAIS in the LIG is sparse. Here we use sea salt data from an ice core from Skytrain Ice Rise, adjacent to WAIS, to show that, during most of the LIG, the Ronne Ice Shelf was still in place, and close to its current extent. Water isotope data are consistent with a retreat of WAIS9, but seem inconsistent with more dramatic model realizations10 in which both WAIS and the large Antarctic ice shelves were lost. This new constraint calls for a reappraisal of other elements of the LIG sea-level budget. It also weakens the observational basis that motivated model simulations projecting the highest end of projections for future rates of sea-level rise to 2300 and beyond.
Cryospheric science, Palaeoclimate
CARD domains mediate anti-phage defence in bacterial gasdermin systems
Original Paper | Bacteria | 2025-01-28 19:00 EST
Tanita Wein, Adi Millman, Katharina Lange, Erez Yirmiya, Romi Hadary, Jeremy Garb, Sarah Melamed, Gil Amitai, Orly Dym, Felix Steinruecke, Aidan B. Hill, Philip J. Kranzusch, Rotem Sorek
Caspase recruitment domains (CARDs) and pyrin domains are important facilitators of inflammasome activity and pyroptosis1. Following pathogen recognition by nucleotide binding-domain, leucine-rich, repeat-containing (NLR) proteins, CARDs recruit and activate caspases, which, in turn, activate gasdermin pore-forming proteins to induce pyroptotic cell death2. Here we show that CARD domains are present in defence systems that protect bacteria against phage. The bacterial CARD domain is essential for protease-mediated activation of certain bacterial gasdermins, which promote cell death once phage infection is recognized. We further show that multiple anti-phage defence systems use CARD domains to activate a variety of cell death effectors, and that CARD domains mediate protein-protein interactions in these systems. We find that these systems are triggered by a conserved immune-evasion protein used by phages to overcome the bacterial defence system RexAB3, demonstrating that phage proteins inhibiting one defence system can activate another. Our results suggest that CARD domains represent an ancient component of innate immune systems conserved from bacteria to humans, and that CARD-dependent activation of gasdermins is shared in organisms across the tree of life.
Bacteria, Bacteriophages, Microbial genetics
Fine-tuning gibberellin improves rice alkali-thermal tolerance and yield
Original Paper | Abiotic | 2025-01-28 19:00 EST
Shuang-Qin Guo, Ya-Xin Chen, Ya-Lin Ju, Chen-Yang Pan, Jun-Xiang Shan, Wang-Wei Ye, Nai-Qian Dong, Yi Kan, Yi-Bing Yang, Huai-Yu Zhao, Hong-Xiao Yu, Zi-Qi Lu, Jie-Jie Lei, Ben Liao, Xiao-Rui Mu, Ying-Jie Cao, Liangxing Guo, Jin Gao, Ji-Fu Zhou, Kai-Yang Yang, Hong-Xuan Lin, Youshun Lin
Soil alkalinization and global warming are predicted to pose major challenges to agriculture in the future, as they continue to accelerate, markedly reducing global arable land and crop yields1,2. Therefore, strategies for future agriculture are needed to further improve globally cultivated, relatively high-yielding Green Revolution varieties (GRVs) derived from the SEMIDWARF 1 (SD1) gene3,4. Here we propose that precise regulation of the phytohormone gibberellin (GA) to optimal levels is the key to not only confer alkali-thermal tolerance to GRVs, but also to further enhance their yield. Endogenous modulation of ALKALI-THERMAL TOLERANCE 1/2 (ATT1/2), quantitative trait loci encoding GA20-oxidases or exogenous application of GA minimized rice yield loss affected by sodic soils. Mechanistically, high GA concentrations induce reactive oxygen species over-accumulation, whereas low GA concentrations repress the expression of stress-tolerance genes by means of DELLA-NGR5-mediated H3K27me3 methylation. We further showed that ATT1 induces large fluctuations in GA levels, whereas ATT2 is the ideal candidate for fine-tuning GA concentrations to appropriate levels to balance reactive oxygen species and H3K27me3 methylation to improve alkali-thermal tolerance and yield. Thus, ATT2 is expected to be a potential new post-Green Revolution gene that could be harnessed to develop and use marginal lands for sustainable agriculture in the future.
Abiotic, Agricultural genetics, Gibberellins, Plant genetics
Global meta-analysis shows action is needed to halt genetic diversity loss
Original Paper | Conservation biology | 2025-01-28 19:00 EST
Robyn E. Shaw, Katherine A. Farquharson, Michael W. Bruford, David J. Coates, Carole P. Elliott, Joachim Mergeay, Kym M. Ottewell, Gernot Segelbacher, Sean Hoban, Christina Hvilsom, Sílvia Pérez-Espona, Dainis Ruņģis, Filippos Aravanopoulos, Laura D. Bertola, Helena Cotrim, Karen Cox, Vlatka Cubric-Curik, Robert Ekblom, José A. Godoy, Maciej K. Konopiński, Linda Laikre, Isa-Rita M. Russo, Nevena Veličković, Philippine Vergeer, Carles Vilà, Vladimir Brajkovic, David L. Field, William P. Goodall-Copestake, Frank Hailer, Tara Hopley, Frank E. Zachos, Paulo C. Alves, Aleksandra Biedrzycka, Rachel M. Binks, Joukje Buiteveld, Elena Buzan, Margaret Byrne, Barton Huntley, Laura Iacolina, Naomi L. P. Keehnen, Peter Klinga, Alexander Kopatz, Sara Kurland, Jennifer A. Leonard, Chiara Manfrin, Alexis Marchesini, Melissa A. Millar, Pablo Orozco-terWengel, Jente Ottenburghs, Diana Posledovich, Peter B. Spencer, Nikolaos Tourvas, Tina Unuk Nahberger, Pim van Hooft, Rita Verbylaite, Cristiano Vernesi, Catherine E. Grueber
Mitigating loss of genetic diversity is a major global biodiversity challenge1,2,3,4. To meet recent international commitments to maintain genetic diversity within species5,6, we need to understand relationships between threats, conservation management and genetic diversity change. Here we conduct a global analysis of genetic diversity change via meta-analysis of all available temporal measures of genetic diversity from more than three decades of research. We show that within-population genetic diversity is being lost over timescales likely to have been impacted by human activities, and that some conservation actions may mitigate this loss. Our dataset includes 628 species (animals, plants, fungi and chromists) across all terrestrial and most marine realms on Earth. Threats impacted two-thirds of the populations that we analysed, and less than half of the populations analysed received conservation management. Genetic diversity loss occurs globally and is a realistic prediction for many species, especially birds and mammals, in the face of threats such as land use change, disease, abiotic natural phenomena and harvesting or harassment. Conservation strategies designed to improve environmental conditions, increase population growth rates and introduce new individuals (for example, restoring connectivity or performing translocations) may maintain or even increase genetic diversity. Our findings underscore the urgent need for active, genetically informed conservation interventions to halt genetic diversity loss.
Conservation biology, Genetic variation
Enhanced energy storage in antiferroelectrics via antipolar frustration
Original Paper | Electrical and electronic engineering | 2025-01-28 19:00 EST
Bingbing Yang, Yiqian Liu, Ru-Jian Jiang, Shun Lan, Su-Zhen Liu, Zhifang Zhou, Lvye Dou, Min Zhang, Houbing Huang, Long-Qing Chen, Yin-Lian Zhu, Shujun Zhang, Xiu-Liang Ma, Ce-Wen Nan, Yuan-Hua Lin
Dielectric-based energy storage capacitors characterized with fast charging and discharging speed and reliability1,2,3,4 play a vital role in cutting-edge electrical and electronic equipment. In pursuit of capacitor miniaturization and integration, dielectrics must offer high energy density and efficiency5. Antiferroelectrics with antiparallel dipole configurations have been of significant interest for high-performance energy storage due to their negligible remanent polarization and high maximum polarization in the field-induced ferroelectric state6,7,8. However, the low antiferroelectric-ferroelectric phase-transition field and accompanying large hysteresis loss deteriorate energy density and reliability. Here, guided by phase-field simulations, we propose a new strategy to frustrate antipolar ordering in antiferroelectrics by incorporating non-polar or polar components. Our experiments demonstrate that this approach effectively tunes the antiferroelectric-ferroelectric phase-transition fields and simultaneously reduces hysteresis loss. In PbZrO3-based films, we hence realized a record high energy density among all antiferroelectrics of 189 J cm-3 along with a high efficiency of 81% at an electric field of 5.51 MV cm-1, which rivals the most state-of-the-art energy storage dielectrics9,10,11,12. Atomic-scale characterization by scanning transmission electron microscopy directly revealed that the dispersed non-polar regions frustrate the long-range antipolar ordering, which contributes to the improved performance. This strategy presents new opportunities to manipulate polarization profiles and enhance energy storage performances in antiferroelectrics.
Electrical and electronic engineering, Electronic properties and materials, Ferroelectrics and multiferroics
Nature Materials
Dynamic flow control through active matter programming language
Original Paper | Biomedical engineering | 2025-01-28 19:00 EST
Fan Yang, Shichen Liu, Heun Jin Lee, Rob Phillips, Matt Thomson
Cells use ‘active' energy-consuming motor and filament protein networks to control micrometre-scale transport and fluid flows. Biological active materials could be used in dynamically programmable devices that achieve spatial and temporal resolution that exceeds current microfluidic technologies. However, reconstituted motor-microtubule systems generate chaotic flows and cannot be directly harnessed for engineering applications. Here we develop a light-controlled programming strategy for biological active matter to construct micrometre-scale fluid flow fields for transport, separation and mixing. We circumvent nonlinear dynamic effects within the active fluids by limiting hydrodynamic interactions between contracting motor-filament networks patterned with light. Using a predictive model, we design and apply flow fields to accomplish canonical microfluidic tasks such as transporting and separating cell clusters, probing the extensional rheology of polymers and giant lipid vesicles and generating mixing flows at low Reynolds numbers. Our findings provide a framework for programming dynamic flows and demonstrate the potential of active matter systems as an engineering technology.
Biomedical engineering, Biophysical methods
Non-fullerene acceptors with high crystallinity and photoluminescence quantum yield enable >20% efficiency organic solar cells
Original Paper | Materials for devices | 2025-01-28 19:00 EST
Chao Li, Jiali Song, Hanjian Lai, Huotian Zhang, Rongkun Zhou, Jinqiu Xu, Haodong Huang, Liming Liu, Jiaxin Gao, Yuxuan Li, Min Hun Jee, Zilong Zheng, Sha Liu, Jun Yan, Xian-Kai Chen, Zheng Tang, Chen Zhang, Han Young Woo, Feng He, Feng Gao, He Yan, Yanming Sun
The rational design of non-fullerene acceptors (NFAs) with both high crystallinity and photoluminescence quantum yield (PLQY) is of crucial importance for achieving high-efficiency and low-energy-loss organic solar cells (OSCs). However, increasing the crystallinity of an NFA tends to decrease its PLQY, which results in a high non-radiative energy loss in OSCs. Here we demonstrate that the crystallinity and PLQY of NFAs can be fine-tuned by asymmetrically adapting the branching position of alkyl chains on the thiophene unit of the L8-BO acceptor. It was found that L8-BO-C4, with 2-butyloctyl on one side and 4-butyldecyl on the other side, can simultaneously achieve high crystallinity and PLQY. A high efficiency of 20.42% (certified as 20.1%) with an open-circuit voltage of 0.894 V and a fill factor of 81.6% is achieved for the single-junction OSC. This work reveals how important the strategy of shifting the alkyl chain branching position is in developing high-performance NFAs for efficient OSCs.
Materials for devices, Solar cells
Nature Reviews Materials
Design of oxide nanoparticles for biomedical applications
Review Paper | Biomedical materials | 2025-01-28 19:00 EST
Bowon Lee, Yunjung Lee, Nohyun Lee, Dokyoon Kim, Taeghwan Hyeon
Oxide nanoparticles have garnered significant attention in biomedical research owing to the numerous available synthetic approaches and highly tunable physicochemical properties, which enable diverse functions within biological systems. These nanoparticles can be broadly categorized based on their characteristics useful for biomedical applications. Magnetic oxide nanoparticles, for instance, are prominently used as contrast agents in MRI and as mediators to generate heat, mechanical force or electricity for therapy. Catalytic oxide nanoparticles can generate or eliminate reactive oxygen species, which are central to numerous biological processes. Porous oxide nanoparticles are adept at loading dye or drug molecules, making them invaluable for bioimaging and therapeutic interventions. In this Review, we highlight strategies for the fabrication and advanced engineering of oxide nanoparticles tailored for biomedical applications. We primarily focus on iron oxide, ceria and silica nanoparticles, delving into their diagnostic and therapeutic potentials. We also discuss future prospects and the challenges that must be addressed to meet clinical needs.
Biomedical materials, Drug delivery, Medical imaging, Nanoparticles, Therapeutics
Physical Review Letters
Exploring New Physics with PandaX-4T Low Energy Electronic Recoil Data
Research article | Dark matter direct detection | 2025-01-29 05:00 EST
Xinning Zeng et al. (PandaX Collaboration)
New particles beyond the standard model of particle physics, such as axions, can be effectively searched through their interactions with electrons. We use the large liquid xenon detector PandaX-4T to search for novel electronic recoil signals induced by solar axions, neutrinos with anomalous magnetic moment, axionlike particles, dark photons, and light fermionic dark matter. A detailed background model is established using the latest datasets with \(1.54\text{ }\text{ }\mathrm{ton}\text{ }\mathrm{yr}\) exposure. No significant excess above the background has been observed, and we have obtained competitive constraints for axion couplings, neutrino magnetic moment, and fermionic dark matter interactions.
Phys. Rev. Lett. 134, 041001 (2025)
Dark matter direct detection, Particle dark matter, Solar neutrinos, Axion-like particles, Axions
Anderson Transition for Light in a Three-Dimensional Random Medium
Research article | Anderson localization | 2025-01-29 05:00 EST
Alexey Yamilov, Hui Cao, and Sergey E. Skipetrov
Simulations demonstrate that light can be confined within a scattering medium in a way similar to electrons in a disordered metal.
Phys. Rev. Lett. 134, 046302 (2025)
Anderson localization, Localization, Random & disordered media
Anisotropic Skyrmion and Multi-\(q\) Spin Dynamics in Centrosymmetric \({\mathrm{Gd}}_{2}{\mathrm{PdSi}}_{3}\)
Research article | Frustrated magnetism | 2025-01-29 05:00 EST
M. Gomilšek, T. J. Hicken, M. N. Wilson, K. J. A. Franke, B. M. Huddart, A. Štefančič, S. J. R. Holt, G. Balakrishnan, D. A. Mayoh, M. T. Birch, S. H. Moody, H. Luetkens, Z. Guguchia, M. T. F. Telling, P. J. Baker, S. J. Clark, and T. Lancaster
Skyrmions are particlelike vortices of magnetization with nontrivial topology, which are usually stabilized by Dzyaloshinskii-Moriya interactions (DMI) in noncentrosymmetric bulk materials. Exceptions are centrosymmetric Gd- and Eu-based skyrmion-lattice (SL) hosts with zero DMI, where both the SL stabilization mechanisms and magnetic ground states remain controversial. We address these here by investigating both the static and dynamical spin properties of the centrosymmetric SL host \({\mathrm{Gd}}_{2}{\mathrm{PdSi}}_{3}\) using muon spectroscopy. We find that spin fluctuations in the noncoplanar SL phase are highly anisotropic, implying that spin anisotropy plays a prominent role in stabilizing this phase. We also observe strongly anisotropic spin dynamics in the ground-state (IC-1) incommensurate magnetic phase of the material, indicating that it hosts a meronlike multi-\(q\) structure. In contrast, the higher-field, coplanar IC-2 phase is found to be single \(q\) with nearly isotropic spin dynamics.
Phys. Rev. Lett. 134, 046702 (2025)
Frustrated magnetism, Magnetic anisotropy, RKKY interaction, Skyrmions, Topological materials, AC susceptibility measurements, Density functional theory, Energy-dispersive x-ray spectroscopy, Muon spin relaxation & rotation, Scanning electron microscopy
Electrically Switchable Longitudinal Nonlinear Conductivity in Magnetic Semiconductors
Research article | Magnetoelectric effect | 2025-01-29 05:00 EST
Hong Jian Zhao, Yuhao Fu, Yurong Yang, Yanchao Wang, Laurent Bellaiche, and Yanming Ma
Writing data by electric field (as opposed to electric current) offers promises for energy efficient memory devices. While this data writing scheme is enabled by the magnetoelectric effect, the narrow spectrum of room-temperature magnetoelectrics hinders the design of practical magnetoelectric memories, and the exploration of other mechanisms toward low-power memories is greatly demanding. Here, we propose a mechanism that allows the electric-field writing of data beyond the framework of magnetoelectric effect. By symmetry analysis, we show that electric field can induce longitudinal nonlinear conductivity (LNC) in a wide spectrum of magnetic materials, including ferromagnets, antiferromagnets, magnetoelectrics, and nonmagnetoelectrics. The LNC is electrically switchable by reversing the electric field, where the switched LNC is detectable by transport measurements. Our first-principles simulations combined with transport calculations further predict \({\mathrm{YFeO}}_{3}\) and \({\mathrm{CuFeS}}_{2}\) (room-temperature antiferromagnets) to showcase electrically switchable LNC. Our Letter helps enrich the research avenues in nonlinear charge transport, and offers a pathway for designing energy efficient devices based on LNC.
Phys. Rev. Lett. 134, 046801 (2025)
Magnetoelectric effect, Antiferromagnets, Multiferroics, First-principles calculations, k dot p method
Macroscopic Stochastic Model for Economic Cycle Dynamics
Research article | Collective dynamics | 2025-01-29 05:00 EST
Sören Nagel, Jobst Heitzig, and Eckehard Schöll
We present a stochastic dynamic model which can explain economic cycles. We show that the macroscopic description yields a complex dynamical landscape consisting of multiple stable fixed points, each corresponding to a split of the population into a large low and a small high income group. The stochastic fluctuations induce switching between the resulting metastable states and excitation oscillations just below a deterministic bifurcation. The shocks are caused by the decisions of a few agents who have a disproportionate influence over the macroscopic state of the economy due to the unequal distribution of wealth among the population. The fluctuations have a long-term effect on the growth of economic output and lead to business cycle oscillations exhibiting coherence resonance, where the correlation time is controlled by the population size which is inversely proportional to the noise intensity.
Phys. Rev. Lett. 134, 047402 (2025)
Collective dynamics, Econophysics, Social dynamics, Stochastic dynamical systems, Langevin equation, Stochastic differential equations
Void Connectivity and Criticality in the Compression-Induced Gel-to-Glass Transition of Short-Range Attractive Colloids
Research article | Critical phenomena | 2025-01-29 05:00 EST
Michio Tateno, Yinqiao Wang, and Hajime Tanaka
Gels and attractive glasses---both dynamically arrested states formed through short-range attraction---are commonly found in a range of soft matter systems, including colloids, emulsions, proteins, and wet granular materials. Previous studies have revealed intriguing similarities and distinctions in their structural, dynamic, vibrational, and mechanical properties. However, the microstructural mechanisms underlying the gel-to-glass transition remain elusive. To address this, we investigate uniaxial compression-induced gel collapse using confocal microscopy, which provides experimental access to the relationship between mechanical stress and microstructure. Together with Brownian dynamics simulations, our study reveals two sequential transitions in void structure: from gels with percolating voids to isolated voids, and ultimately to voidless glasses. These transitions are closely linked to a shift from superlinear power-law scaling to explosive divergence toward the packing limit in both normal and deviatoric stresses as a function of volume fraction, particularly at lower temperatures. Understanding these mechanically self-organized transitions and their associated criticality deepens our insight into disordered solids, enabling better control over mechanical properties, interfacial characteristics, and transport behavior in porous materials.
Phys. Rev. Lett. 134, 048201 (2025)
Critical phenomena, Elastic deformation, Percolation, Phase transitions, Colloidal gel, Colloidal glass, Brownian dynamics, Confocal imaging
Physical Review X
Generalized Hydrodynamics: A Perspective
Perspective | Eigenstate thermalization | 2025-01-29 05:00 EST
Benjamin Doyon, Sarang Gopalakrishnan, Frederik Møller, Jörg Schmiedmayer, and Romain Vasseur
Conventional hydrodynamics describes systems with few long-lived excitations. In one dimension, however, many experimentally relevant systems feature a large number of long-lived excitations and conserved quantities even at high temperature, because they are proximate to integrable limits. Such mode…
Phys. Rev. X 15, 010501 (2025)
Eigenstate thermalization, Quantum many-body systems, Hydrodynamics, Many-body techniques
Interfacial Morphodynamics of Proliferating Microbial Communities
Research article | Bacterial communities | 2025-01-29 05:00 EST
Alejandro Martínez-Calvo, Carolina Trenado-Yuste, Hyunseok Lee, Jeff Gore, Ned S. Wingreen, and Sujit S. Datta
The shape of interfaces between domains of differing cell types arises from differences in cell proliferation rates and substrate friction, an insight that offers a biophysical basis for understanding such interfaces in microbial communities.
Phys. Rev. X 15, 011016 (2025)
Bacterial communities, Cellular organization, physiology & dynamics, Collective behavior, Complex systems, Continuum mechanics, Emergence of patterns, Fingering instability, Growth, Growth processes, Instability of free-surface flows, Interfacial flows, Living matter & active matter, Low Reynolds number flows, Nonlinear dynamics in fluids, Pattern formation, Patterns in complex systems, Phase diagrams, Roughness, Surface & interfacial phenomena, Surface instabilities, Bacteria, Biofilms, Biological materials, Collective dynamics, Interfaces, Coarse graining, Direct numerical simulations, Spatial modeling, Theories of collective dynamics & active matter
arXiv
Influence of Humidity on the Resistive Switching of Hexagonal Boron Nitride-Based Memristors
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Lukas Völkel, Rana Walied Ahmad, Alana Bestaeva, Dennis Braun, Sofía Cruces, Jimin Lee, Sergej Pasko, Simonas Krotkus, Michael Heuken, Stephan Menzel, Max C. Lemme
Two-dimensional material-based memristors have recently gained attention as components of future neuromorphic computing concepts. However, their surrounding atmosphere can influence their behavior. In this work, we investigate the resistive switching behavior of hexagonal boron nitride-based memristors with active nickel electrodes under vacuum conditions. Our cells exhibit repeatable, bipolar, nonvolatile switching under voltage stress after initial forming, with a switching window > 10\({^3}\) under ambient conditions. However, in a vacuum, the forming is suppressed, and hence, no switching is observed. Compact model simulations can reproduce the set kinetics of our cells under ambient conditions and predict highly suppressed resistive switching in a water-deficient environment, supporting the experimental results. Our findings have important implications for the application of h-BN-based memristors with electrochemically active electrodes since semiconductor chips are typically processed under high vacuum conditions and encapsulated to protect them from atmospheric influences.
Materials Science (cond-mat.mtrl-sci), Applied Physics (physics.app-ph)
18 pages, 4 Figures, 1 Table
Optical coherence and hyperfine structure of the 7F0-5D0 transition in EuCaWO4
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Xiantong An, Weiye Sun, Zhehao Xu, Wanting Xiao, Miaomiao Ren, Mucheng Guo, Shuping Liu, Fudong Wang, Manjin Zhong
Rare-earth ions doped in crystals with low nuclear-spin densities are highly promising candidates for quantum technology applications. In this study, we investigated the spectroscopic properties of the 7F0 - 5 D0 optical and the hyperfine transitions of Eu3+ ions in a CaWO4 crystal, where the nuclear spin arises solely from the 183W isotope, with a natural abundance of 14%. At a temperature of 3 K, we experimentally identified four distinct crystal field environments for Eu3+ ions in a 0.1 at.% Eu3+ doped CaWO4 crystal. The optical coherence properties of Eu3+ ions in these environments were characterized. Additionally, we resolved the hyperfine structures in the 7F0 ground state and 5D0 excited state, and determined the 7F0 ground state lifetimes using spectral hole-burning techniques. These findings highlight the significant potential of Eu3+:CaWO4 for optical quantum memory applications.
Materials Science (cond-mat.mtrl-sci)
Separate surface and bulk topological Anderson localization transitions in disordered axion insulators
New Submission | Disordered Systems and Neural Networks (cond-mat.dis-nn) | 2025-01-29 20:00 EST
Cormac Grindall, Alexander C. Tyner, Ang-Kun Wu, Taylor L. Hughes, J. H. Pixley
In topological phases of matter for which the bulk and boundary support distinct electronic gaps, there exists the possibility of decoupled mobility gaps in the presence of disorder. This is in analogy with the well-studied problem of realizing separate or concomitant bulk-boundary criticality in conventional Landau theory. Using a three-dimensional axion insulator having clean, gapped surfaces with \(e^2/2h\) quantized Hall conductance, we show the bulk and surface mobility gap evolve differently in the presence of disorder. The decoupling of the bulk and surface topology yields a regime that realizes a two-dimensional, unquantized anomalous Hall metal in the Gaussian unitary ensemble (GUE), which shares some spectral and response properties akin to the surface states of a conventional three-dimensional (3D) topological insulator. The generality of these results as well as extensions to other insulators and superconductors is discussed.
Disordered Systems and Neural Networks (cond-mat.dis-nn), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Strongly Correlated Electrons (cond-mat.str-el)
6 + 10 pages, 3 + 11 Figures
Two Channel Kondo behavior in the quantum XX chain with a boundary defect
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-29 20:00 EST
Yicheng Tang, Pradip Kattel, J.H. Pixley, Natan Andrei
We demonstrate that a boundary defect in the single spin-\(\frac{1}{2}\) quantum \(XX\) chain exhibits two-channel Kondo physics. Due to the presence of the defect, the edge spin fractionalizes into two Majorana fermions, out of which one decouples, and one is overscreened by the free fermion in bulk, leading to non-trivial boundary behavior characteristic of the two-channel Kondo model. When the ratio of boundary to bulk coupling exceeds a critical value of \(\sqrt{2}\), a massive boundary-bound mode is exponentially localized near the impurity site for strong impurity coupling. This leads to unusual behavior in physical quantities, such as the \(g\)-function not being monotonic. We compute the \(g-\)function of the impurity from both thermodynamic and entanglement entropy calculations and show that it takes a non-integer value of \(\sqrt{2}\) just as in the two-channel Kondo problem.
Strongly Correlated Electrons (cond-mat.str-el), Statistical Mechanics (cond-mat.stat-mech), High Energy Physics - Theory (hep-th), Mathematical Physics (math-ph), Quantum Physics (quant-ph)
5 pages, 4 Figures
The foot, the fan, and the cuprate phase diagram: Fermi-volume-changing quantum phase transitions
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-29 20:00 EST
A Fermi liquid with a
large' Fermi surface (FL) can have a quantum phase transition to a spin density wave state (SDW) with reconstructedsmall'
Fermi pockets. Both FL and SDW phases obey the Luttinger constraints on
the volume enclosed by the Fermi surfaces. The critical spin
fluctuations lead to spin-singlet \(d\)-wave pairing, as observed in the
cuprates. Studies of the influence of spatial disorder on the SDW-FL
quantum phase transition predict an extended quantum-critical
Griffiths-type phase at low temperatures on the large Fermi surface
side. These computations agree with the
foot' seen in transport, and recent low temperature neutron scattering observations on La$_{2-x}$Sr$_x$CuO$_4$. However, this theory cannot explain the higher temperature pseudogap and thefan'
of strange metal of the hole-doped cuprates. Here we need to consider
underlying Fermi-volume-changing quantum phase transitions without
symmetry breaking. Then the small Fermi surface phase does not obey the
Luttinger constraint, and is instead a `fractionalized Fermi liquid'
(FL). A theory of FLin single band models describes photoemission
observations in the pseudogap phase. The FL-FL quantum phase transition,
and the influence of spatial disorder, is described by an analysis
inspired by the Sachdev-Ye-Kitaev model. This theory successfully
describes linear-in-temperature resistivity, optical conductivity and
thermopower observations. The crossovers connecting these lower and
higher temperature descriptions are also discussed.
Strongly Correlated Electrons (cond-mat.str-el), High Energy Physics - Theory (hep-th), Quantum Physics (quant-ph)
31 pages, 11 figures; Contribution to the memorial volume for Jan Zaanen
Quantum geometric bounds in spinful systems with trivial band topology
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-29 20:00 EST
Wojciech J. Jankowski, Robert-Jan Slager, Gunnar F. Lange
We derive quantum geometric bounds in spinful systems with spin-topology characterized by a single \(\mathbb{Z}\)-index protected by a spin gap. Our bounds provide geometric conditions on the spin topology, distinct from the known quantum geometric bounds associated with Wilson loops and nontrivial band topologies. As a result, we obtain stricter bounds in time-reversal symmetric systems with a nontrivial \(\mathbb{Z}_2\) index and also bounds in systems with a trivial \(\mathbb{Z}_2\) index, where quantum metric should be otherwise unbounded. We benchmark these findings with first-principles calculations in elemental Bismuth realizing higher even nontrivial spin-Chern numbers. Moreover, we connect these bounds to optical responses, demonstrating that spin-resolved quantum geometry can be observed experimentally. Finally, we connect spin-bounds to quantum Fisher information and Cramér-Rao bounds which are central to quantum metrology, showing that the elemental Bi and other spin-topological phases hold promises for topological free fermion quantum sensors.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci), Optics (physics.optics), Quantum Physics (quant-ph)
5+11 pages, 3+3 figures
Critical gate distance for Wigner crystallization in the two-dimensional electron gas
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-29 20:00 EST
Agnes Valenti, Vladimir Calvera, Yubo Yang, Miguel A. Morales, Steven A. Kivelson, Ilya Esterlis, Shiwei Zhang
We report on the properties of the two-dimensional electron gas in a dual-gate geometry, using quantum Monte Carlo methods to obtain aspects of the phase diagram as a function of electron density and gate distance. We identify the critical gate distance below which the Wigner crystal phase disappears. For larger gate distances, the system undergoes a re-entrant transition from crystal to liquid at sufficiently low density. We also present preliminary evidence for a fully polarized ferromagnetic liquid state at low electron density and intermediate gate distances. The quantum Monte Carlo results are compared with simpler approximate methods, which are shown to be semi-quantitatively reliable for determining key features of the phase diagram. These methods are then used to obtain the phase boundary between the Wigner crystal and liquid in the single-gate geometry.
Strongly Correlated Electrons (cond-mat.str-el), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Statistical Mechanics (cond-mat.stat-mech)
4+4 pages
Crosstalk analysis in single hole-spin qubits within highly anisotropic g-tensors
New Submission | Other Condensed Matter (cond-mat.other) | 2025-01-29 20:00 EST
Yaser Hajati, Irina Heinz, Guido Burkard
Spin qubits based on valence band hole states are highly promising for quantum information processing due to their strong spin-orbit coupling and ultrafast operation speed. As these systems scale up, achieving high-fidelity single-qubit operations becomes essential. However, mitigating crosstalk effects from neighboring qubits in larger arrays, particularly for anisotropic qubits with strong spin-orbit coupling, presents a significant challenge. We investigate the impact of crosstalk on qubit fidelities during single-qubit operations and derive an analytical equation that serves as a synchronization condition to eliminate crosstalk in anisotropic media. Our analysis proposes optimized driving field conditions that can robustly synchronize Rabi oscillations and minimize crosstalk, showing a strong dependence on qubit anisotropy and the orientation of the external magnetic field. Taking experimental data into our analysis, we identify a set of parameter values that enable nearly crosstalk-free single-qubit gates, thereby paving the way for scalable quantum computing architectures.
Other Condensed Matter (cond-mat.other), Quantum Physics (quant-ph)
Microrheological model for Kelvin-Voigt materials with micro-heterogeneities
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-29 20:00 EST
T. N. Azevedo, K. M. Oliveira, H. P. Maia, A. V. N. C. Teixeira, L. G. Rizzi
We introduce a generalization of the Kelvin-Voigt model in order to include and characterize heterogeneities in viscoelastic semisolid materials. By considering a microrheological approach, we present analytical expressions for the mean square displacement and for the time-dependent diffusion coefficient of probe particles immersed in a viscoelastic material described by this model. Besides validating our theoretical approach through Brownian dynamics simulations, we show how the model can be used to describe experimental data obtained for polyacrylamide and laponite gels.
Soft Condensed Matter (cond-mat.soft), Materials Science (cond-mat.mtrl-sci), Statistical Mechanics (cond-mat.stat-mech), Computational Physics (physics.comp-ph)
10 pages, 6 figures, 44 references. This manuscript corresponds to the submitted version of the article published as part of the themed collection: Soft Matter Emerging Investigators Series in Soft Matter Journal
Soft Matter (2025)
Electrically tunable Floquet Weyl photon emission from Dirac semimetal Cd3As2
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Sobhan Subhra Mishra, Thomas CaiWei Tan, Manoj Gupta, Faxian Xiu, Ranjan Singh
The ability to optically engineer the Dirac band and electrically control the Fermi level in two-dimensional (2D) Dirac systems, such as graphene, has significantly advanced quantum technologies. However, similar tunability has remained elusive in three-dimensional Dirac systems. In this work, we demonstrate both optical and electrical tunability of the band structure in the 3D Dirac semimetal Cd3As2. Photoexcitation with circularly polarized light breaks time-reversal symmetry, lifting the degeneracy at Dirac points to transform the material into a Floquet Weyl semimetal with chiral Weyl nodes. This transition induces nonzero Berry curvature, giving rise to helicity-dependent transverse anomalous photocurrents, detectable through terahertz emission at normal incidence. Furthermore, applying an external electric field displaces the Fermi level away from the Dirac point, enlarging the Dirac cone projection leading to a reduced density of states of Fermi arcs. As a result, we achieve precise electrical control over Floquet band engineering, resulting in a large modulation of THz emission. Moreover, at oblique incidence, the circular photon-drag effect induces helicity-dependent longitudinal photocurrents. Simultaneous generation and manipulation of both longitudinal and transverse photocurrents enable precise control of the helicity of emitted THz pulses. These results pave the way for electric field-controlled Floquet Weyl THz sources, offering significant potential for applications in quantum computing and low-power electronics.
Materials Science (cond-mat.mtrl-sci)
26 pages, 4 figures, 4 supplementary figures
Nanostructured superlattices as a probe of fermiology in Weyl-semimetal NbP
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-29 20:00 EST
Nathan C. Drucker, Federico Balduini, Jules Schadt, Lorenzo Rocchino, Tathagata Paul, Vicky Hasse, Claudia Felser, Cezar B. Zota, Bernd Gotsmann
When a charged particle is subject to both a periodic potential and magnetic field, oscillations in its conductivity occur when the field-induced cyclotron radius is commensurate with the period of the potential. This effect has been observed in two-dimensional systems including electron gases and graphene, and is related to the Hofstadter spectrum of magnetic minibands. Here we show that commensuration oscillations also can arise in the ballistic transport regime of a nanostructured 3D material, with the Weyl semimetal NbP. These oscillations encode information about the quasiparticles at the Fermi-surface, including their momentum, charge, mass, and rotational symmetry. In particular, we use the magnetic field and temperature dependence of the commensuration oscillations to extract the Fermi-momenta and quasiparticle mass, in good agreement with Shubnikov-de Haas quantum oscillations. Furthermore, we investigate the relationship between the engineered superlattice symmetry and resistivity response based on the symmetry of the Fermi surface and charge of the quasiparticles. These results demonstrate how nanopatterned superlattices can be used to characterize a 3D materials' fermiology, and also point towards new ways of engineering quantum transport in these systems.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
25 Pages, 4 main figures, 4 supplementary figures
Reentrant localization transition in a dimerized quasiperiodic dipolar chain
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-29 20:00 EST
Thomas F. Allard, Guillaume Weick
Reentrant localization transitions, that is, the transitions of a portion of the eigenspectrum from localized to critical and then again to localized as the disorder strength is increased, have been recently unveiled in various quasiperiodic models. However, how these transitions may extend to systems with long-range coupling and dissipation remains elusive. Here we investigate the fate of such a phenomenon in a dimerized quasiperiodic chain of dipolar emitters with all-to-all coupling. Through an extensive study of the spectral properties of our model, we demonstrate that such anomalous transitions survive to all-to-all couplings when considering a staggered quasiperiodic modulation of the spacings between the emitters. Transport simulations through a driven-dissipative open quantum system approach complete our study and reveal the effects of emitter losses on the reentrant localization transition.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Disordered Systems and Neural Networks (cond-mat.dis-nn)
10 pages, 8 figures
Analytical dispersion relation for forward volume spin waves in ferrimagnets near the angular momentum compensation condition
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Luis Sánchez-Tejerina, David Osuna Ruiz, Víctor Raposo, Eduardo Martínez, Luis López Díaz, Óscar Alejos
Antiferromagnetic magnonics has become the focus of intense scientific research because of the advantages of these materials compared to ferromagnets. However, ferrimagnetic materials have received much less attention despite exhibiting similar dynamical features at the angular momentum compensation point. In this paper, we present analytical expressions describing the dispersion relation of forward volume spin waves in ferrimagnetic materials near the angular momentum compensation point. Besides, we benchmark the derived dispersion relations with full micromagnetic simulations showing a complete agreement between both approaches. This work predicts two different branches for forward volume spin waves in ferrimagnetic materials merging into a single branch at the angular momentum compensation point. Our results can assist in the design of magnonic devices built on ferrimagnetic materials.
Materials Science (cond-mat.mtrl-sci)
Anti-thixotropic dynamics in attractive colloidal dispersions: a shear restructuring driven by elastic stresses
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-29 20:00 EST
Julien Bauland, Gauthier Legrand, Sébastien Manneville, Thibaut Divoux, Arnaud Poulesquen, Thomas Gibaud
Due to rich rheological properties, dispersions of attractive colloidal particles are ubiquitous in industries. Specifically, upon experiencing a sudden reduction in shear rate, these dispersions may exhibit transient behaviors such as thixotropy-where viscosity increases over time-and anti-thixotropy, characterized by an initial viscosity decrease before reaching a steady state. While thixotropy has been described as a competition between structure buildup and disruption, the mechanisms of anti-thixotropy remain poorly understood. Here, we investigate the anti-thixotropic dynamics of carbon black particles dispersed in oil-a system known for exhibiting anti-thixotropy-through flow step-down experiments. Using a multi-technique approach combining rheology with velocimetry and structural characterizations, we show that viscosity decrease results from a decrease in wall slip concomitant to shear-induced structural rearrangements, indicating a transition from a dynamical network of fractal clusters into a network of loosely connected dense agglomerates. Additionally, after a characteristic anti-thixotropic time \(\tau\), a steady flow is reached. This time \(\tau\) diverges with increasing shear rate at a critical value corresponding to a Mason number of one, indicating that anti-thixotropy occurs only when colloidal attraction outweighs viscous forces. More precisely, we show that the structural rearrangement underpinning the viscosity decrease is mediated by elastic stresses \(\sigma_e\), such that \(\tau \propto \sigma_e^{-3}\). Finally, on long time scales, the steady state is linked to a microstructure with nearly zero yield stress, indicating a loss of flow memory. These findings provide a mechanism for anti-thixotropy and suggest pathways for controlling viscosity and yield stress in attractive colloidal dispersions.
Soft Condensed Matter (cond-mat.soft)
How to properly measure the fracture properties of brittle materials using molecular simulations? Application to mode I and mode III in silica glass
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Felix Weber, Maxime Vassaux, Lukas Laubert, Sebastian Pfaller
The fundamental understanding of the root causes of failure requires information on atomic-scale processes. Molecular dynamics (MD) simulations are widely used to provide these insights while maintaining chemical specificity. However, the boundary conditions that can be applied in MD fracture simulations are limited to the linear-elastic fracture mechanics (LEFM) far-field solution, posing restrictions in simulating bending or shearing deformations commonly applied in classical experimental setups. This has to date prevented the accurate and precise prediction of key fracture quantities such as critical stress intensity factors. To overcome these limitations, we here apply the domain-decomposition Capriccio method to couple atomistic MD samples representing silica glass synthesized at various quenching rates with the finite element (FE) method and perform both mode I (tension, three- and four-point bending) and mode III simulations at different loading rates. We investigate multiple criteria to best identify the onset of crack propagation based on the virial stress, the number of pair interactions, the kinetic energy/temperature, the crack velocity, and the crack opening displacement. Based on this, we propose a novel protocol that allows us to determine the fracture toughness of silica glass under mode I and III conditions from atomistic data with increased fidelity, with our results being in good agreement with experimental data and predictions from LEFM. Overall, our contribution demonstrates how coupled FE-MD simulations enable chemically specific quantitative predictions of the fracture behavior of amorphous materials under arbitrary mechanical loading conditions.
Materials Science (cond-mat.mtrl-sci)
Exploring the defect landscape and dopability of chalcogenide perovskite BaZrS3
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Rushik Desai (1), Shubhanshu Agarwal (2), Kiruba Catherine Vincent (2), Alejandro Strachan (1), Rakesh Agrawal (2), Arun Mannodi-Kanakkithodi (1) ((1) School of Materials Engineering, Purdue University, West Lafayette, IN, USA (2) School of Chemical Engineering, Purdue University, West Lafayette, IN, USA)
BaZrS3 is a chalcogenide perovskite that has shown great promise as a photovoltaic absorber over the last few years. Despite its impressive electronic and optical properties, native point defects and impurities could impose significant limitations on the photovoltaic performance of BaZrS3. Such defects may form spontaneously, create deep levels that act as traps for carriers, and influence the device performance by changing the concentrations of electrons and holes. On the other hand, functional dopants that dominate over native defects can help tune the nature of conductivity in BaZrS3. In this work, we applied first principles computations to comprehensively investigate the defect landscape of BaZrS3, including all intrinsic defects and select impurities and dopants. BaZrS3 intrinsically exhibits n-type equilibrium conductivity under Zr-rich and Zr-poor conditions, as determined by low energy vacancy and interstitial defects. O and H impurities create relatively low energy neutral and donor-type defects. La and Nb are calculated to be stable donor-type defects, which will make BaZrS3 even more n-type, whereas As and O form amphoteric defects, which generally show higher formation energies than native defects. This work highlights the difficulty of tuning the electrical properties of BaZrS3 via doping, especially making it more p-type. However, it points to some possible avenues to inform our future work.
Materials Science (cond-mat.mtrl-sci)
Landau-level composition of bound exciton states in magnetic field
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
We present a theory that studies the state composition of a bound exciton in magnetic field. Using a basis set made of products of free electron and hole wavefunctions in Landau gauge, we derive a secular equation which shows the relation between Landau levels (LLs) of the electron and hole when a bound exciton is formed. Focusing on excitons in the light cone, we establish a scattering selection rule for the interaction of an electron in LL \(n_\text{e}\) with a hole in LL \(n_\text{h}\). We solve the resulting secular equation and identify a simple pairing law, \(n_\text{e} = n_\text{h} + l\), which informs us on the construction of a bound exciton state with magnetic quantum number \(l\), and on the interaction of the exciton magnetic moment with magnetic field. We obtain good agreement between theory results and recent measurements of the diamagnetic shifts of exciton states in WSe\(_2\) monolayers.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
18 pages, 6 figures. We welcome your feedback
Adhesion and Reconstruction of Graphene/Hexagonal Boron Nitride Heterostructures: A Quantum Monte Carlo Study
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-29 20:00 EST
Marcin Szyniszewski, Elaheh Mostaani, Angelika Knothe, Vladimir Enaldiev, Andrea C. Ferrari, Vladimir I. Fal'ko, Neil D. Drummond
We investigate interlayer adhesion and relaxation at interfaces between graphene and hexagonal boron nitride (hBN) monolayers in van der Waals heterostructures. The adhesion potential between graphene and hBN is calculated as a function of local lattice offset using diffusion quantum Monte Carlo methods, which provide an accurate treatment of van der Waals interactions. Combining the adhesion potential with elasticity theory, we determine the relaxed structures of graphene and hBN layers at interfaces, finding no metastable structures. The adhesion potential is well described by simple Lennard-Jones pair potentials that we parameterize using our quantum Monte Carlo data. Encapsulation of graphene between near-aligned crystals of hBN gives rise to a moiré pattern whose period is determined by the misalignment angle between the hBN crystals superimposed over the moiré superlattice previously studied in graphene on an hBN substrate. We model minibands in such supermoiré superlattices and find them to be sensitive to a 180\(^\circ\) rotation of one of the encapsulating hBN crystals. We find that monolayer and bilayer graphene placed on a bulk hBN substrate and bulk hBN/graphene/bulk hBN systems do not relax to adopt a common lattice constant. The energetic balance is much closer for free-standing monolayer graphene/hBN bilayers and hBN/graphene/hBN trilayers. The layers in an alternating stack of graphene and hBN are predicted to strain to adopt a common lattice constant and hence we obtain a new, stable three-dimensional crystal with a unique electronic structure.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci)
Microscopic Theory of Polaron-Polariton Dispersion and Propagation
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-29 20:00 EST
Logan Blackham, Arshath Manjalingal, Saeed R. Koshkaki, Arkajit Mandal
We develop an analytical microscopic theory to describe the polaron-polariton dispersion, formed by hybridizing excitons, photons, and phonons, and their coherent dynamics inside optical cavities. Starting from a microscopic light-matter Hamiltonian, we derive a simple analytical model by pursuing a non-perturbative treatment of the phonon and photon couplings to excitons. Within our theoretical framework, the phonons are treated as classical fields that are then quantized via the Floquet formalism. We show that, to a good approximation, the entire polaron-polariton system can be described using a band picture despite the phonons breaking translational symmetry. Our theory also sheds light on the long-lived coherent ballistic motion of exciton-polaritons with high excitonic character that propagate with group velocities lower than is expected from pure exciton-polariton bands, offering a microscopic explanation for these puzzling experimental observations.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci), Chemical Physics (physics.chem-ph)
Pair Wavefunction Symmetry in UTe2 from Zero-Energy Surface State Visualization
New Submission | Superconductivity (cond-mat.supr-con) | 2025-01-29 20:00 EST
Qiangqiang Gu, Shuqiu Wang, Joseph P. Carroll, Kuanysh Zhussupbekov, Christopher Broyles, Sheng Ran, Nicholas P. Butch, Shanta Saha, Johnpierre Paglione, Xiaolong Liu, J.C. Séamus Davis, Dung-Hai Lee
Although nodal spin-triplet topological superconductivity appears probable in UTe2, its superconductive order-parameter {}_k remains unestablished. In theory, a distinctive identifier would be the existence of a superconductive topological surface band (TSB), which could facilitate zero-energy Andreev tunneling to an s-wave superconductor, and also distinguish a chiral from non-chiral {}_k via enhanced s-wave proximity. Here we employ s-wave superconductive scan-tips and detect intense zero-energy Andreev conductance at the UTe2 (0-11) termination surface. Imaging reveals sub-gap quasiparticle scattering interference signatures with a-axis orientation. The observed zero-energy Andreev peak splitting with enhanced s-wave proximity, signifies that {}_k of UTe2 is a non-chiral state: B1u, B2u or B3u. However, if the quasiparticle scattering along the a-axis is internodal, then a non-chiral B3u state is the most consistent for UTe2.
Superconductivity (cond-mat.supr-con), Materials Science (cond-mat.mtrl-sci)
45 pages, 5 figures, to appear in Science (2025)
Induced Interactions and Bipolarons in Spin-Orbit Coupled Bose-Einstein Condensates
New Submission | Quantum Gases (cond-mat.quant-gas) | 2025-01-29 20:00 EST
Zhe Yang, Shanshan Ding, Qizhong Zhu
Impurities immersed in a Bose-Einstein condensate (BEC) can interact indirectly through the exchange of Bogoliubov excitations. These impurities, which form dressed quasiparticles known as Bose polarons due to their interaction with the BEC, can pair up to form a bound state called bipolarons, via an induced interaction. Previous studies on induced interactions have primarily focused on cases with an isotropic excitation spectrum. In this work, we investigate the properties of induced interactions and bipolarons mediated by anisotropic Bogoliubov excitations using field theory. Taking a BEC with spin-orbit coupling as an example, we show that the induced interaction becomes anisotropic. Notably, a double-minima feature appears in the induced interaction in momentum space due to the exchange of roton excitations. Additionally, we calculate the binding energy and wave functions of these bipolarons induced by anisotropic interactions. Unlike previously studied bipolarons formed through the exchange of isotropic phonon excitations, we identify a new type of bipolarons whose wave functions feature a double-peak structure under strong impurity-boson interactions. Our work extends the theory of induced interactions from isotropic to anisotropic systems, and reveals the novel features in both the induced interactions and bipolarons arising from BEC with an unconventional excitation spectrum.
Quantum Gases (cond-mat.quant-gas)
7 pages, 6 figures. Comments are welcome
Correlation between ferroelectricity and torsional motion of acetyl groups in tris(4-acetylphenyl)amine observed by muon spin relaxation
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
J. G. Nakamura, M. Hiraishi, H. Okabe, A. Koda, R. Kumai, F. L. Pratt, R. Kadono
It is demonstrated by muon spin relaxation and resonance experiments that the switchable spontaneous polarization of the organic ferroelectric compound tris(4-acetylphenyl)amine (TAPA) is governed by the local molecular dynamics of the acetyl group. The implanted muon forms paramagnetic states which exhibit longitudinal spin relaxation due to the fluctuation of hyperfine fields exerted from unpaired electrons. The first-principle density functional theory calculations indicate that these states are muonated radicals localized at the phenyl group and on the carbon/oxygen of the acetyl group, thereby suggesting that the spin relaxation is dominated by the random torsional motion of acetyl group around the CC bond to the phenyl group. The stepwise change in the relative yield of radicals at \(T_0\approx 350\) K and the gradual increase in the spin relaxation rate with temperature (\(T\)) indicate that the torsional motion is significantly enhanced by thermal excitation above \(T_0\). This occurs concomitantly with the strong enhancement in the atomic displacement parameter of oxygen in the acetyl group (which is non-linear in \(T\)), indicating that it is the local molecular motion of the acetyl groups that drives the structural transition.
Materials Science (cond-mat.mtrl-sci)
5 figures, 9 pages
J. Appl. Phys. 137, 044102 (2025)
Small hole polarons in yellow phase \(\delta\)-CsPbI\(_3\)
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
A heterophase containing both the optically active \(\alpha\)-CsPbI\(_3\) and non-active \(\delta\)-CsPbI\(_3\) has been demonstrated as an efficient white light emitter. This has challenged the conventional perspective that non-active phases of perovskites are undesirable in any perovskite-based optoelectronic devices. To understand the role that the yellow phase \(\delta\)-CsPbI\(_3\) plays in the light emission process, we performed a systematic computational study on its electronic and optical properties, which are relatively unexplored in the literature. Using the Fröhlich model we showed that the electron and hole both exhibit moderate coupling to longitudinal optical phonons. Explicit density functional theory calculations show that small hole polarons exist with a formation energy of -96 meV, corresponding to the contraction of the Pb-I bonds within a [PbI\(_6\)] octahedra and wavefunction localization. Molecular dynamics simulations showed that the small hole polaron is stable against thermal disorder, and exhibit periodic localization and delocalization behavior similar to carrier hopping with a characteristic lifetime of 0.3 ps. Our results might have elucidated the role that \(\delta\)-CsPbI\(_3\) play in the self-trapped emission in perovskite-based white light emitting diodes by supporting the presence of a localized small hole polaron.
Materials Science (cond-mat.mtrl-sci)
21 pages, 3 figures
Unconventional Superconducting Phase Diagram of Monolayer WTe2
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-29 20:00 EST
Tiancheng Song, Yanyu Jia, Guo Yu, Yue Tang, Ayelet J. Uzan, Zhaoyi Joy Zheng, Haosen Guan, Michael Onyszczak, Ratnadwip Singha, Xin Gui, Kenji Watanabe, Takashi Taniguchi, Robert J. Cava, Leslie M. Schoop, N. P. Ong, Sanfeng Wu
The existence of a quantum critical point (QCP) and fluctuations around it are believed to be important for understanding the phase diagram in unconventional superconductors such as cuprates, iron pnictides, and heavy fermion superconductors. However, the QCP is usually buried deep within the superconducting dome and is difficult to investigate. The connection between quantum critical fluctuations and superconductivity remains an outstanding problem in condensed matter. Here combining both electrical transport and Nernst experiments, we explicitly demonstrate the onset of superconductivity at an unconventional QCP in gate-tuned monolayer tungsten ditelluride (WTe2), with features incompatible with the conventional Bardeen-Cooper-Schrieffer (BCS) scenario. The results lead to a novel superconducting phase diagram that is distinguished from other known superconductors. Two distinct gate-tuned quantum phase transitions are observed at the ends of the superconducting dome. We find that quantum fluctuations around the QCP of the underdoped regime are essential for understanding how the monolayer superconductivity is established. The unconventional phase diagram we report here illustrates a previously unknown relation between superconductivity and QCP.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Strongly Correlated Electrons (cond-mat.str-el), Superconductivity (cond-mat.supr-con)
Spin frustration and unconventional spin twisting state in van der Waals ferromagnet/antiferromagnet heterostructures
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Tianye Wang, Qian Li, Mengmeng Yang, Yu Sun, Alpha T. N'Diaye, Christoph Klewe, Andreas Scholl, Xianzhe Chen, Xiaoxi Huang, Hongrui Zhang, Santai Yang, Xixiang Zhang, Chanyong Hwang, Padraic C. Shafer, Michael F. Crommie, Ramamoorthy Ramesh, Zi Q. Qiu
Atomically flat surfaces of van der Waals (vdW) materials pave an avenue for addressing a long-standing fundamental issue of how a perfectly compensated antiferromagnet (AFM) surface frustrates a ferromagnetic (FM) overlayer in FM/AFM heterostructures. By revealing the AFM and FM spin structures separately in vdW Fe5GeTe2/NiPS3 heterostructures, we find that C-type in-plane AFM NiPS3 develops three equivalent AFM domains which are robust against external magnetic field and magnetic coupling with Fe5GeTe2. Consequently, spin frustration at the Fe5GeTe2/NiPS3 interface was shown to develop a perpendicular Fe5GeTe2 magnetization in the interfacial region that switches separately from the bulk of the Fe5GeTe2 magnetizations. In particular, we discover an unconventional spin twisting state that the Fe5GeTe2 spins twist from perpendicular direction near the interface to in-plane direction away from the interface in Fe5GeTe2/NiPS3. Our finding of the twisting spin texture is a unique property of spin frustration in van der Waals magnetic heterostructures.
Materials Science (cond-mat.mtrl-sci)
28 pages, 8 figures
Strongly Repulsive 1D Gases at Higher Branches: Spin-Charge Correlation and Coupled Spin-Chain Model
New Submission | Quantum Gases (cond-mat.quant-gas) | 2025-01-29 20:00 EST
We investigate the higher repulsive branches of one-dimensional (1D) bosonic and fermionic quantum gases beyond the super-Tonks-Girardeau regime, utilizing the Bethe-Ansatz method and exact diagonalization of small trapped clusters. In contrast to the well-studied lowest branches that are characterized by spin-charge separation, we demonstrate the emergence of strong spin-charge correlation in all higher branches with hard-core interactions. This manifests in distinct quasi-momentum distributions and energy spectra for bosons and spin-1/2 fermions, despite their fermionization. Furthermore, trapped fermions in higher branches exhibit novel spin textures, intricately linked to charge excitations, necessitating a coupled multi-chain description beyond single effective spin-chain models. Our findings unveil a rich interplay between spin and charge degrees of freedom in highly excited 1D systems, opening avenues for exploring novel quantum phenomena beyond the conventional paradigm of low-lying states.
Quantum Gases (cond-mat.quant-gas)
10 pages, 4 figures
Systematic investigation of dynamic nuclear polarization with boron vacancy in hexagonal boron nitride
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-29 20:00 EST
Yuki Nakamura, Shunsuke Nishimura, Takuya Iwasaki, Shu Nakaharai, Shinichi Ogawa, Yukinori Morita, Kenji Watanabe, Takashi Taniguchi, Kento Sasaki, Kensuke Kobayashi
Dynamic nuclear polarization (DNP) using the boron vacancy (\(\mathrm{V_B^-}\)) in hexagonal boron nitride (hBN) has gained increasing attention. Understanding this DNP requires systematically investigating the optically detected magnetic resonance (ODMR) spectra and developing a model that quantitatively describes its behavior. Here, we measure the ODMR spectra of \(\mathrm{V_B^-}\) in \(\mathrm{h}^{10}\mathrm{B}^{15}\mathrm{N}\) over a wide magnetic field range, including the ground state level anti-crossing (GSLAC), and compare them with the results of the Lindblad-based simulation that considers a single electron spin and three neighboring \(^{15}\mathrm{N}\) nuclear spins. Our simulation successfully reproduces the experimental spectra, including the vicinity of GSLAC. It can explain the overall behavior of the magnetic field dependence of the nuclear spin polarization estimated using the Lorentzian fitting of the spectra. Despite such qualitative agreement, we also demonstrate that the fitting methods cannot give accurate polarizations. Finally, we discuss that symmetry-induced mechanisms of \(\mathrm{V_B^-}\) limit the maximum polarization. Our study is an essential step toward a quantitative understanding of DNP using defects in hBN and its quantum applications.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Decomposition of entropy production for free-energy generation in a non-equilibrium dot with multiple electron states
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-01-29 20:00 EST
Chloe Salhani, Kensaku Chida, Takase Shimizu, Toshiaki Hayashi, Katsuhiko Nishiguchi
We experimentally demonstrate the decomposition of entropy production during free-energy generation in a nanometer-scale dot transitioning to a non-equilibrium steady state via single-electron counting statistics. An alternating-current signal driving a reservoir that injects multiple electrons into the dot makes it non-equilibrium, leading to free-energy generation, heat dissipation, and Shannon-entropy production. By analyzing the time-domain probability distributions of multiple electron states of the dot, we quantitatively decompose the heat dissipation into housekeeping and excess heats, revealing the correlation between the free energy and the decomposed components of heat dissipation. This correlation suggests that the ratio of the generated free energy to the work applied to the dot, can potentially reach 0.5 under far-from-equilibrium conditions induced by a large signal, while an efficiency of 0.25 was experimentally achieved. Our results, providing the theoretical and experimental efficiencies from the relation between decomposed heat dissipation and free-energy generation, promise to connect non-equilibrium thermodynamics perspectives to electronic devices.
Statistical Mechanics (cond-mat.stat-mech)
Laser patterning of the room temperature van der Waals ferromagnet 1\(T\)-CrTe\(_2\)
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Tristan Riccardi, Suman Sarkar, Anike Purbawati, Aloïs Arrighi, Marek Kostka, Abdellali Hadj-Azzem, Jan Vogel, Julien Renard, Laëtitia Marty, Amit Pawbake, Clément Faugeras, Kenji Watanabe, Takashi Taniguchi, Aurore Finco, Vincent Jacques, Lei Ren, Xavier Marie, Cedric Robert, Manuel Nuñez-Regueiro, Nicolas Rougemaille, Nedjma Bendiab, Johann Coraux
Lamellar crystalline materials, whose layers are bond by van der Waals forces, can be stacked to form ultrathin artificial heterostructures, and in particular vertical magnetic junctions when some of the stacked materials are (ferro)magnetic. Here, using the room temperature van der Waals ferromagnet 1\(T\)-CrTe\(_2\), we report a method for patterning lateral magnetic junctions. Exploiting the heat-induced phase transformation of the material into Cr\(_x\)Te\(_y\) compounds (\(x/y>1/2\)), we use local laser heating to imprint patterns at the micron-scale. Optimizing laser heat dissipation, we further demonstrate the crucial role of the substrate to control the phase transformation. If plain, unstructured poorly heat-conducting substrates allow for direct writing of magnetic patterns, structured \(h\)-BN layers can serve as heat stencils to draw potentially thinner patterns. Besides, \(h\)-BN encapsulation turns out to be heat-protective (in addition from protecting against oxidation as it is generally used for), allowing the demonstration of room temperature ferromagnetism in $<\(7~nm-thick 1\)T\(-CrTe\)_2$.
Materials Science (cond-mat.mtrl-sci)
accepted in Physical Review Materials, 5 figures
Quantum Geometric Origin of Strain-Tunable Giant Second-Harmonic Generation in Bi\(_2\)O\(_2\)X (X=S, Se, Te)
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Zhefeng Lou, Zhihao Gong, Ziye Zhu, Wenbin Li, Xiao Lin, Hua Wang
Two-dimensional (2D) materials with giant nonlinear optical (NLO) responses are essential for the development of advanced on-chip NLO devices. Using first-principles calculations, we predict a remarkable strain-induced enhancement of second-harmonic generation (SHG) in the high-performance 2D semiconductors Bi\(_2\)O\(_2\)X (X = S, Se, Te). The SHG susceptibilities of Bi\(_2\)O\(_2\)X under strain are on the order of 1~nm/V, rivalling the highest values reported among 2D materials. This giant SHG response originates from gauge-invariant geometric quantities, including the quantum metric, shift vector, and triple phase product. The strain also induces a bandgap variation in Bi\(_2\)O\(_2\)X. Intriguingly, in Bi\(_2\)O\(_2\)Te, strain-induced bandgap tuning drives a transition from a semiconductor to a half-metal, and ultimately to a polar metal. Our findings present a unique platform that combines strain-tunable bandgap engineering with exceptional NLO properties, while also highlighting the crucial role of quantum geometry in enhancing SHG.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
8 pages, 4 figures
Networks of neural networks: more is different
New Submission | Disordered Systems and Neural Networks (cond-mat.dis-nn) | 2025-01-29 20:00 EST
Elena Agliari, Andrea Alessandrelli, Adriano Barra, Martino Salomone Centonze, Federico Ricci-Tersenghi
The common thread behind the recent Nobel Prize in Physics to John Hopfield and those conferred to Giorgio Parisi in 2021 and Philip Anderson in 1977 is disorder. Quoting Philip Anderson: "more is different". This principle has been extensively demonstrated in magnetic systems and spin glasses, and, in this work, we test its validity on Hopfield neural networks to show how an assembly of these models displays emergent capabilities that are not present at a single network level. Such an assembly is designed as a layered associative Hebbian network that, beyond accomplishing standard pattern recognition, spontaneously performs also pattern disentanglement. Namely, when inputted with a composite signal -- e.g., a musical chord -- it can return the single constituting elements -- e.g., the notes making up the chord. Here, restricting to notes coded as Rademacher vectors and chords that are their mixtures (i.e., spurious states), we use tools borrowed from statistical mechanics of disordered systems to investigate this task, obtaining the conditions over the model control-parameters such that pattern disentanglement is successfully executed.
Disordered Systems and Neural Networks (cond-mat.dis-nn), Statistical Mechanics (cond-mat.stat-mech), Mathematical Physics (math-ph)
28 pages, 11 figures
Anisotropic galvanomagnetic effects in single-crystal Fe(001) films elucidated by a phenomenological theory
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Haoran Chen, Zhen Cheng, Yizi Feng, Hongyue Xu, Tong Wu, Chuanhang Chen, Yue Chen, Zhe Yuan, Yizheng Wu
Utilizing the phenomenological theory based on crystal symmetry operation, we have established the complete angular dependencies of the galvanomagnetic effects, encompassing both anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE), for the ferromagnetic films with C4v symmetry. These dependencies were experimentally confirmed via comprehensive angular-mapping of AMR and PHE in single-crystal Fe(001) films at room temperature. We demonstrated that the intrinsic magnetization-induced effects are independent of the field strength by carefully separating the field-induced and magnetization-induced galvanomagnetic effects. Our theoretical and experimental findings highlight the absence of in-plane four-fold angular dependence in PHE, a feature prohibited by the Onsager relation in systems with C4 symmetry. This study affirms that the universal angular dependencies of AMR and PHE in single crystals can be accurately predicted by the conventional phenomenological theory.
Materials Science (cond-mat.mtrl-sci), Other Condensed Matter (cond-mat.other)
32 pages, 6 figures, with supplemental material
Phys. Rev. B 111, 014437 (2025)
Anomalous Landau levels and quantum oscillation in rotation-invariant insulators
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-29 20:00 EST
Jianlong Fu, Chun Yu Weng, Hoi Chun Po
Landau levels in certain models are known to protrude into the zero-field energy gap. These are known as anomalous Landau levels (ALLs). We study whether ALLs can lead to in-gap quantum oscillation in the absence of a zero-field Fermi surface. Focusing on two-dimensional multi-band low-energy models of electrons with continuous rotation symmetry, we show that an effective-band description, akin to the semiclassical treatment of Landau level problems in metals, can be used to predict the Landau level spectrum, including possible ALLs. This description then predicts quantum oscillation for certain insulating models, which we demonstrate through numerical calculations.
Strongly Correlated Electrons (cond-mat.str-el)
10 pages, 4 figures
Reversal of Spin-torque Polarity with Inverting Current Vorticity in Composition-graded Layer at the Ti/W Interface
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Hayato Nakayama, Taisuke Horaguchi, Jun Uzuhashi, Cong He, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuto Yamanoi, Yukio Nozaki
While compositional gradient-induced spin-current generation has been explored, its microscopic mechanisms remain poorly understood. Here, the contribution of polarity of compositional gradient on spin-current generation is explored. A nanoscale compositional gradient, formed by in-situ atomic diffusion of ultrathin Ti and W layers, is introduced between 10-nm-thick W and Ti layers. Spin-torque ferromagnetic resonance in ferromagnetic Ni95Cu5 deposited on this gradient reveals that a moderate compositional gradient suppresses negative spin torque from the spin Hall effect in W. In contrast, reversing the Ti/W stacking order, which inverts the gradient, suppresses positive spin torque from the orbital Hall effect in Ti. These findings suggest that the sign of spin torque is governed by the polarity of compositional gradient, providing a novel strategy for efficient spin-torque generation without relying on materials with strong spin or orbital Hall effect.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
17 pages, 7 figures
Theoretical study of the impact of carrier density screening on Urbach tail energies and optical polarization in (Al,Ga)N quantum well systems
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Robert Finn, Michael O'Donovan, Thomas Koprucki, Stefan Schulz
Aluminium Gallium Nitride ((Al,Ga)N) presents an ideal platform for designing ultra-violet (UV) light emitters across the entire UV spectral range. However, in the deep-UV spectral range (<280 nm) these emitters exhibit very low quantum efficiencies, which in part is linked to the light polarization characteristics of (Al,Ga)N quantum wells (QWs). In this study we provide insight into the degree of optical polarization of (Al,Ga)N QW systems operating across the UV-C spectral range by means of an atomistic, multi-band electronic structure model. Our model not only captures the difference in valence band ordering in AlN and GaN, it accounts also for alloy disorder induced band mixing effects originating from random alloy fluctuations in (Al,Ga)N QWs. The latter aspect is not captured in widely employed continuum based models. The impact of alloy disorder on the electronic structure is studied in terms of Urbach tail energies, which reflect the broadening of the valence band density of states due to carrier localization effects. We find that especially in wider wells, Urbach tail energies are reduced with increasing carrier densities in the well, highlighting that alloy disorder induced carrier localization effects in (Al,Ga)N QWs are also tightly linked to electrostatic built-in fields. Our calculations show that for QWs designed to emit at the longer wavelength end of the UV-C spectrum, carrier density and well width are of secondary importance for their light emission properties, meaning that one observes mainly transverse electrical polarization. However, for (Al,Ga)N QWs with high Al contents, we find that both well width and carrier density will impact the degree of optical polarization. Our calculations suggest that wider wells will increase the degree of optical polarization and may therefore be a viable option to improve the light extraction efficiency in deep UV light emitters.
Materials Science (cond-mat.mtrl-sci)
14 pages, 9 figures
Original Ultra-hard Orthorhombic Carbon allotropes C8 with lonsdaleite-type lon topology: Crystallographic and DFT investigations
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
The lon topology inherent to lonsdaleite C4 hexagonal diamond is shown to characterize three original carbon allotropes C8 in the orthorhombic system with irregular orientations of the C4 tetrahedra. The octacarbon stoichiometries were devised from crystal structure engineering and identified close to lonsdaleite from density functional theory (DFT) based calculations of ground state structures and energy derived physical properties. Characterized with high densities, the three allotropes are identified with ultra hard with hardness magnitudes close and superior to lonsdaleite. Dynamically, all three allotropes were found stable with positive frequencies revealed from their phonons band structures with specific heat CV = f(T) calculated curves close to diamond experimental values from literature.
Materials Science (cond-mat.mtrl-sci)
18 pages; 4 Figures; 3 tables
Multi-types of Instability Process of Periodic Orbits in Nonlinear Chains
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-01-29 20:00 EST
Weicheng Fu, Zhen Wang, Yong Zhang, Hong Zhao
Nonlinear normal modes are periodic orbits that survive in nonlinear many-body Hamiltonian systems, and their instability plays a key role in the system's relaxation dynamics. We investigate here the instability of the \(\pi/3\)-mode in the Fermi-Pasta-Ulam-Tsingou-\(\alpha\) chain with fixed boundary conditions. We find that three types of bifurcations -- period-doubling, tangent, and Hopf bifurcations -- coexist in this system, each driving instability at specific reduced wave-number \(\tilde{k}\). Our analysis reveals a universal scaling law for the instability time \(\mathcal{T} \propto (\lambda - \lambda_{\rm c})^{-1/2}\), independent of bifurcation types and models, where the critical perturbation strength \(\lambda_{\rm c}\) depends on \(\tilde{k}\) via \(\lambda_{\rm c} \propto (\tilde{k} - \tilde{k}_{\rm c})\), with \(\tilde{k}_{\rm c}\) varying across bifurcations. We also observe a double instability phenomenon for certain system sizes. These results provide new insights into the relaxation and thermalization dynamics in many-body systems, with broad implications for nonlinear and non-equilibrium statistical physics.
Statistical Mechanics (cond-mat.stat-mech)
7 pages, 5 figures
Quantum fluctuations can enhance or reduce positional uncertainty at finite temperature
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-01-29 20:00 EST
The uncertainty principle guarantees a non-zero value for the positional uncertainty, \(\left\langle\Delta x^2\right\rangle > 0\), even without thermal fluctuations. This implies that quantum fluctuations inherently enhance positional uncertainty at zero temperature. A natural question then arises: what happens at finite temperatures, where the interplay between quantum and thermal fluctuations may give rise to complex and intriguing behaviors? To address this question, we systematically investigate the positional uncertainty, \(\left\langle\Delta x^2\right\rangle\), of a particle in equilibrium confined within a nonlinear potential of the form \(V(x) \propto x^a\), where \(a = 2, 4, 6, \dots\) represents an even exponent. Using path integral Monte Carlo simulations, we calculate \(\left\langle\Delta x^2\right\rangle\) in equilibrium as a function of the thermal de Broglie wavelength \(\Lambda\). Interestingly, for large values of \(a\), \(\left\langle\Delta x^2\right\rangle\) exhibits a non-monotonic dependence on \(\Lambda\): it initially decreases with increasing \(\Lambda\) at small \(\Lambda\) but increases at larger \(\Lambda\). To further understand this behavior, we employ a semiclassical approximation, which reveals that quantum fluctuations can reduce positional uncertainty for small \(\Lambda\) when the nonlinearity of the potential is sufficiently strong. Finally, we discuss the potential implications of this result for many-body phenomena driven by strong nonlinear interactions, such as glass transitions, where the transition densities exhibit a similar non-monotonic dependence on \(\Lambda\).
Statistical Mechanics (cond-mat.stat-mech), Disordered Systems and Neural Networks (cond-mat.dis-nn), Quantum Gases (cond-mat.quant-gas)
7 pages, 5 figures
Active chiral rotors: hydrodynamics and chemotaxis
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-29 20:00 EST
R. Maity, Snigdha Thakur, P. S. Burada
An active chiral rotor is a spherical object that can generate chiral flows in a fluid by rotating about an axis. For example, if the flow around the upper hemisphere of the chiral rotor is in a clockwise direction, then the flow in the lower hemisphere is in the anti-clockwise direction, and vice versa. In this paper, we aim to study the combined behaviour of hydrodynamically interacting chiral rotors in the presence of an external chemical gradient. While a single isolated rotor is stationary in a fluid, a pair of rotors can move in linear or circular paths as they hydrodynamically interact with each other. It is observed that the emergent linear or circular trajectories depend on the type of rotors and the orientation of their rotation axes. The dynamics of the rotors are altered in a more complex environment, such as in an external chemical field. Interestingly, we observe two types of motion: chemotaxis and anti-chemotaxis. While in the anti-chemotaxis case, both rotors are driving away from the target, in the chemotaxis case, one of the rotors successfully reaches the chemical target. This study helps to understand the collective behavior of self-propelled microorganisms and artificial swimmers.
Soft Condensed Matter (cond-mat.soft), Biological Physics (physics.bio-ph)
Two-dimensional spectroscopy of bosonic collective excitations in disordered many-body systems
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-29 20:00 EST
Alex Gómez Salvador, Ivan Morera, Marios H. Michael, Pavel E. Dolgirev, Danica Pavicevic, Albert Liu, Andrea Cavalleri, Eugene Demler
We present a novel theoretical approach for computing and analyzing two-dimensional spectroscopy of bosonic collective excitations in disordered many-body systems. Specifically, we employ the Keldysh formalism to derive the nonlinear response and obtain two-dimensional spectroscopy maps with particular emphasis on the rephasing sector, which allows to disentangle different sources of broadening. Our many-body approach successfully distinguishes elastic and inelastic scattering mechanisms contributing to the excitation linewidth. Additionally, using a non-perturbative conserving approach, we demonstrate that the echo peak exhibits a universal asymmetric shape in the sole presence of static disorder, a feature that remains robust against quantum fluctuations. This is in stark contrast to the standard theory based on isolated two-level systems, which fails to account for the dispersive nature of excitations and the interactions between different momentum components.
Strongly Correlated Electrons (cond-mat.str-el), Superconductivity (cond-mat.supr-con), Quantum Physics (quant-ph)
14 + 4 pages, 9 + 2 figures
Ultra-strong coupling of two ferromagnets via Meissner currents
New Submission | Superconductivity (cond-mat.supr-con) | 2025-01-29 20:00 EST
V. M. Gordeeva, G. A. Bobkov, A. M. Bobkov, I. V. Bobkova, Tao Yu
In this work, we study the magnetization dynamics in a ferromagnet/insulator/ferromagnet trilayer sandwiched between two superconductors (S/F/I/F/S heterostructure). It is well-known that a conceptually similar S/F/S system is a platform for implementing ultra-strong magnon-photon coupling. Here, we demonstrate that in such S/F/I/F/S heterostructure, ultra-strong magnon-magnon coupling also appears. The strength of this interaction is many times greater than the strength of the usual dipole-dipole interaction. It is mediated via Meissner currents excited in the superconductor layers by the magnon stray fields. The strength of the magnon-magnon coupling is anisotropic, and its anisotropy is opposite to the anisotropy of the magnon-photon coupling, which allows them to be separated. Both couplings become much stronger when the temperature drops below the critical temperature of the superconductor layers. It enables the implementation of an efficient tuning of the wavenumber in the S/F/I/F/S heterostructures controlled by temperature in a wide range of frequencies. Overall, the rich and tunable spectrum of S/F/I/F/S multilayers opens broad prospects for their application in magnonics.
Superconductivity (cond-mat.supr-con), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Bi-self-trapping of excitons via the long-living phonon mode and their superfluorescent markers
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Understanding the origin of the system response offers guidance for designing single-component material devices with required properties. A notable phenomenon of room-temperature superfluorescence recently observed in hybrid perovskites at high concentrations of excitations lacks of comprehensive theoretical framework. Addressing this gap necessitates a discussion grounded in non-linear and multiparticle theories. In this study, we offer the two-step mechanism: formation of two self-trapped excitons entangled via the same long-living phonon mode, and their rearrangement into a superradiating mirror symmetric configuration. Based on the semiclassical equations of motion we examine the criteria for the high-temperature self-trapping and bi-self trapping of excitons. Our findings indicate that the self-trapped excitons are described by the stable phase-locked steadystate solution of the equations of motion, and at elevated exciton concentrations, they compete with the bi-self-trapped excitons. The latter is described by the Dicke model and is thus responsible for the generation of the superfluorescent spectral peak. The obtained theoretical spectra are in good agreement with the experimental observation.
Materials Science (cond-mat.mtrl-sci), Optics (physics.optics), Quantum Physics (quant-ph)
Unconventional resistive switching in dense Ag-based nanowire networks with brain-inspired perspectives
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Juan I. Diaz Schneider, Cynthia P. Quinteros, Eduardo D. Martínez, Pablo E. Levy
We report an unconventional resistive switching effect on high-density self-assembled Ag-nanowire networks tailored by a fuse-like operation. We propose a mechanism to rationalize the observed phenomenology by analyzing the electrical signatures before and after such a fusing. The explanation allows reconciling the results obtained in similar systems early adopted as transparent electrodes and the more recent attempts to use this type of substrate for in-materia computational operations. In addition to the usual analog nature of the available resistance states and the ability to tune internal weights, we show that these networks' sparsity and non-linear behavior are also attributes. Thus, the formerly exhibited nanowires' abilities to code synaptic behavior are complemented by neuronal features upon properly tuning the network density and the applied electrical protocol.
Materials Science (cond-mat.mtrl-sci), Disordered Systems and Neural Networks (cond-mat.dis-nn), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Machine-learning semi-local exchange-correlation functionals for Kohn-Sham density functional theory of the Hubbard model
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-29 20:00 EST
Eoghan Cronin, Rajarshi Tiwari, Stefano Sanvito
The Hubbard model provides a test bed to investigate the complex behaviour arising from electron-electron interaction in strongly-correlated systems and naturally emerges as the foundation model for lattice density functional theory (DFT). Similarly to conventional DFT, lattice DFT computes the ground-state energy of a given Hubbard model, by minimising a universal energy functional of the on-site occupations. Here we use machine learning to construct a class of scalable `semi-local' exchange-correlation functionals with an arbitrary degree of non-locality for the one-dimensional spinfull Hubbard model. Then, by functional derivative we construct an associated Kohn-Sham potential, that is used to solve the associated Kohn-Sham equations. After having investigated how the accuracy of the semi-local approximation depends on the degree of non-locality, we use our Kohn-Sham scheme to compute the polarizability of linear chains, either homogeneous or disordered, approaching the thermodynamic limit. approaching the thermodynamic limit.
Strongly Correlated Electrons (cond-mat.str-el)
15 pages, 14 figures
The spin-orbital Kitaev model: from kagome spin ice to classical fractons
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-29 20:00 EST
Weslei B. Fontana, Fabrizio G. Oliviero, Rodrigo G. Pereira, Willian M. H. Natori
We study an exactly solvable spin-orbital model that can be regarded as a classical analogue of the celebrated Kitaev honeycomb model and describes interactions between Rydberg atoms on the ruby lattice. We leverage its local and nonlocal symmetries to determine the exact partition function and the static structure factor. A mapping between \(S=3/2\) models on the honeycomb lattice and kagome spin Hamiltonians allows us to interpret the thermodynamic properties in terms of a classical kagome spin ice. Partially lifting the symmetries associated with line operators, we obtain a model characterized by immobile excitations, called classical fractons, and a ground state degeneracy that increases exponentially with the length of the system. We formulate a continuum theory that reveals the underlying gauge structure and conserved charges. Extensions of our theory to other lattices and higher-spin systems are suggested.
Strongly Correlated Electrons (cond-mat.str-el)
13 pages, 8 figures
Universality of the complete-graph Potts model with \(0< q \leq 2\)
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-01-29 20:00 EST
Zirui Peng, Sheng Fang, Hao Hu, Youjin Deng
Universality is a fundamental concept in modern physics. For the \(q\)-state Potts model, the critical exponents are merely determined by the order-parameter symmetry \(S_q\), spatial dimensionality and interaction range, independent of microscopic details. In a simplest and mean-field treatment--i.e., the Potts model on complete graph (CG), the phase transition is further established to be of percolation universality for the range of \(0 < q <2\). By simulating the CG Potts model in the random-cluster representation, we numerically demonstrate such a hyper-universality that the critical exponents are the same for \(0< q <2\) and, moreover, the Ising system (\(q = 2\)) exhibits a variety of critical geometric properties in percolation universality. On the other hand, many other universal properties in the finite-size scaling (FSS) theory, including Binder-like ratios and distribution function of the order parameter, are observed to be \(q\)-dependent. Our finding provides valuable insights for the study of critical phenomena in finite spatial dimensions, particularly when the FSS theory is utilized.
Statistical Mechanics (cond-mat.stat-mech), Computational Physics (physics.comp-ph)
A sturdy spin-momentum locking in a chiral organic superconductor
New Submission | Superconductivity (cond-mat.supr-con) | 2025-01-29 20:00 EST
Takuro Sato, Hiroshi Goto, Hiroshi M. Yamamoto
Among noncentrosymmetric structures, chirality has recently been recognized as a novel source of asymmetrical charge/spin transports as exemplified by electrical magnetochiral anisotropy (EMChA) and chirality-induced spin selectivity. Although similar bulk-charge rectification and Rashba-Edelstein effect in polar systems are quantitively reproducible by theory based on the electronic band structures, the relevance of band parameters in chiral effects remains elusive. Here, by working with a chiral organic superconductor, we experimentally demonstrate a gigantic EMChA and large superconducting diode effect, both of which are difficult to be explained solely by its band parameters. A two-critical-current signature and an enhanced critical field suggested triplet-mixed Cooper pairs with anomalously enhanced spin-orbit coupling above atomic limit. Our results clearly highlight a unique spin-momentum locking with large stiffness beyond the expectation, suggesting an unknown driving force for spin polarization inherent to chirality.
Superconductivity (cond-mat.supr-con), Materials Science (cond-mat.mtrl-sci), Strongly Correlated Electrons (cond-mat.str-el)
8 pages, 4 figures
The Effect of the Non-Abelian Quantum Metric on Superfluidity
New Submission | Superconductivity (cond-mat.supr-con) | 2025-01-29 20:00 EST
Kai Chen, Bishnu Karki, Pavan Hosur
The quantum geometric tensor, which encodes the full geometric information of quantum states in projective Hilbert space, plays a crucial role in condensed matter physics. In this work, we examine the effect of the non-Abelian quantum metric -- the real part of the non-Abelian quantum geometric tensor -- on the superfluid weight in time-reversal symmetric systems. For conventional \(s\)-wave pairing, we demonstrate that the superfluid weight includes a contribution proportional to the trace of the non-Abelian quantum metric. Notably, this contribution remains significant even when the total Chern number of a set of degenerate bands is zero and can exceed the conventional contribution, as confirmed using lattice models. Ab initio density functional theory (DFT) calculations for MoS\(_2\) and TiSe\(_2\) further corroborate these findings, revealing that the non-Abelian quantum metric accounts for up to 20% of the superfluid weight in MoS\(_2\) and 50% in TiSe\(_2\). Our results provide new insights into the nontrivial relationship between the geometric properties of quantum states and superconductivity, opening avenues for further exploration in topological and superconducting materials.
Superconductivity (cond-mat.supr-con), Materials Science (cond-mat.mtrl-sci), Strongly Correlated Electrons (cond-mat.str-el)
Glassforming liquid crystalline equimolar mixtures of MHPOBC and fluorinated compounds -- structural, optical, and dielectric properties
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-29 20:00 EST
Aleksandra Deptuch, Anna Paliga, Anna Drzewicz, Michał Czerwiński, Ewa Juszyńska-Gałązka
Three liquid crystalline equimolar mixtures are formulated, each containing the MHPOBC compound and the homolog from the 3FmHPhF6 series with m = 4, 5 or 6. The properties of the mixtures are investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray diffraction, electro-optic measurements, and UV-Vis-NIR and dielectric spectroscopies. In all mixtures, the smectic A, smectic C, and smectic C\(_A\)phases are observed. Each mixture can be supercooled and forms the glass of smectic C\(_A\)at 225-238 K. The glass transition temperature decreases with the increasing C\(_m\)H\(_{2m}\) chain length in the 3FmHPhF6 molecule. The tilt angle in the smectic C\(_A\)phase reaches 36.5-37.5°. The selective reflection of light in the visible and near-infrared spectral ranges is observed, with a strong dependence of the reflected light's wavenumber on temperature.
Soft Condensed Matter (cond-mat.soft)
Emergent collective behavior of cohesive, aligning particles
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-29 20:00 EST
Collective behavior is all around us, from flocks of birds to schools of fish. These systems are immensely complex, which makes it pertinent to study their behavior through minimal models. We introduce such a minimal model for cohesive and aligning self-propelled particles in which group cohesion is established through additive, non-reciprocal torques. These torques cause constituents to effectively turn towards one another. We additionally incorporate an alignment torque, which competes with the cohesive torque in the same spatial range. By changing the strength and range of these torque interactions, we uncover six states which we distinguish via their static and dynamic properties: a disperse state, a multiple worm state, a line state, a persistent worm state, a rotary worm state, and an aster state. Their occurrence strongly depends on initial conditions and stochasticity, so the model exhibits multistabilities. A number of the states exhibit collective dynamics which are reminiscent of those seen in nature.
Soft Condensed Matter (cond-mat.soft)
Probing quantum many-body dynamics using subsystem Loschmidt echos
New Submission | Quantum Gases (cond-mat.quant-gas) | 2025-01-29 20:00 EST
Simon Karch, Souvik Bandyopadhyay, Zheng-Hang Sun, Alexander Impertro, SeungJung Huh, Irene Prieto Rodríguez, Julian F. Wienand, Wolfgang Ketterle, Markus Heyl, Anatoli Polkovnikov, Immanuel Bloch, Monika Aidelsburger
The Loschmidt echo - the probability of a quantum many-body system to return to its initial state following a dynamical evolution - generally contains key information about a quantum system, relevant across various scientific fields including quantum chaos, quantum many-body physics, or high-energy physics. However, it is typically exponentially small in system size, posing an outstanding challenge for experiments. Here, we experimentally investigate the subsystem Loschmidt echo, a quasi-local observable that captures key features of the Loschmidt echo while being readily accessible experimentally. Utilizing quantum gas microscopy, we study its short- and long-time dynamics. In the short-time regime, we observe a dynamical quantum phase transition arising from genuine higher-order correlations. In the long-time regime, the subsystem Loschmidt echo allows us to quantitatively determine the effective dimension and structure of the accessible Hilbert space in the thermodynamic limit. Performing these measurements in the ergodic regime and in the presence of emergent kinetic constraints, we provide direct experimental evidence for ergodicity breaking due to fragmentation of the Hilbert space. Our results establish the subsystem Loschmidt echo as a novel and powerful tool that allows paradigmatic studies of both non-equilibrium dynamics and equilibrium thermodynamics of quantum many-body systems, applicable to a broad range of quantum simulation and computing platforms.
Quantum Gases (cond-mat.quant-gas), Statistical Mechanics (cond-mat.stat-mech), Atomic Physics (physics.atom-ph), Quantum Physics (quant-ph)
Upper critical field and colossal spin valve analogy in normal metal-superconductor-normal metal trilayers
New Submission | Superconductivity (cond-mat.supr-con) | 2025-01-29 20:00 EST
Kelsey B. Robbins, Pukar Sedai, Alexandra J. Howzen, Robert M. Klaes, Reza Loloee, Norman O. Birge, Nathan Satchell
The role of spin orbit interaction in superconducting proximity effect is an area of intense research effort. Recent theoretical and experimental works investigate the possible role of spin-orbit interaction in generating spin-triplet pair correlations. In this work, we present an experimental survey of thin normal metal-superconductor-normal metal trilayers with Nb superconductor and Al, Ti, Cu, Pt, Ta, and Au normal metals, along with single layers of Nb as reference. We aim to probe the role of spin-orbit interaction and resistivity on the normal metal proximity effect through measurements of the upper critical field. We find that the upper critical fields of the trilayers are lower than that of a single layer Nb reference sample, and that the trilayers with higher resistivity metals, Ti, Pt, and Ta, behave as 2-dimensional superconductors. We also find that compared to single layer Nb films, the trilayers show a greater suppression of critical temperature during rotation from in-plane to out-of-plane applied magnetic field. This suppression of critical temperature under field rotation is analogous to the colossal spin valve effect that can be achieved in systems with ferromagnetic materials, however in our trilayers only orbital contributions to the suppression are present.
Superconductivity (cond-mat.supr-con), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
9 pages, 4 figures, 1 table
Numerical insights on the volume phase transition of thermoresponsive hollow microgels
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-29 20:00 EST
Leah Rank, Emanuela Zaccarelli
Hollow microgels, consisting of a pNIPAM polymer network with a central cavity, have significant potential due to their tunable softness and encapsulation capabilities. Using molecular dynamics simulations, we thoroughly characterise the swelling behaviour of neutral hollow microgels across the Volume Phase Transition (VPT) upon varying crosslinker concentration, shell thickness, and size. In particular, we examine in detail the onset of cavity filling and its relation to the VPT, detecting the presence of a discontinuity in the radius of gyration of the microgels, if an appropriate balance between shell stiffness and thermoresposiveness is reached. The discontinuity is, however, absent in the behaviour of the hydrodynamic radius, in agreement with experimental observations. We then test our numerical model by direct comparison of form factors with available measurements in the literature and also establish a minimal-size, stable hollow microgel for future computationally feasible bulk investigations. Overall, our findings provide valuable insights into the fundamental swelling properties of hollow microgels that can be useful to control the opening and closing of the cavity for application purposes.
Soft Condensed Matter (cond-mat.soft)
14 pages, 10 figures
Enhanced Thermoelectric Performance through Site-Specific Doping in Tetragonal Cu\(_{2}\)S: A First-Principles Study
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
This work investigates how site-specific doping can enhance the thermoelectric performance of tetragonal Cu\(_{2}\)S using Density functional Theory and Projected Atomic Orbital Framework for Electronic Transport. We address the gap in current research, where most doping studies focus on the high-temperature cubic polymorph, leaving the tetragonal structure underexplored. By substituting Cu with Li, Na, or Mg, as well as partially replacing S with Se or Te, we systematically examine changes in electronic structure and transport properties. Our results reveal that cation-site doping can strongly shift the Fermi level. In particular, Li doping enhances the power factor (\(\sigma S^2\)) by optimizing carrier concentrations and band-edge alignments, whereas Mg, due to its divalent nature, offers a higher carrier density but requires careful balancing to maintain a large Seebeck coefficient. On the anion side, substituting heavier chalcogens (Se or Te) reshapes the valence bands and subtly shifts the Fermi level, yielding moderate improvements in both electrical conductivity and Seebeck coefficient. These doping-induced alterations, captured through transport calculations, demonstrate a clear route for tailoring the interplay between conductivity and thermal transport toward potentially high figure-of-merit values. Overall, the findings highlight the importance of site specificity in doping strategies for tetragonal Cu\(_{2}\)S, showing that judicious choice of dopant elements and concentrations can significantly improve key thermoelectric metrics. Such insights provide a foundation for experimental validation and further development of Cu\(_{2}\)S-based materials for mid- to high-temperature thermoelectric applications.
Materials Science (cond-mat.mtrl-sci)
Quantitative study on anomalous Nernst effect in Co thin films by laser irradiation
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Soichiro Mochizuki, Itaru Sugiura, Tetsuya Narushima, Teruo Ono, Takuya Satoh, Kihiro T. Yamada
The anomalous Nernst effect (ANE) generates electromotive forces transverse to temperature gradients and has attracted much attention for potential applications into novel thermoelectric power generators. ANE efficiency is generally characterized by uniform temperature gradients in a steady state prepared by heaters. However, although focusing laser beams on a magnetic film can form much larger temperature gradients, the laser irradiation method has not been sufficiently considered for quantifying the ANE coefficient due to the difficulty in estimating the localized in-homogeneous temperature gradients. In this study, we present a quantitative study of ANE in Ru(5 nm)/Co(\(t_{\mathrm{Co}}\)) (\(t_{\mathrm{Co}}\) = 3, 5, 7, 10, 20, 40, and 60 nm) bilayers on sapphire (0001) substrates by combining a laser irradiation approach with finite element analysis of temperature gradients under laser excitation. We find that the estimated ANE coefficients are consistent with previously reported values and one independently characterized using a heater. Our results also reveal the advantages of the laser irradiation method over the conventional method using heaters. Intensity-modulated laser beams can create ac temperature gradients as large as approximately 10\(^3\) K/mm at a frequency of tens of kilohertz in a micrometer-scale region.
Materials Science (cond-mat.mtrl-sci)
25 pages, 10 figures. 1 table
Low-temperature magnetic behaviour on the triangular lattice in hexagonal Ba\(_3\)Tb(BO\(_3\))\(_3\)
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-29 20:00 EST
Nicola Kelly, Manh Duc Le, Denis Sheptyakov, Camilla Tacconis, Cheng Liu, Gavin Stenning, Peter Baker, Siân Dutton
The hexagonal polymorph of Ba\(_3\)Tb(BO\(_3\))\(_3\) contains Tb\(^{3+}\) ions on a quasi-2D triangular lattice, resulting in geometric magnetic frustration. Powder samples of Ba\(_3\)Tb(BO\(_3\))\(_3\) have been investigated using specific heat, powder neutron diffraction (PND), inelastic neutron scattering (INS) and muon-spin relaxation spectroscopy (\(\mu\)SR). No long-range magnetic ordering is observed down to the lowest measured temperatures of 75 mK in PND and specific heat data and 1.5 K in the \(\mu\)SR data. Modelling the INS spectrum using a point charge model suggests that the ground state is a singlet with a low-lying doublet on each of the two crystallographically independent Tb\(^{3+}\) sites and that both the Tb ions display weak XY single-ion anisotropy.
Strongly Correlated Electrons (cond-mat.str-el)
22 pages, 7 figures
Inhomogeneous Electric Fields for Precise Control and Displacement of Polar Textures
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Fernando Gómez-Ortiz, Louis Bastogne, He Xu, Philippe Ghosez
Since the discovery of polar topological textures, achieving efficient control and manipulation of them has emerged as a significant challenge for their integration into nanoelectronic devices. In this study, we use second principles molecular dynamic simulations to demonstrate the precise and reversible control of domain arrangements stabilizing diverse polarization textures through the application of various inhomogeneous electric fields. Furthermore, we conduct an in-depth study of ferroelectric domain motion under such fields, revealing features consistent with creep dynamics and establishing an upper limit for their propagation speed. Notably, our findings show that domain walls exhibit an asymmetric inertial response, present at the onset of the dynamics but absent during their cessation. These findings provide valuable insights into the dynamic behavior of polar textures, paving the way for the development of high-speed, low-power nanoelectronic applications.
Materials Science (cond-mat.mtrl-sci)
A Variational Theory for Soft Shells
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-29 20:00 EST
Andre M. Sonnet, Epifanio G. Virga
Three general modes are distinguished in the deformation of a thin shell; these are stretching, drilling, and bending. Of these, the drilling mode is the one more likely to emerge in a soft matter shell (as compared to a hard, structural one), as it is ignited by a swerve of material fibers about the local normal. We propose a hyperelastic theory for soft shells, based on a separation criterion that envisages the strain-energy density as the sum of three independent pure measures of stretching, drilling, and bending. Each individual measure is prescribed to vanish on all other companion modes. The result is a direct, second-grade theory featuring a bending energy quartic in an invariant strain descriptor that stems from the polar rotation hidden in the deformation gradient (although quadratic energies are also appropriate in special cases). The proposed energy functional has a multi-well character, which fosters cases of soft elasticity (with a continuum of ground states) related to minimal surfaces.
Soft Condensed Matter (cond-mat.soft)
Mechanism of Oxygen Reduction via Chemical Affinity in NiO/SiO2 Interfaces Irradiated with keV Energy Hydrogen and Helium Ions for Heterostructure Fabrication
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Mario Mery, Claudio Gonzalez-Fuentes, Igor Stankovic, Jorge M. Nuñez, Jorge E. Valdés, Myriam H Aguirre, Carlos García
Low-energy light ion beams are an essential resource in lithography for nanopatterning magnetic materials and interfaces due to their ability to modify the structure and properties of metamaterials. Here we create ferromagnetic/non-ferromagnetic heterostructures with a controlled layer thickness and nanometer-scale precision. For this, hydrogen ion (H+) irradiation is used to reduce the antiferromagnetic nickel oxide (NiO) layer into ferromagnetic Ni with lower fluence than in the case of helium ion (He+) irradiation. Our results indicate that H+ chemical affinity with oxygen is the primary mechanism for efficient atom remotion, as opposed to He+ irradiation, where the chemical affinity for oxygen is negligible.
Materials Science (cond-mat.mtrl-sci)
Nanoscale Horizons, 2025
Nanoparticle simulations of logarithmic creep and microprestress relaxation in concrete and other disordered solids
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Enrico Masoero, Giovanni Di Luzio
Bažant's microprestress theory relates the logarithmic basic creep of concrete to power-law relaxation of heterogeneous eigenstresses at the nanoscale. However, the link between material chemistry, nanostructure, and microprestress relaxation, is not understood. To approach this, we use a simple model of harmonically interacting, packed nanoparticles, relaxing with and without external stress. Microprestresses are related to per-particle virial stress heterogeneities. Simulation results show that logarithmic creep and power-law microprestress relaxation emerge from generic deformation kinetics in disordered systems, which can occur in various materials and at various scales. When the interactions are matched to some mechanical properties of C--S--H at the 100 nm scale, the predicted microprestresses have similar magnitude as in Bažant's theory. The ability of our simulations to quantitatively link stress relaxation with nanostructure and chemistry-dependent interactions, provides a pathway to better characterise, extrapolate, and even engineer the creep behaviour of traditional and new concretes.
Materials Science (cond-mat.mtrl-sci)
Cement and Concrete Research, volume 137, article number 106181, year 2020
New Method for Robust Critical Analysis of Magnetic Systems
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-29 20:00 EST
Harish Chandr Chauhan, Umesh C. Roy, Shovan Dan, A. Thamizhavel, Pintu Das
Here, we present new methods for critical analysis to determine the range of exchange interaction(s) and appropriate values of critical exponents for different magnetic systems. From computational and experimental investigations of magnetic behavior of Ni and Gd, we show that the critical behavior remains the same on either side of transition temperature. Using our proposed method of analysis for Gd, we find a critical role of competing interactions where the local electron moments follow 3D Ising type short-range interactions whereas the itinerant electron moments constitute mean-field type long-range RKKY interaction.
Strongly Correlated Electrons (cond-mat.str-el)
Interlayer Hopping between Surface Mott Insulator and Bulk Band Insulator in layered 1T-TaS_{2}
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Zijian Lin, Jie Li, Xiaodong Cao, Jingjing Gao, Xuan Luo, Yuping Sun, Yi Lu, Nanlin Wang, Jiandong Guo, Xuetao Zhu
In condensed matter physics, various mechanisms give rise to distinct insulating phases. The competition and interplay between these phases remain elusive, even for the seemingly most distinguishable band and Mott insulators. In multilayer systems, such interplay is mediated by interlayer hopping, which competes with the Coulomb repulsion to determine the nature of insulators. The layered compound 1T-TaS_{2} provides an ideal platform for investigating this phenomenon, as it naturally hosts coexisting Mott and band insulating states. However, distinguishing these distinct insulating states and characterizing the evolution remain challenging. In this study, we employ a dual approach utilizing surface-sensitive High-Resolution Electron Energy Loss Spectroscopy (HREELS) and bulk-sensitive Fourier-transform Infrared Spectroscopy (FTIR) to investigate the electronic excitation spectrum of 1T-TaS_{2}. Our methodology effectively identifies the features originating from the Mott and band insulators by analyzing the differences in their bulk and surface spectral weights, along with their energy distinctions. Based on the previous identification, we further investigate the evolution of insulating state features in the homostructure as they are modulated by temperature. The measurements and Dynamical Mean-Field Theory (DMFT) calculations suggest that the softening and broadening of Hubbard excitations in the Mott state with increasing temperature result from enhanced interlayer hopping between the Mott and band insulators.
Materials Science (cond-mat.mtrl-sci), Strongly Correlated Electrons (cond-mat.str-el)
Self-induced Josephson oscillations and self-trapping in a supersolid dipolar quantum gas
New Submission | Quantum Gases (cond-mat.quant-gas) | 2025-01-29 20:00 EST
Beatrice Donelli, Nicolò Antolini, Giulio Biagioni, Marco Fattori, Andrea Fioretti, Carlo Gabbanini, Massimo Inguscio, Luca Tanzi, Giovanni Modugno, Augusto Smerzi, Luca Pezzè
The Josephson effect characterizes superfluids and superconductors separated by a weak link, the so-called Josephson junction. A recent experiment has shown that Josephson oscillations can be observed also in a supersolid, where the weak link is not due to an external barrier, but is self-induced by interparticle interactions. Here we show theoretically that supersolids -- despite their self-induced character -- feature all the standard properties of bosonic Josephson junction arrays, including macroscopic quantum self-trapping. We focus on the harmonically trapped dipolar supersolids of interest for current experiments, and show that they can be described with a generalized Josephson model that takes into account spatial inhomogeneities. Our work shades new light on the dynamics of supersolids and opens the way to the study of a novel class of Josephson junctions.
Quantum Gases (cond-mat.quant-gas), Quantum Physics (quant-ph)
9 pages, 5 figures
Phase-field modeling of radiation-induced composition redistribution: An application to additively manufactured austenitic Fe-Cr-Ni
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-29 20:00 EST
Sourabh Bhagwan Kadambi, Daniel Schwen, Jia-Hong Ke, Lingfeng He, Andrea M. Jokisaari
Multicomponent alloys undergoing irradiation damage develop radiation-induced composition redistribution at point defect sinks such as grain boundaries (GBs) and dislocations. Such redistribution results in undesired changes to their mechanical behavior and corrosion resistance. Additively manufactured alloys proposed for future nuclear applications are expected to demonstrate a distinct response to irradiation owing to their unique microstructure with as-solidified dislocation density and chemical microsegregation. To capture the composition redistribution in such systems, we develop a mesoscale model with coupled evolution of atomic and point defect components in the presence of dislocation density, dislocation heterogeneity, and thermodynamic interactions at the GB. The model is parameterized for an FCC Fe-Cr-Ni alloy as a representative system for austenitic stainless steels, and simulations are performed in 1D and 2D as a function of irradiation temperature, dose, dislocation density, and grain size. Radiation-induced segregation (RIS) characterized by Cr depletion and Ni enrichment is predicted at both the GB and the dislocation cell wall, with RIS being lower in magnitude but wider at the cell wall. Strongly biased absorption of self-interstitials by dislocations is found to suppress Ni enrichment but slightly enhance Cr depletion under certain conditions. Thermodynamic segregation at the GB is predicted to be narrower and opposite in sign to RIS for both Cr and Ni. Importantly, non-monotonic segregation is found to occur when both thermodynamic and RIS mechanisms are considered, providing a novel physical interpretation of experimental observations. The model is expected to serve as a key tool in accelerated qualification of irradiated materials.
Materials Science (cond-mat.mtrl-sci)