CMP Journal 2025-02-01
Statistics
Nature Reviews Materials: 1
arXiv: 43
Nature Reviews Materials
Large language models for reticular chemistry
Review Paper | Computer science | 2025-01-31 19:00 EST
Zhiling Zheng, Nakul Rampal, Theo Jaffrelot Inizan, Christian Borgs, Jennifer T. Chayes, Omar M. Yaghi
Reticular chemistry is the science of connecting molecular building units into crystalline extended structures such as metal-organic frameworks and covalent organic frameworks. Large language models (LLMs), a type of generative artificial intelligence system, can augment laboratory research in reticular chemistry by helping scientists to extract knowledge from literature, design materials and collect and interpret experimental data – ultimately accelerating scientific discovery. In this Perspective, we explore the concepts and methods used to apply LLMs in research, including prompt engineering, knowledge and tool augmentation and fine-tuning. We discuss how ‘chemistry-aware’ models can be tailored to specific tasks and integrated into existing practices of reticular chemistry, transforming the traditional ‘make, characterize, use’ protocol driven by empirical knowledge into a discovery cycle based on finding synthesis-structure-property-performance relationships. Furthermore, we explore how modular LLM agents can be integrated into multi-agent laboratory systems, such as self-driving robotic laboratories, to streamline labour-intensive tasks and collaborate with chemists and how LLMs can lower the barriers to applying generative artificial intelligence and data-driven workflows to such challenging research questions as crystallization. This contribution equips both computational and experimental chemists with the insights necessary to harness LLMs for materials discovery in reticular chemistry and, more broadly, materials science.
Computer science, Design, synthesis and processing, Metal-organic frameworks, Scientific data
arXiv
Giant orbital Hall effect due to the bulk states of 3D topological insulators
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
James H. Cullen, Hong Liu, Dimitrie Culcer
The highly efficient torques generated by 3D topological insulators make them a favourable platform for faster and more efficient magnetic memory devices. Recently, research into harnessing orbital angular momentum in orbital torques has received significant attention. Here we study the orbital Hall effect in topological insulators. We find that the bulk states give rise to a sizeable orbital Hall effect that is up to 3 orders of magnitude larger than the spin Hall effect in topological insulators. This is partially because the orbital angular momentum that each conduction electron carries is up to an order of magnitude larger than the $\hbar/2$ carried by its spin. Our results imply that the large torques measured in topological insulator/ferromagnet devices can be further enhanced through careful engineering of the heterostructure to optimise orbital-to-spin conversion.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Chiral cavity control of superconducting diode-like nonlinearities
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Time reversal symmetry breaking is an important piece in controlling nonreciprocal responses which are crucial in advancing the utility of quantum materials in device operations. Here, we propose cavity control of superconducting diode-like nonreciprocities where time reversal breaking is achieved via chirality of the cavity modes. With twisted bilayer graphene (TBG) as an example, we demonstrate the general principles of cavity control of band dispersion and geometry using chiral microwave photons which are valid for modes in a split-ring resonator or for modes emulated on a qubit lattice. In particular, we show that time reversal breaking by chiral modes enables superconducting diode-like nonlinearities in TBG by valley polarized states and their skewed quantum geometry. Strikingly, we find sizeable nonreciprocities at par with those obtained in magnetic field trained TBG Jospephson junction devices. The cavity control of superconducting nonreciprocities offers non-invasive means of exploring new functionalities in quantum circuits with in-situ implementation. This can serve as an important contribution to the toolbox for nonreciprocal models in circuit quantum electrodynamics to be harnessed for quantum computing and sensing.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Superconductivity (cond-mat.supr-con)
Athermal creep deformation of ultrastable amorphous solids
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-31 20:00 EST
Pinaki Chaudhuri, Ludovic Berthier, Misaki Ozawa
We numerically investigate the athermal creep deformation of amorphous materials having a wide range of stability. The imposed shear stress serves as the control parameter, allowing us to examine the time-dependent transient response through both the macroscopic strain and microscopic observables. Least stable samples exhibit monotonicity in the transient strain rate versus time, while more stable samples display a pronounced non-monotonic S-shaped curve, corresponding to failure by sharp shear band formation. We identify a diverging timescale associated with the fluidization process and extract the corresponding critical exponents. Our results are compared with predictions from existing scaling theories relevant to soft matter systems. The numerical findings for stable, brittle-like materials represent a challenge for theoretical descriptions. We monitor the microscopic initiation of shear bands during creep responses. Our study encompasses creep deformation across a variety of materials ranging from ductile soft matter to brittle metallic and oxide glasses, all within the same numerical framework.
Soft Condensed Matter (cond-mat.soft), Disordered Systems and Neural Networks (cond-mat.dis-nn), Statistical Mechanics (cond-mat.stat-mech)
Mode-resolved transmission functions: an individual Caroli formula
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Hocine Boumrar, Hand Zenia, Mahdi Hamidi
Efficient manipulation of energy at the nanoscale is crucial for advancements in modern computing, energy harvesting, and thermal management. Specifically, controlling quasiparticle currents is critical to these ongoing technological revolutions. This work introduces a novel and physically consistent approach for computing polarization-resolved transmission functions, a crucial element in understanding and controlling energy transport across interfaces. We show that this new method, unlike several previously derived formulations, consistently yields physically meaningful results by addressing the origin of unphysical behavior in other methods. We demonstrate that while multiple decompositions of the transmission function are possible, only there is a unique and unambiguous route to obtaining physically meaningful results. We highlight and critique the arbitrary nature of these alternative decompositions and their associated failures. While developed within the framework of phonon transport, the individual Caroli formula is general and applicable to other fermionic and bosonic quasiparticles, including electrons, and to internal degrees of freedom such as spin and orbital polarization. Through a comparative analysis using a simple model system, we validate the accuracy and reliability of the individual Caroli formula in capturing polarization-specific transmission properties. This new method provides a more accurate understanding of both phonon and electron transport, offering novel ways for optimization of thermoelectric devices and energy-efficient computing technologies.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Monolithic 4H-SiC nanomechanical resonators with high intrinsic quality factors
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
A. Hochreiter, P. Bredol, F. David, B. Demiralp, H. B. Weber, E. M. Weig
We present an extensive study of 4H-SiC nanomechanical resonators electrochemically etched out of a monocrystalline wafer. Combining piezo-driven interferometric determination of the mechanical spectra with scanning-laser-Doppler vibrometry, an unambiguous assignment of resonance peaks to flexural and torsional modes is achieved. The investigation of multiple harmonic eigenmodes of singly and doubly clamped resonators with varying geometry allows for a comprehensive characterization. Excellent intrinsic mechanical quality factors up to $2\times10^5$ are found at room temperature, approaching the thermoelastic limit at eigenfrquencies exceeding 10 MHz. Mechanical stress is essentially absent. Young’s modulus in agreement with literature. These findings are robust under post-processing treatments, in particular atomic layer etching and high-temperature thermal annealing. The resulting on-chip high-quality mechanical resonators represent a valuable technological element for a broad range of applications. In particular, the monolithic architecture meets the requirements of spin-based photonic quantum technologies on the upcoming SiC platform.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Simulating Curved Lipid Membranes Using Anchored Frozen Patches
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-31 20:00 EST
Lipid bilayers often form high-curvature configurations due to self-assembly conditions or certain biological processes. However, particle-based simulations of lipid membranes are predominantly of flat lipid membranes because planar membranes are easily connected over periodic boundary conditions. To simulate a curved lipid membrane, one can simulate an entire vesicle, a cylinder, or a bicelle (disk-like bilayer aggregate). One can also use artificial methods to control curvature, such as applying virtual walls of beads, radial harmonic potentials, or tape up the edges''. These existing methods have limitations due to the method by which curvature is imposed. Herein, we propose an alternative method of introducing arbitrary curvature by anchoring a curved lipid membrane with frozen’’ equilibrated membrane patches. The method presented here is compatible with all particle-based lipid models and easily extended to many geometries. As an example, we simulate curved membranes with DPPC, DOPC, DLPC and DOPE lipids as parameterized by the Martini3 coarse-grained model. This method introduces limited finite-size artifacts, prevents lipid flip-flop at membrane edges, and allows fluctuations of the free membrane center. We provide verification of the method on flat membranes and discussion on extracting shape and per-leaflet quantities (thickness, order parameter) from curved membranes. Curvature produces asymmetric changes in lipid leaflet properties. Finally, we explore the coupled effect of curvature and membrane asymmetry in both number and lipid type. We report the resulting unique morphologies (inducing gel phase, faceting) and behaviors (thickness dependent on adjacent leaflet type) that are accessible with this method.
Soft Condensed Matter (cond-mat.soft), Biological Physics (physics.bio-ph)
12 pages, 10 figures
Bridging statistical mechanics and thermodynamics away from equilibrium: a data-driven approach for learning internal variables and their dynamics
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-01-31 20:00 EST
Weilun Qiu, Shenglin Huang, Celia Reina
Thermodynamics with internal variables is a common approach in continuum mechanics to model inelastic (i.e., non-equilibrium) material behavior. While this approach is computationally and theoretically attractive, it currently lacks a well-established statistical mechanics foundation. As a result, internal variables are typically chosen phenomenologically and lack a direct link to the underlying physics which hinders the predictability of the theory. To address these challenges, we propose a machine learning approach that is consistent with the principles of statistical mechanics and thermodynamics. The proposed approach leverages the following techniques (i) the information bottleneck (IB) method to ensure that the learned internal variables are functions of the microstates and are capable of capturing the salient feature of the microscopic distribution; (ii) conditional normalizing flows to represent arbitrary probability distributions of the microscopic states as functions of the state variables; and (iii) Variational Onsager Neural Networks (VONNs) to guarantee thermodynamic consistency and Markovianity of the learned evolution equations. The resulting framework, called IB-VONNs, is tested on two problems of colloidal systems, governed at the microscale by overdamped Langevin dynamics. The first one is a prototypical model for a colloidal particle in an optical trap, which can be solved analytically, and thus ideal to verify the framework. The second problem is a one-dimensional phase-transforming system, whose macroscopic description still lacks a statistical mechanics foundation under general conditions. The results in both cases indicate that the proposed machine learning strategy can indeed bridge statistical mechanics and thermodynamics with internal variables away from equilibrium.
Statistical Mechanics (cond-mat.stat-mech), Mathematical Physics (math-ph)
Soliquidy: a descriptor for atomic geometrical confusion
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Hagen Eckert, Sebastian A. Kube, Simon Divilov, Asa Guest, Adam C. Zettel, David Hicks, Sean D. Griesemer, Nico Hotz, Xiomara Campilongo, Siya Zhu, Axel van de Walle, Jan Schroers, Stefano Curtarolo
Tailoring material properties often requires understanding the solidification process. Herein, we introduce the geometric descriptor Soliquidy, which numerically captures the Euclidean transport cost between the translationally disordered versus ordered states of a materials. As a testbed, we apply Soliquidy to the classification of glass-forming metal alloys. By extending and combining an experimental library of metallic thin-films (glass/no-glass) with the this http URL computational database (geometrical and energetic information of mixtures) we found that the combination of Soliquity and formation enthalpies generates an effective classifier for glass formation. Such classifier is then used to tackle a public dataset of metallic glasses showing that the glass-agnostic assumptions of Soliquity can be useful for understanding kinetically-controlled phase transitions.
Materials Science (cond-mat.mtrl-sci)
9 pages, 7 figures
Few-Mode and Anisotropic Quantum Transport in InSb Nanoribbons Using an All-van der Waals Material-Based Gate
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Colin J. Riggert, Pim Lueb, Tyler Littmann, Ghada Badawy, Marco Rossi, Paul A. Crowell, Erik P.A.M. Bakkers, Vlad S. Pribiag
High-quality electrostatic gating is a fundamental ingredient for successful semiconducting device physics, and a key element of realizing clean quantum transport. Inspired by the widespread improvement of transport quality when two-dimensional van der Waals (vdW) materials are gated exclusively by other vdW materials, we have developed a method for gating non-vdW materials with an all-vdW gate stack, consisting of a hexagonal boron nitride dielectric layer and a few-layer graphite gate electrode. We demonstrate this gating approach on MOVPE-grown InSb nanoribbons (NRs), a novel variant of the InSb nanowire, with a flattened cross-section. In our all-vdW gated NR devices we observe conductance features that are reproducible and have low- to near-zero gate hysteresis. We also report quantized conductance, which persists to lower magnetic fields and longer channel lengths than typical InSb nanowire devices reported to date. Additionally, we observe level splitting that is highly anisotropic in an applied magnetic field, which we attribute to the ribbon cross-section. The performance of our devices is consistent with the reduced disorder expected from the all-vdW gating scheme, and marks the first report of ballistic, few-modes quantum transport in a non-vdW material with an all-vdW gate. Our results establish all-vdW gating as a promising approach for high-quality gating of non-vdW materials for quantum transport, which is in principle applicable generically, beyond InSb systems. In addition, the work showcases the specific potential of all-vdW gate/InSb NR devices for enabling clean quantum devices that may be relevant for spintronics and topological superconductivity studies.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
25 pages, 4 figures, plus supplementary material
Learning Metal Microstructural Heterogeneity through Spatial Mapping of Diffraction Latent Space Features
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Mathieu Calvat, Chris Bean, Dhruv Anjaria, Hyoungryul Park, Haoren Wang, Kenneth Vecchio, J.C. Stinville
To leverage advancements in machine learning for metallic materials design and property prediction, it is crucial to develop a data-reduced representation of metal microstructures that surpasses the limitations of current physics-based discrete microstructure descriptors. This need is particularly relevant for metallic materials processed through additive manufacturing, which exhibit complex hierarchical microstructures that cannot be adequately described using the conventional metrics typically applied to wrought materials. Furthermore, capturing the spatial heterogeneity of microstructures at the different scales is necessary within such framework to accurately predict their properties. To address these challenges, we propose the physical spatial mapping of metal diffraction latent space features. This approach integrates (i) point diffraction data encoding via variational autoencoders or contrastive learning and (ii) the physical mapping of the encoded values. Together these steps offer a method offers a novel means to comprehensively describe metal microstructures. We demonstrate this approach on a wrought and additively manufactured alloy, showing that it effectively encodes microstructural information and enables direct identification of microstructural heterogeneity not directly possible by physics-based models. This data-reduced microstructure representation opens the application of machine learning models in accelerating metallic material design and accurately predicting their properties.
Materials Science (cond-mat.mtrl-sci), Artificial Intelligence (cs.AI)
Local Basis Transformation to Mitigate Negative Sign Problems
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-31 20:00 EST
Quantum Monte Carlo (QMC) methods for the frustrated quantum spin systems occasionally suffer from the negative sign problem, which makes simulations exponentially harder for larger systems at lower temperatures and severely limits QMC’s application across a wide range of spin systems. This problem is known to depend on the choice of representation basis. We propose a systematic approach for mitigating the sign problem independent of the given Hamiltonian or lattice structure. We first introduce the concept of negativity to characterize the severity of the negative sign problem. We then demonstrate the existence of a locally defined quantity, the L1 adaptive loss function, which effectively approximates negativity, especially in frustration-free systems. Using the proposed loss function, we demonstrate that optimizing the representation basis can mitigate the negative sign. This is evidenced by several frustration-free models and other important quantum spin systems. Furthermore, we compare the effectiveness of unitary transformations against the standard orthogonal transformation and reveal that unitary transformations can effectively mitigate the sign problem in certain cases.
Strongly Correlated Electrons (cond-mat.str-el), Statistical Mechanics (cond-mat.stat-mech)
13 pages, 13 figures. This paper proposes a systematic local basis transformation approach to mitigate the negative sign problem in Quantum Monte Carlo simulations. We introduce the concept of negativity and an L1 adaptive loss function to optimize basis representations
Polarization-Resolved Core Exciton Dynamics in LiF Using Attosecond Transient Absorption Spectroscopy
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Kylie J Gannan, Lauren B Drescher, Rafael Quintero-Bermudez, Navdeep Rana, Chengye Huang, Kenneth Schafer, Mette B Gaarde, Stephen R Leone
The ability to control absorption by modifying the polarization of light presents an exciting opportunity to experimentally determine the orbital alignment of absorption features. Here, attosecond extreme ultraviolet (XUV) transient absorption spectroscopy is used to investigate the polarization dependence of core exciton dynamics in LiF thin films at the Li+ K edge. XUV pulses excite electrons from the Li 1s core level into the conduction band, allowing for the formation of a p-orbital-like core exciton, aligned along the XUV light polarization axis. A sub-5 fs near-infrared (NIR) probe pulse then arrives at variable time delays, perturbing the XUV-excited states and allowing the coherence decay of the core exciton to be mapped. The coherence lifetimes are found to be ~2.4 +- 0.4 fs, which is attributed to a phonon-mediated dephasing mechanism as in previous core exciton studies. The differential absorption features are also shown to be sensitive to the relative polarization of the XUV and NIR fields. The parallel NIR probe induces couplings between the initial XUV-excited p-like bright exciton and s-like dark excitons. When crossed pump and probe polarizations are used, the coupling between the bright and dark states is no longer dipole-allowed, and the transient absorption signal associated with the coupling is suppressed by approximately 90%. This interpretation is supported by simulations of a few-level model system, as well as analysis of the calculated band structure. The results indicate that laser polarization can serve as a powerful experimental tool for exploring the orbital alignment of core excitonic states in solid-state materials.
Materials Science (cond-mat.mtrl-sci), Chemical Physics (physics.chem-ph), Optics (physics.optics)
18 pages, 14 figures
A Phase Diagram for Crystallization of a Complex Macromolecular Assembly
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-31 20:00 EST
Vivekananda Bal, Jacqueline M. Wolfrum, Paul W. Barone, Stacy L. Springs, Anthony J. Sinskey, Robert M. Kotin, Richard D. Braatz
Crystallization of biological molecules has high potential to solve some challenges in drug manufacturing. Thus, understanding the process is critical to efficiently adapting crystallization to biopharmaceutical manufacturing. This article describes phase behavior for the solution crystallization of recombinant adeno-associated virus (rAAV) capsids of serotypes 5, 8, and 9 as model biological macromolecular assemblies. Hanging-drop vapor diffusion experiments are used to determine the combined effects of pH and polyethylene glycol (PEG) and sodium chloride concentrations in which full and empty capsids nucleate and grow. Full and empty capsids show different crystallization behavior although they possess similar capsid structure and similar outer morphology with icosahedral symmetry and 2-fold, 3-fold, and 5-fold symmetry. The differential charge environment surrounding full and empty capsids is found to influence capsid crystallization. The crystal growth rate is found to be affected by the mass of the macromolecular assembly rather than the structure/shape of the macromolecular assembly. The regions of precipitant concentrations and pH in which crystallization occurs are found to be different for different rAAV serotypes and for full and empty capsids for each serotype. Depending on the precipitant concentrations and the rAAV serotype, a variety of complex crystal morphologies are formed and a variety of non-crystallization outcomes such as unidentified dense solid-phase/opaque crystals and an oil/dense phase is observed. The well-defined dense phase/oil is found to be converted into a solid phase over a long period of time. Trends in the crystallization of full and empty capsids between serotypes is observed to be altered by the extent of post-translational modifications (PTMS) associated with the massive macromolecular proteinaceous assembly.
Soft Condensed Matter (cond-mat.soft), Applied Physics (physics.app-ph)
22 pages, 9 figures
Dynamics with Simultaneous Dissipations to Fermionic and Bosonic Reservoirs
New Submission | Other Condensed Matter (cond-mat.other) | 2025-01-31 20:00 EST
Elvis F. Arguelles, Osamu Sugino
We introduce a non-phenomenological framework based on the influence functional method to incorporate simultaneous interactions of particles with fermionic and bosonic thermal reservoirs. In the slow-motion limit, the electronic friction kernel becomes Markovian, enabling an analytical expression for the friction coefficient. The framework is applied to a prototypical electrochemical system, where the metal electrode and solvent act as fermionic and bosonic reservoirs, respectively. We investigate quantum vibrational relaxation of hydrogen on metal surfaces, showing that dissipation to electron-hole pairs reduces the relaxation time. Additionally, in solvated proton discharge, electronic friction prolongs charge transfer by delaying proton transitions between potential wells. This study provides new insights into the interplay of solvent and electronic dissipation effects, with direct relevance to electrochemical processes and other systems involving multiple thermal reservoirs.
Other Condensed Matter (cond-mat.other), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Statistical Mechanics (cond-mat.stat-mech)
A tomographic interpretation of structure-property relations for materials discovery
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Raul Ortega-Ochoa, Alán Aspuru-Guzik, Tejs Vegge, Tonio Buonassisi
Recent advancements in machine learning (ML) for materials have demonstrated that “simple” materials representations (e.g., the chemical formula alone without structural information) can sometimes achieve competitive property prediction performance in common-tasks. Our physics-based intuition would suggest that such representations are “incomplete”, which indicates a gap in our understanding. This work proposes a tomographic interpretation of structure-property relations of materials to bridge that gap by defining what is a material representation, material properties, the material and the relationships between these three concepts using ideas from information theory. We verify this framework performing an exhaustive comparison of property-augmented representations on a range of material’s property prediction objectives, providing insight into how different properties can encode complementary information.
Materials Science (cond-mat.mtrl-sci), Computational Physics (physics.comp-ph)
Competition between excitonic insulators and quantum Hall states in correlated electron-hole bilayers
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Ruishi Qi, Qize Li, Zuocheng Zhang, Zhiyuan Cui, Bo Zou, Haleem Kim, Collin Sanborn, Sudi Chen, Jingxu Xie, Takashi Taniguchi, Kenji Watanabe, Michael F. Crommie, Allan H. MacDonald, Feng Wang
Excitonic insulators represent a unique quantum phase of matter, providing a rich ground for studying exotic quantum bosonic states. Strongly coupled electron-hole bilayers, which host stable dipolar exciton fluids with an exciton density that can be adjusted electrostatically, offer an ideal platform to investigate correlated excitonic insulators. Based on electron-hole bilayers made of MoSe2/hBN/WSe2 heterostructures, here we study the behavior of excitonic insulators in a perpendicular magnetic field. We report the observation of excitonic quantum oscillations in both Coulomb drag signals and electrical resistance at low to medium magnetic fields. Under a strong magnetic field, we identify multiple quantum phase transitions between the excitonic insulator phase and the bilayer quantum Hall insulator phase. These findings underscore the interplay between the electron-hole interactions and Landau level quantization that opens new possibilities for exploring quantum phenomena in composite bosonic insulators.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Strongly Correlated Electrons (cond-mat.str-el)
Charge state tuning of spin defects in hexagonal boron nitride
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Jules Fraunié, Tristan Clua-Provost, Sébastien Roux, Zhao Mu, Adrien Delpoux, Grégory Seine, Delphine Lagarde, Kenji Watanabe, Takashi Taniguchi, Xavier Marie, Thomas Poirier, James H. Edgar, Jeremie Grisolia, Benjamin Lassagne, Alain Claverie, Vincent Jacques, Cedric Robert
Boron vacancies in hexagonal boron nitride (hBN) are among the most extensively studied optically active spin defects in van der Waals crystals, due to their promising potential to develop two-dimensional (2D) quantum sensors. In this letter, we demonstrate the tunability of the charge state of boron vacancies in ultrathin hBN layers, revealing a transition from the optically active singly negatively charged state to the optically inactive doubly negatively charged state when sandwiched between graphene electrodes. Notably, there is a photoluminescence quenching of a few percent upon the application of a bias voltage between the electrodes. Our findings emphasize the critical importance of considering the charge state of optically active defects in 2D materials, while also showing that the negatively charged boron vacancy remains robust against external perpendicular electric fields. This stability makes it a promising candidate for integration into various van der Waals heterostructures.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Quantum Physics (quant-ph)
Exciton-polariton condensate in the van der Waals magnet CrSBr
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Bo Han, Hangyong Shan, Kok Wee Song, Lukas Lackner, Martin Esmann, Vita Solovyeva, Falk Eilenberger, Jakub Regner, Zdeněk Sofer, Oleksandr Kyriienko, Christian Schneider
Van der Waals magnets are an emergent material class of paramount interest for fundamental studies in coupling light with matter excitations, which are uniquely linked to their underlying magnetic properties. Among these materials, the magnetic semiconductor CrSBr is possibly a first playground where we can study simultaneously the interaction of photons, magnons, and excitons at the quantum level. Here we demonstrate a coherent macroscopic quantum phase, the bosonic condensation of exciton-polaritons, which emerges in a CrSBr flake embedded in a fully tunable cryogenic open optical cavity. The Bose condensate is characterized by a highly non-linear threshold-like behavior, and coherence manifests distinctly via its first and second order quantum coherence. We find that the condensate’s non-linearity is highly susceptible to the magnetic order in CrSBr, and encounters a sign change depending on the antiferro- and ferromagnetic ordering. Our findings open a route towards magnetically controllable quantum fluids of light, and optomagnonic devices where spin magnetism is coupled to on-chip Bose-Einstein condensates.
Materials Science (cond-mat.mtrl-sci), Quantum Gases (cond-mat.quant-gas)
35 pages, 12 figures
Unveiling Topological Hinge States in the Higher-Order Topological Insulator WTe$_2$ Based on the Fractional Josephson Effect
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Yong-Bin Choi, Jinho Park, Woochan Jung, Sein Park, Mazhar N. Ali, Gil-Ho Lee
Higher-order topological insulators (HOTIs) represent a novel class of topological materials, characterised by the emergence of topological boundary modes at dimensions two or more lower than those of bulk materials. Recent experimental studies have identified conducting channels at the hinges of HOTIs, although their topological nature remains unexplored. In this study, we investigated Shapiro steps in Al-WTe$_2$-Al proximity Josephson junctions (JJs) under microwave irradiation and examined the topological properties of the hinge states in WTe$_2$. Specifically, we analysed the microwave frequency dependence of the absence of the first Shapiro step in hinge-dominated JJs, attributing this phenomenon to the 4$\pi$-periodic current-phase relationship characteristic of topological JJs. These findings may encourage further research into topological superconductivity with topological hinge states in superconducting hybrid devices based on HOTIs. Such advances could lead to the realisation of Majorana zero modes for topological quantum physics and pave the way for applications in spintronic devices.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci), Superconductivity (cond-mat.supr-con)
Refining interface stress measurement in nanomultilayers through layer corrugation and interface roughness corrections
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Yang Hu, Aleksandr Druzhinin, Claudia Cancellieri, Vladyslav Turlo
We introduce new models that incorporate layer corrugation and interface roughness into standard approaches for measuring interface stress in nanomultilayers (NMLs). Applied to Cu/W NMLs, these models show that ignoring such features can inflate measured interface stress by up to 0.4 J/m^2. However, corrugation and roughness alone cannot account for the extreme stresses reported, suggesting that atomic-scale phenomena (e.g., intermixing and metastable phase formation at the interfaces) dominate. These findings highlight the importance of balancing bilayer counts and thickness-to-roughness ratios for reliable stress quantification, providing a practical pathway to designing and characterizing advanced nanocomposite coatings with improved accuracy.
Materials Science (cond-mat.mtrl-sci), Computational Physics (physics.comp-ph)
Interlayer phase coherence and composite fermions
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
The fractional quantum Hall effect (FQHE) realized in two-dimensional electron systems is explained by the emergent composite fermions (CF) out of ordinary electrons. It is possible to write down explicit wavefunctions explaining many if not all FQHE states. In bilayer systems there is a regime at integer filling of the lowest Landau level that displays a spontaneous breakdown of the U(1) relative phase between the two layers. This can be seen as interlayer phase coherence (ILC) in terms of electrons. Recent experiments in double layer samples of graphene have revealed the appearance of many FQHE states unique to the bilayer case. We discuss extensions of the CF idea in this situation as well as the possible existence of ILC of CFs.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Strongly Correlated Electrons (cond-mat.str-el)
10 pages, talk given at the workshop “open questions in the quantum many-body problem” held in Institut Henri Poincare in Paris, July 2024, organized by Y. Castin and C. Sa de Melo. More beautiful version with fancy owl logo available at the journal website (open access)
Comptes Rendus. Physique, Volume 26 (2025), pp. 113-124
Large frequency nonreciprocity of azimuthal spin wave modes in submicron vortex state disks
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Sali Salama, Joo-Von Kim, Abdelmadjid Anane, Jean-Paul Adam
Vortex states in thin film disks host spin wave modes that are geometrically quantized according to their radial and azimuthal indices. Previous studies have shown that hybridization between these modes and the vortex core results in a sizeable frequency nonreciprocity between low-order clockwise and counterclockwise propagating azimuthal modes. Here, we present a computational study of these spin wave modes in submicron disks in which the spatial extension of the vortex core becomes comparable to the wavelength of certain modes. In such cases, we find that the frequency nonreciprocity can be large even for higher order radial and azimuthal indices, reaching several GHz and comparable to the mode frequencies themselves.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Tensor network state methods and quantum information theory for strongly correlated molecular systems
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-31 20:00 EST
Miklós Antal Werner, Andor Menczer, Örs Legeza
A brief pedagogical overview of recent advances in tensor network state methods are presented that have the potential to broaden their scope of application radically for strongly correlated molecular systems. These include global fermionic mode optimization, i.e., a general approach to find an optimal matrix product state (MPS) parametrization of a quantum many-body wave function with the minimum number of parameters for a given error margin, the restricted active space DMRG-RAS-X method, multi-orbital correlations and entanglement, developments on hybrid CPU-multiGPU parallelization, and an efficient treatment of non-Abelian symmetries on high-performance computing (HPC) infrastructures. Scaling analysis on NVIDIA DGX-A100 platform is also presented.
Strongly Correlated Electrons (cond-mat.str-el), Chemical Physics (physics.chem-ph), Computational Physics (physics.comp-ph)
17 pages, 21 figures
Curvature-sensing and generation of membrane proteins: a review
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-31 20:00 EST
Membrane proteins are crucial in regulating biomembrane shapes and controlling the dynamic changes in membrane morphology during essential cellular processes. These proteins can localize to regions with their preferred curvatures (curvature sensing) and induce localized membrane curvature. Thus, this review describes the recent theoretical development in membrane remodeling performed by membrane proteins. The mean-field theories of protein binding and the resulting membrane deformations are reviewed. The effects of hydrophobic insertions on the area-difference elasticity energy and that of intrinsically disordered protein domains on the membrane bending energy are discussed. For the crescent-shaped proteins, such as Bin/Amphiphysin/Rvs superfamily proteins, anisotropic protein bending energy and orientation-dependent excluded volume significantly contribute to curvature sensing and generation. Moreover, simulation studies of membrane deformations caused by protein binding and colloidal particle adhesion are reviewed, including domain formation, budding, and tubulation.
Soft Condensed Matter (cond-mat.soft), Biological Physics (physics.bio-ph)
19 pages, 13 figures
Ultra-large mutually synchronized networks of 10 nm spin Hall nano-oscillators
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Nilamani Behera, Avinash Kumar Chaurasiya, Akash Kumar, Roman Khymyn, Artem Litvinenko, Lakhan Bainsla, Ahmad A. Awad, Johan Åkerman
While mutually interacting spin Hall nano-oscillators (SHNOs) hold great promise for wireless communication, neural networks, neuromorphic computing, and Ising machines, the highest number of synchronized SHNOs remains limited to $N$ = 64. Using ultra-narrow 10 and 20-nm nano-constrictions in W-Ta/CoFeB/MgO trilayers, we demonstrate mutually synchronized SHNO networks of up to $N$ = 105,000. The microwave power and quality factor scale as $N$ with new record values of 9 nW and $1.04 \times 10^6$, respectively. An unexpectedly strong array size dependence of the frequency-current tunability is explained by magnon exchange between nano-constrictions and magnon losses at the array edges, further corroborated by micromagnetic simulations and Brillouin light scattering microscopy. Our results represent a significant step towards viable SHNO network applications in wireless communication and unconventional computing.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Applied Physics (physics.app-ph)
15 pages
Disentangling real space fluctuations: the diagnostics of metal-insulator transitions beyond single-particle spectral functions
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-31 20:00 EST
Michael Meixner, Marcel Krämer, Nils Wentzell, Pietro M. Bonetti, Sabine Andergassen, Alessandro Toschi, Thomas Schäfer
The destruction of metallicity due to the mutual Coulomb interaction of quasiparticles gives rise to fascinating phenomena of solid state physics such as the Mott metal-insulator transition and the pseudogap. A key observable characterizing their occurrences is the single-particle spectral function, determined by the fermionic self-energy. In this paper we investigate in detail how real space fluctuations are responsible for a self-energy that drives the Mott-Hubbard metal-insulator transition. To this aim we first introduce a real space fluctuation diagnostics approach to the Hedin equation, which connects the fermion-boson coupling vertex $\lambda$ to the self-energy $\Sigma$. Second, by using cellular dynamical mean-field theory calculations for $\lambda$ we identify the leading physical processes responsible for the destruction of metallicity across the transition.
Strongly Correlated Electrons (cond-mat.str-el)
21 pages, 17 figures
Active rheology of soft solids performed with acoustical tweezers
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-31 20:00 EST
Antoine Penneron, Thomas Brunet, Diego Baresch
Single-beam acoustical tweezers are used to manipulate individual microbubbles and provide quantitative measurements of the local shear modulus of soft hydrogels. The microbubbles are directly generated by electrolysis of the hydrogel and their displacement is detected using optical microscopy in the focal plane of a focused vortex beam. Microbubbles displaced off-axis can be pulled by a restoring radial force component that forms a stable two-dimensional trap. We also observe an off-axis tangential microbubble motion that is due to the transfer of the beam’s angular momentum flux. A simple elastic model for the hydrogel deformation combined with radiation force calculations finally provide local values of the medium’s shear modulus, which are found to be in good agreement with standard bulk measurements performed with a rheometer. Our results suggest that acoustical tweezers are relevant tools to characterize the local mechanical properties of complex soft materials opening new opportunities in the field of active rheology.
Soft Condensed Matter (cond-mat.soft), Classical Physics (physics.class-ph)
Simulation of the crystallization kinetics of Ge$_2$Sb$_2$Te$_5$ nanoconfined in superlattice geometries for phase change memories
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Debdipto Acharya, Omar Abou El Kheir, Simone Marcorini, Marco Bernasconi
Phase change materials are the most promising candidates for the realization of artificial synapsis for neuromorphic computing. Different resistance levels corresponding to analogic values of the synapsis conductance can be achieved by modulating the size of an amorphous region embedded in its crystalline matrix. Recently, it has been proposed that a superlattice made of alternating layers of the phase change compound Sb$_2$Te$_3$ and of the TiTe$_2$ confining material allows for a better control of multiple intermediate resistance states and for a lower drift with time of the electrical resistance of the amorphous phase. In this work, we consider to substitute Sb$_2$Te$_3$ with the Ge$_2$Sb$_2$Te$_5$ prototypical phase change compound that should feature better data retention. By exploiting molecular dynamics simulations with a machine learning interatomic potential, we have investigated the crystallization kinetics of Ge$_2$Sb$_2$Te$_5$ nanoconfined in geometries mimicking Ge$_2$Sb$_2$Te$_5$/TiTe$_2$ superlattices. It turns out that nanoconfinement induces a slight reduction in the crystal growth velocities with respect to the bulk, but also an enhancement of the nucleation rate due to heterogeneous nucleation. The results support the idea of investigating Ge$_2$Sb$_2$Te$_5$/TiTe$_2$ superlattices for applications in neuromorphic devices with improved data retention. The effect on the crystallization kinetics of the addition of van der Waals interaction to the interatomic potential is also discussed.
Materials Science (cond-mat.mtrl-sci)
Implications of the multi-minima character of molecular crystal phases onto the free energy
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Marco Krummenacher, Martin Sommer-Jörgensen, Moritz Gubler, Jonas A. Finkler, Ehsan Rahmatizad Khajehpasha, Giuseppe Fisicaro, Stefan Goedecker
In recent years, significant advancements in computational methods have dramatically enhanced the precision in determining the energetic ranking of different phases of molecular crystals. The developments mainly focused on providing accurate dispersion corrected exchange correlation functionals and methods for describing the vibrational entropy contributions to the free energy at finite temperatures. Several molecular crystals phases were recently found to have of multi-minima character. For our investigations we highlight the multi-minima character in the example of the molecular crystal consisting of N-(4-Methylbenzylidene)-4-methylalanine. We explore its potential energy landscape on the full DFT level or with a machine learned potential that was fitted to DFT data. We calculate not only many local minima but also exact barriers along transformation pathways to demonstrate the multi-minima character of our system. Furthermore, we present a framework, based on the quantum superposition method, that includes both configurational and vibrational entropy. As an example, we show for our system that the transition temperature between two of its phases is afflicted by an error of about 200 K if the multi-minima character is not taken into account. This indicates that it is absolutely essential to consider configurational entropy to obtain reliable finite temperature free energy rankings for complex molecular crystals.
Materials Science (cond-mat.mtrl-sci), Computational Physics (physics.comp-ph)
An extensive thermal conductivity measurement method based on atomic force microscopy
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
T. Serkan Kasırga, Berke Köker
Heat transport in low-dimensional solids can significantly differ from their bulk counterpart due to various size-related effects. This offers rich heat transport phenomena to emerge. However, finding an appropriate thermometry method for thermal conductivity measurements at the reduced size and dimensionality of the samples is a challenge. Here, we propose and study the feasibility of a nanoscale resolution thermal conductivity measurement method based on bolometric thermometry implemented on an atomic force microscopy (AFM). The local heat exchange between the AFM tip and the sample occurs at a suspended section of the sample, and thermal modeling of the measured electrical resistance change resulting from the bolometric effect provides a unique value for thermal conductivity. As we illustrate via thermal simulations, the proposed method can measure thermal conductivity with thermal disturbance to the sample in as little as 0.2 K at ~20 nm lateral resolution. Our in-depth analysis shows the feasibility and extensive applicability of the proposed AFM-based bolometric thermometry method on low-dimensional materials both in diffusive and ballistic heat transport regimes from cryogenic to above-room temperature. Consequently, the proposed method can lead to a deeper experimental understanding of fundamental questions in nanoscale and low-dimensional heat transport phenomena in many different material classes, as well as Fourier and non-Fourier heat transfer regimes.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Interplay of $d$- and $p$-States in RbTi$_3$Bi$_5$ and CsTi$_3$Bi$_5$ Flat-Band Kagome Metals
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-31 20:00 EST
M. Wenzel, E. Uykur, A. A. Tsirlin, A. N Capa Salinas, B. R. Ortiz, S. D. Wilson, M. Dressel
Shifting the Fermi level of the celebrated $AM_3X_5$ (135) compounds into proximity of flat bands strongly enhances electronic correlations and severely affects the formation of density waves and superconductivity. Our broadband infrared spectroscopy measurements of RbTi$_3$Bi$_5$ and CsTi$_3$Bi$_5$ combined with density-functional band-structure calculations reveal that the correlated Ti $d$-states are intricately coupled with the Bi $p$-states that form a tilted Dirac crossing. Electron-phonon coupling manifests itself in the strong damping of itinerant carriers and in the anomalous shape of the phonon line in RbTi$_3$Bi$_5$. An anomaly in these spectral features around 150 K can be paralleled to the onset of nematicity detected by low-temperature probes. Our findings show that the materials with low band filling open unexplored directions in the physics of kagome metals and involve electronic states of different nature strongly coupled with lattice dynamics.
Strongly Correlated Electrons (cond-mat.str-el)
Rigorous Test for Quantum Integrability and Nonintegrability
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-01-31 20:00 EST
Whether or not a quantum many-body system is integrable, which is characterized by the presence or absence of local conserved quantities, drastically impacts the dynamics of isolated systems, including thermalization. Nevertheless, a rigorous and comprehensive method for deciding integrability or nonintegrability has remained elusive. In this paper, we address this challenge by introducing rigorously provable tests for integrability and nonintegrability of quantum spin systems with finite-range interactions. Our approach establishes a new paradigm, moving beyond the conventional artisanal methods in the study of nonintegrability. Furthermore, it partially resolves the long-standing conjecture that integrability is governed by the presence or absence of local conserved quantities with small supports. The proposed framework guarantees that the nonintegrability of one-dimensional spin systems with translational symmetry can be confirmed algorithmically, regardless of system size.
Statistical Mechanics (cond-mat.stat-mech), Mathematical Physics (math-ph), Quantum Physics (quant-ph)
9+4 pages
Elastic constants of single-crystalline NiTi studied by resonant ultrasound spectroscopy
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Lucie Bodnárová (1), Michaela Janovská (1), Martin Ševčík (1), Miroslav Frost (1), Lukáš Kadeřávek (2), Jaromír Kopeček (2), Hanuš Seiner (1), Petr Sedlák (1)- ((1) Institute of Thermomechanics, Czech Acad Sci, Prague, Czechia, (2) Institute of Physics, Czech Acad Sci, Prague, Czechia)
Contactless, laser-based resonant ultrasound spectroscopy was utilized to monitor changes in elastic properties in single-crystalline NiTi shape memory alloy. It was observed that the elastic behavior of the temperature-induced B19$^\prime$ martensite adopts the symmetry elements of the parent austenite phase, and thus, the changes over the transformation temperature can be represented by the temperature evolution of three cubic elastic coefficients. The experiments confirm that the transition during the cooling run is preceded by pronounced softening of the $c_{44}$ elastic coefficient, which leads to nearly complete vanishing of elastic anisotropy prior to the transition. Below the transition, this coefficient remains soft, and the character of anisotropy switches from $c_{44}/c^\prime>1$ to $c_{44}/c^\prime<1$. We rationalize this behavior from the mechanical instability of the B19$^\prime$ lattice with respect to shears along the (001)$_{B19^\prime}$ plane, which is known from first-principles calculations.
Materials Science (cond-mat.mtrl-sci)
Manuscript submitted to Shape Memory and Superelasticity
Optimal performance of thermoelectric devices with small external irreversibility
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-01-31 20:00 EST
Rajeshree Chakraborty, Ramandeep S. Johal
In the thermodynamic analysis of thermoelectric devices, typical irreversibilities are for the processes of finite-rate heat transfer and Joule heating. Approximate analyses often focus on either internal or external irreversibility, yielding well-known expressions for the efficiency at maximum power (EMP), such as the Curzon-Ahlborn value for endoreversible model and the Schmiedl-Seifert form for exoreversible model. Within the Constant Properties model, we formulate a scenario that incorporates internal as well as external irreversibilities simultaneously. We employ the approximation of a symmetric and small external irreversibility (SEI), confining to the regime where the external conductance of the heat exchangers is large in comparison to the internal thermal conductance of the thermoelectric material. This approach allows us to derive a general expression for EMP, which depends on the ratio of internal to external conductance, apart from the figure of merit and ratio of temperatures. Extending our study to thermoelectric refrigerators under the similar assumptions, we also analyze the efficiency at maximum cooling power.
Statistical Mechanics (cond-mat.stat-mech)
14 pages, 5 figures
Pathways to Bubble and Skyrmion Lattice Formation in Fe/Gd Multilayers
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Tim Titze (1), Sabri Koraltan (2 and 3), Mailin Matthies (1), Timo Schmidt (4), Dieter Suess (3), Manfred Albrecht (4), Stefan Mathias (1), Daniel Steil (1) ((1) Universität Göttingen, Germany, (2) Technische Universität Wien, Austria, (3) Universitity of Vienna, Austria, (4) University of Augsburg, Germany)
The creation and control of magnetic spin textures is of great interest in fundamental research and future device-oriented applications. Fe/Gd multilayers host a rich variety of magnetic textures including topologically trivial bubbles and topologically protected skyrmions. Using time-resolved Kerr spectroscopy, we highlight how various control strategies, including temperature, out-of-plane magnetic fields and femtosecond light excitation, can be used to create such textures via different pathways. We find that varying the magnetic field for constant temperature leads to a different ($H, T$)-phase diagram of magnetic textures than moving along a temperature trajectory for constant magnetic field. Micromagnetic simulations corroborate this finding and allow to visualize the different paths taken. Furthermore, we show that the creation of bubbles and skyrmions in this material via impulsive light excitation is not solely governed by temperature-driven processes, since bubbles and skyrmions can be stabilized in parts of the ($H, T$)-phase diagram, where neither the constant temperature nor the constant magnetic field trajectory predict their existence. Using this phase diagram, we reason why bubble and skyrmion creation in this particular system is only possible from the stripe domain state. Our observations provide a versatile toolkit for tailoring the creation of magnetic spin textures in Fe/Gd multilayers.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci)
10 pages, 9 figures
Dissipation bounds the coherence of stochastic limit cycles
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-01-31 20:00 EST
Davide Santolin, Gianmaria Falasco
Overdamped stochastic systems maintained far from equilibrium can display sustained oscillations with fluctuations that decrease with the system size. The correlation time of such noisy limit cycles expressed in units of the cycle period is upper-bounded by the entropy produced per oscillation. We prove this constraint for first-order nonlinear systems in arbitrary dimensions perturbed by weak, uncorrelated Gaussian noise. We then extend the result to important examples of more general stochastic dynamics, including electronic and chemical clocks, illustrating the practical relevance of the dissipation-coherence bound for electronic computing and thermodynamic inference.
Statistical Mechanics (cond-mat.stat-mech)
Quantifying the generation of negatively charged boron vacancies in He-ion irradiated hexagonal boron nitride
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Amedeo Carbone, Ilia D. Breev, Johannes Figueiredo, Silvan Kretschmer, Leonard Geilen, Amine Ben Mhenni, Johannes Arceri, Arkady V. Krasheninnikov, Martijn Wubs, Alexander W. Holleitner, Alexander Huck, Christoph Kastl, Nicolas Stenger
Hexagonal boron nitride (hBN) hosts luminescent defects possessing spin qualities compatible with quantum sensing protocols at room temperature. Vacancies, in particular, are readily obtained via exposure to high-energy ion beams. While the defect creation mechanism via such irradiation is well understood, the occurrence rate of optically active negatively charged vacancies ($V_B^-$) is an open question. In this work, we exploit focused helium ions to systematically generate optically active vacancy defects in hBN flakes at varying density. By comparing the density-dependent spin splitting measured by magnetic resonance to calculations based on a microscopic charge model, in which we introduce a correction term due to a constant background charge, we are able to quantify the number of $V_B^-$ defects generated by the ion irradiation. We find that only a small fraction (0.2%) of all vacancies is in the optically active, negatively charged state. Our results provide a protocol for measuring the generation efficiency of $V_B^-$, which is necessary for understanding and optimizing luminescent centers in hBN.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Main manuscript: 7 pages, 4 figures; Supplemental material: 6 pages, 7 figures
Nonequilibrium friction and free energy estimates for kinetic coarse-graining – Driven particles in responsive media
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-01-31 20:00 EST
Sebastian Milster, Joachim Dzubiella, Gerhard Stock, Steffen Wolf
Predicting the molecular friction and energy landscapes under nonequilibrium conditions is key to coarse-graining the dynamics of selective solute transport through complex, fluctuating and responsive media, e.g., polymeric materials such as hydrogels, cellular membranes or ion channels. The analysis of equilibrium ensembles already allows such a coarse-graining for very mild nonequilibrium conditions. Yet in the presence of stronger external driving and/or inhomogeneous setups, the transport process is governed apart from a potential of mean force also by a nontrivial position- and velocity-dependent friction. It is therefore important to find suitable and efficient methods to estimate the mean force and the friction landscape, which then can be used in a low-dimensional, coarse-grained Langevin framework to predict the system’s transport properties and timescales. In this work, we evaluate different coarse-graining approaches based on constant-velocity constraint simulations for generating such estimates using two model systems, which are a 1D responsive barrier as a minimalistic model and a single tracer driven through a 3D bead-spring polymer membrane as a more sophisticated problem. Finally, we demonstrate that the estimates from 3D constant-velocity simulations yield the correct velocity-dependent friction, which can be directly utilized for coarse-grained (1D) Langevin simulations with constant external driving forces.
Soft Condensed Matter (cond-mat.soft), Statistical Mechanics (cond-mat.stat-mech), Applied Physics (physics.app-ph), Computational Physics (physics.comp-ph)
Seven Figures. This preprint is the unedited version of a manuscript that has been sent to a scientific publisher for consideration as an article in a peer-reviewed journal. Copyright with the authors and the publisher after publication
Magnetism and hidden quantum geometry in charge neutral twisted trilayer graphene
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Alina Wania Rodrigues, Maciej Bieniek, Daniel Miravet, Pawel Hawrylak
Here we present a theory of mirror-symmetric magic angle twisted trilayer graphene. The electronic properties are described by a Hubbard model with long range tunneling matrix elements. The electronic properties are obtained by solving the mean field Hubbard model. We obtain the bandstructure with characteristic flat bands and a Dirac cone. At charge neutrality, turning on electron-electron interactions results in metallic to antiferomagnetic phase transition, for Hubbard interaction strength considerably smaller than in other graphene multilayers. We analyze the stability of the antiferromagnetic state against the symmetry breaking induced by hexagonal boron nitride encapsulation, and mirror symmetry breaking caused by the application of electric fields that mix the Dirac cone with the flat bands. Additionally, we explore the topological properties of the system, revealing a hidden quantum geometry. Despite the flat bands having zero Chern numbers, the multiband Berry curvature distribution over the moiré Brillouin zone exhibits a non-trivial structure. Finally, we propose a mechanism to tune this quantum geometry, providing a pathway to control the system’s topological properties.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Strongly Correlated Electrons (cond-mat.str-el)
Deep learning with reflection high-energy electron diffraction images to predict cation ratio in Sr$x$Ti${1-x}$O3 thin films
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-01-31 20:00 EST
Sumner B. Harris, Patrick T. Gemperline, Christopher M. Rouleau, Rama K. Vasudevan, Ryan B. Comes
Machine learning (ML) with in situ diagnostics offers a transformative approach to accelerate, understand, and control thin film synthesis by uncovering relationships between synthesis conditions and material properties. In this study, we demonstrate the application of deep learning to predict the stoichiometry of Sr$x$Ti${1-x}$O3 thin films using reflection high-energy electron diffraction images acquired during pulsed laser deposition. A gated convolutional neural network trained for regression of the Sr atomic fraction achieved accurate predictions with a small dataset of 31 samples. Explainable AI techniques revealed a previously unknown correlation between diffraction streak features and cation stoichiometry in Sr$x$Ti${1-x}$O3 thin films. Our results demonstrate how ML can be used to transform a ubiquitous in situ diagnostic tool, that is usually limited to qualitative assessments, into a quantitative surrogate measurement of continuously valued thin film properties. Such methods are critically needed to enable real-time control, autonomous workflows, and accelerate traditional synthesis approaches.
Materials Science (cond-mat.mtrl-sci)
Transverse spin photocurrents in ultrathin topological insulator films
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-01-31 20:00 EST
Shahrzad Movafagh, Predrag Nikolic
Nonlinear helicity-dependent photocurrents have been reported in 3D topological materials lacking inversion symmetry. Here, we theoretically study the charge and spin photocurrents generated by linear and circularly polarized radiation in ultrathin topological insulator films. Using time-dependent perturbation theory and detailed balance equations, we find that helical transverse spin currents are generated when the symmetry between the top and bottom film surfaces is disturbed. Such spin currents are invariant under in-plane mirror transformations but have $s$-wave and $d$-wave components in regard to transformations under $\pi/2$ rotations. Spin current photo-transistors and amplifiers can be based on these effects.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Other Condensed Matter (cond-mat.other)
Derivation of the free energy, entropy and specific heat for planar Ising models: Application to Archimedean lattices and their duals
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-01-31 20:00 EST
Laurent Pierre, Bernard Bernu, Laura Messio
The 2d ferromagnetic Ising model was solved by Onsager on the square lattice in 1944, and an explicit expression of the free energy density $f$ is presently available for some other planar lattices. An exact derivation of the critical temperature $T_c$ only requires a partial derivation of $f$ and has been performed on many lattices, including the 11 Archimedean lattices. We give general expressions of the free energy, energy, entropy and specific heat for planar lattices with a single type of non-crossing links. The specific heat exhibits a logarithmic singularity at $T_c$: $c_V(T)\sim -A\ln|1-T_c/T|$, in all the ferromagnetic and some antiferromagnetic cases. While the non-universal weight $A$ of the leading term has often been evaluated, this is not the case for the sub-leading order term $B$ such that $c_V(T)+A\ln|1-T_c/T|\sim B$, despite its strong impact on $c_V(T)$ values in the vicinity of $T_c$, particularly important in experimental measurements. Explicit values of these thermodynamic quantities and of $A$ and $B$ are given for the Archimedean lattices and their dual for both ferromagnetic and antiferromagnetic interactions.
Statistical Mechanics (cond-mat.stat-mech)
22 pages, 48 with the appendices, 10 figures, 5 tables
Non-Hermitian catalysis of density-wave orders on Euclidean and hyperbolic lattices
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-01-31 20:00 EST
Christopher A. Leong, Bitan Roy
Depending on the lattice geometry, the nearest-neighbor (NN) tight-binding model for free fermions gives rise to particle-hole symmetric emergent Dirac liquid, Fermi liquid, and flat bands near the half-filling or zero-energy on bipartite Euclidean and hyperbolic lattices, respectively embedded on the flat and negatively curved spaces. Such noninteracting electronic fluids are characterized by a vanishing, a finite, and a diverging density of states near half-filling, respectively. A non-Hermitian generalization of this scenario resulting from an imbalance of the hopping amplitudes in the opposite directions between any pair of NN sites continues to accommodate a real eigenvalue spectrum over an extended non-Hermitian parameter regime. Most importantly, it reduces the band width without altering the characteristic scaling of the density of states close to the zero-energy. Here, we show that on two-dimensional bipartite Euclidean and hyperbolic lattices such a non-Hermiticity catalyzes the formation of both charge-density-wave and spin-density-wave orders at weaker (in comparison to the counterparts in conventional or Hermitian systems) NN Coulomb and on-site Hubbard repulsions, respectively. These two ordered states correspond to staggered patterns of average electronic density and spin between the NN sites, respectively, and both cause insulation in half-filled systems. We arrive at these conclusions by combining biorthogonal quantum mechanics and lattice-based self-consistent numerical mean-field analysis in the Hartree channel. We discuss the scaling of the associated mass gaps near the zero-energy with the non-Hermitian parameter, and also address the finite size scaling of the order parameters specifically on hyperbolic lattices with open boundary conditions. A robust general mathematical criterion for the proposed non-Hermitian catalysis mechanism for ordered phases is showcased.
Strongly Correlated Electrons (cond-mat.str-el), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Superconductivity (cond-mat.supr-con), High Energy Physics - Theory (hep-th)
25 Pages, 17 Figures, and 4 Tables (For full Abstract see manuscript)