CMP Journal 2025-05-17
Statistics
Physical Review Letters: 13
Physical Review X: 2
arXiv: 67
Physical Review Letters
Self-Testing Composite Measurements and Bound Entangled State in a Single Quantum Network
Research article | Quantum correlations in quantum information | 2025-05-16 06:00 EDT
Shubhayan Sarkar, Chandan Datta, Saronath Halder, and Remigiusz Augusiak
Within the quantum networks scenario we introduce a single scheme allowing one to certify three different types of composite projective measurements acting on a three-qubit Hilbert space: one constructed from genuinely entangled GHZ-like states, one constructed from fully product vectors that exhibit the phenomenon of nonlocality without entanglement, and a hybrid measurement obtained from an unextendible product basis. Noticeably, we certify a basis exhibiting nonlocality without entanglement in the smallest dimension capable of supporting this phenomenon. On the other hand, the possibility of certification of a measurement obtained from an unextendible product basis has an interesting implication that one can also self-test a bound entangled state in the considered quantum network. Such a possibility does not seem to exist in the standard Bell scenario. Furthermore, we also analyze the robustness of our scheme toward experimental errors.
Phys. Rev. Lett. 134, 190203 (2025)
Quantum correlations in quantum information, Quantum correlations, foundations & formalism, Quantum foundations, Quantum information processing, Quantum information theory
Bayesian Search of Massive Scalar Fields from LIGO-Virgo-KAGRA Binaries
Research article | Alternative gravity theories | 2025-05-16 06:00 EDT
Yiqi Xie, Adrian Ka-Wai Chung, Thomas P. Sotiriou, and Nicolás Yunes
Massive scalar fields are promising candidates for addressing many unresolved problems in fundamental physics. We report the first model-agnostic Bayesian search of massive scalar fields that are nonminimally coupled to gravity in LIGO/Virgo/KAGRA gravitational-wave data. We find no evidence for such fields and place the most stringent upper limits on their coupling for scalar masses $\lesssim 2\times{}{10}^{- 12}\text{ }\text{ }\mathrm{eV}$. We exemplify the strength of these bounds by applying them to massive scalar-Gauss-Bonnet gravity, finding the tightest constraints on the coupling constant to date, $\sqrt{ {\alpha }_{\mathrm{GB}}}\lesssim 1\text{ }\text{ }\mathrm{km}$ for scalar masses $\lesssim {10}^{- 13}\text{ }\text{ }\mathrm{eV}$ to 90% credible level.
Phys. Rev. Lett. 134, 191402 (2025)
Alternative gravity theories, Classical black holes, Gravitational waves
Experimental Observation of Parity-Symmetry-Protected Phenomena in the Quantum Rabi Model with a Trapped Ion
Research article | Cavity quantum electrodynamics | 2025-05-16 06:00 EDT
Xingyu Zhao, Qian Bin, Waner Hou, Yi Li, Yue Li, Yiheng Lin, Xin-You Lü, and Jiangfeng Du
Symmetry is crucial for gaining insights into the fundamental properties of physical systems, bringing possibilities in studying exotic phenomena such as quantum phase transitions and ground-state entanglement. Here, we experimentally simulate a highly controllable extended quantum Rabi model, capable of tuning into the ultrastrong or deep coupling regime, in a spin-motion-coupled trapped ion. We observe that the phonon driven by such a model with ${\mathbb{Z}}_{2}$ symmetry preserved (broken) would experience double (single) excitation in the ultrastrong coupling regime. Quantum phenomena such as strong ground-state entanglement and quantum superposition in systems occur with parity symmetry, and these phenomena disappear following the symmetry breaking. We also find sensitive responses for the two-level system entropy and phonon Wigner function in the deep coupling regime, depending on the parameter across the symmetry transition point. This Letter offers the prospect of exploring symmetry-controlled quantum phenomena and their applications in high-precision quantum technologies.
Phys. Rev. Lett. 134, 193604 (2025)
Cavity quantum electrodynamics, Quantum entanglement, Quantum phase transitions, Quantum simulation, Trapped ions, Rabi model
Quantum Size Effects on Andreev Transport in $\mathrm{Nb}/\mathrm{Au}/\mathrm{Nb}$ Josephson Junctions: A Combined Ab Initio and Experimental Study
Research article | Andreev bound states | 2025-05-16 06:00 EDT
Hiroki Yamazaki, Gábor Csire, Nóra Kucska, Nic Shannon, Balázs Győrffy, Hidenori Takagi, and Balázs Újfalussy
We have measured the critical current density, superconducting coherence length, and superconducting transition temperature of single-domain, epitaxially grown $\mathrm{Nb}(110)/\mathrm{Au}(111)/\mathrm{Nb}(110)$ trilayers, all of which show a nonmonotonic dependence on the thickness of the Au layer. These results are compared with the predictions of a relativistic, ab initio theory, which incorporates superconducting correlations. We find good agreement with experiment, coming from a rich interplay between superconducting proximity and quantum size effects, mediated by Andreev bound states. These results suggest that quantum size effects could provide a systematic method of controlling the transport properties of superconducting multilayers.
Phys. Rev. Lett. 134, 196002 (2025)
Andreev bound states, Josephson effect, Multiband superconductivity, Proximity effect, Quantum wells, Bogoliubov-de Gennes equations, First-principles calculations, Korringa-Kohn-Rostoker method
High Pressure Synthesis of Rubidium Superhydrides
Research article | Chemical bonding | 2025-05-16 06:00 EDT
Mikhail A. Kuzovnikov, Busheng Wang, Xiaoyu Wang, Tomas Marqueño, Hannah A. Shuttleworth, Calum Strain, Eugene Gregoryanz, Eva Zurek, Miriam Peña-Alvarez, and Ross T. Howie
Through laser-heated diamond anvil cell experiments, we synthesize a series of rubidium superhydrides and explore their properties with synchrotron x-ray powder diffraction and Raman spectroscopy measurements, combined with density functional theory calculations. Upon heating rubidium monohydride embedded in ${\mathrm{H}}{2}$ at a pressure of 18 GPa, we form ${\mathrm{RbH}}{9}\text{- }\mathrm{I}$, which is stable upon decompression down to 8.7 GPa, the lowest stability pressure of any known superhydride. At 22 GPa, another polymorph, ${\mathrm{RbH}}{9}\text{- }\mathrm{II}$ is synthesised at high temperature. Unique to the Rb-H system among binary metal hydrides is that further compression does not promote the formation of polyhydrides with higher hydrogen content. Instead, heating above 87 GPa yields ${\mathrm{RbH}}{5}$, which exhibits two polymorphs (${\mathrm{RbH}}{5}\text{- }\mathrm{I}$ and ${\mathrm{RbH}}{5}\text{- }\mathrm{II}$). All of the crystal structures comprise a complex network of quasimolecular ${\mathrm{H}}{2}$ units and ${\mathrm{H}}^{- }$ anions, with ${\mathrm{RbH}}{5}$ providing the first experimental evidence of linear ${\mathrm{H}}_{3}^{- }$ anions.
Phys. Rev. Lett. 134, 196102 (2025)
Chemical bonding, Composition, Crystal phenomena, Crystal structure, Phase transitions, Structural properties
Phase Diagram of the Easy-Axis Triangular-Lattice ${J}{1}\text{- }{J}{2}$ Model
Research article | Density matrix renormalization group | 2025-05-16 06:00 EDT
Cesar A. Gallegos, Shengtao Jiang (蒋晟韬), Steven R. White, and A. L. Chernyshev
The phase diagram of the $S=1/2$ easy-axis triangular-lattice ${J}{1}\text{- }{J}{2}$ model is investigated using the density-matrix renormalization group and analytical insights. We find a significant spin-liquid region extending from the Heisenberg limit and residing between the Y phase—known as the magnetic analogue of the ‘’supersolid’’—and collinear stripe phase. The order parameters of the supersolid are analyzed and an understanding of its lack of a ferromagnetic moment is suggested.
Phys. Rev. Lett. 134, 196702 (2025)
Density matrix renormalization group, Frustrated magnetism, Magnetic order, Magnetic phase transitions, Phase diagrams, Quantum spin liquid, Spin liquid, Antiferromagnets, Strongly correlated systems, Triangular lattice
Weak Ferromagnetism in Altermagnets from Alternating $g$-Tensor Anisotropy
Research article | Altermagnetism | 2025-05-16 06:00 EDT
Daegeun Jo, Dongwook Go, Yuriy Mokrousov, Peter M. Oppeneer, Sang-Wook Cheong, and Hyun-Woo Lee
Altermagnets are magnetic materials with antiferromagnetic spin ordering but exhibit ferromagnetic properties. Understanding the microscopic origin of the latter is a central problem. Ferromagnetlike properties such as the anomalous Hall effect are linked with weak ferromagnetism, whose microscopic origin in altermagnets remains unclear however. We show theoretically that the alternating $g$-tensor anisotropy in altermagnets can induce weak orbital ferromagnetism even when the Dzyaloshinskii-Moriya interaction is forbidden. We demonstrate this mechanism to explain weak ferromagnetism for both collinear and noncollinear spin altermagnets. Our findings provide new insights into the origin of weak ferromagnetism and suggest orbital-based ways for manipulating magnetic configurations in altermagnets.
Phys. Rev. Lett. 134, 196703 (2025)
Altermagnetism, Magnetism, Spin-orbit coupling, Altermagnets, Tight-binding model
Inherent Circular Dichroism of Phonons in Magnetic Weyl Semimetal ${\mathrm{Co}}{3}{\text{Sn}}{2}{\mathrm{S}}_{2}$
Research article | Electron-phonon coupling | 2025-05-16 06:00 EDT
R. Yang, Y.-Y. Zhu, M. Steigleder, Y.-C. Liu, C.-C. Liu, X.-G. Qiu, Tiantian Zhang, and M. Dressel
We investigated the infrared-active phonons in ferromagnetic Weyl semimetal ${\mathrm{Co}}{3}{\text{Sn}}{2}{\mathrm{S}}{2}$ using optical spectroscopy. Below the Curie temperature (${T}{C}\approx 175\text{ }\text{ }\mathrm{K}$), we observed asymmetric Fano line shapes of phonons peaks in the optical conductivities, reflecting the presence of electron-phonon coupling. Additionally, the detected phonon signals by the polar Kerr rotation and the ellipticity spectroscopy indicate the circular dichroism (CD) of phonons. We attribute the CD of phonons to their distinct couplings with charge excitations on the tilted Weyl nodal rings in two circularly polarized channels. Our findings provide experimental evidence that, without external fields, phonons can also become circularly polarized by coupling with the electronic topology. Since the magnetic exchange splitting gradually shifts the topological bands in ${\mathrm{Co}}{3}{\text{Sn}}{2}{\mathrm{S}}_{2}$, the CD of phonons exhibits significant temperature dependence, hinting at a promising approach for manipulation.
Phys. Rev. Lett. 134, 196905 (2025)
Electron-phonon coupling, Optical phonons, Weyl semimetal, Chiral symmetry, Infrared spectroscopy, Kerr effect
Magnetic Order Induced Chiral Phonons in a Ferromagnetic Weyl Semimetal
Research article | Topological materials | 2025-05-16 06:00 EDT
Mengqian Che, Jinxuan Liang, Yunpeng Cui, Hao Li, Bingru Lu, Wenbo Sang, Xiang Li, Xuebin Dong, Le Zhao, Shuai Zhang, Tao Sun, Wanjun Jiang, Enke Liu, Feng Jin, Tiantian Zhang, and Luyi Yang
Chiral phonons are vibrational modes in a crystal that possess a well-defined handedness or chirality, typically found in materials that lack inversion symmetry. Here, we report the discovery of chiral phonon modes in the kagome ferromagnetic Weyl semimetal ${\mathrm{Co}}{3}{\mathrm{Sn}}{2}{\mathrm{S}}{2}$, a material that preserves inversion symmetry but breaks time-reversal symmetry. Using helicity-resolved magneto-Raman spectroscopy, we observe the spontaneous splitting of the doubly degenerate in-plane ${E}{g}$ modes into two distinct chiral phonon modes of opposite helicity when the sample is zero-field cooled below the Curie temperature in the absence of an external magnetic field. As we sweep the out-of-plane magnetic field, this ${E}_{g}$ phonon splitting exhibits a well-defined hysteresis loop directly correlated with the material’s magnetization. The observed spontaneous splitting reaches up to $1.27\text{ }\text{ }{\mathrm{cm}}^{- 1}$ at low temperatures, progressively diminishes with increasing temperature, and completely vanishes near the Curie temperature. Our findings highlight the role of the magnetic order in inducing chiral phonons, paving the way for novel methods to manipulate chiral phonons through magnetization and vice versa. Additionally, our Letter introduces new possibilities for controlling chiral Weyl fermions using chiral phonons.
Phys. Rev. Lett. 134, 196906 (2025)
Topological materials, Ferromagnets, Light scattering
Optical Signatures of Spin Symmetries in Unconventional Magnets
Research article | Magnetism | 2025-05-16 06:00 EDT
Javier Sivianes, Flaviano José dos Santos, and Julen Ibañez-Azpiroz
The concept of spin symmetries has gained renewed interest as a valuable tool for classifying unconventional magnetic phases, including altermagnets and recently identified $p$-wave magnets. In this work, we show that in compounds with weak spin-orbit coupling, the dominant spin and charge photoresponse is determined by spin group rather than the conventional magnetic group symmetry. As a concrete realization we consider the nonlinear shift photocurrent in ${\mathrm{Mn}}{5}{\mathrm{Si}}{3}$, a material that features the two possible classes of unconventional $p$-wave magnetism in the form of two competing spin structures, a coplanar and noncoplanar one. While both are predicted to generate shift currents based on magnetic symmetry considerations, only the noncoplanar configuration survives the spin symmetry requirements. This is numerically confirmed by our ab initio calculations, providing a protocol to experimentally identify the spin configuration of this promising material in photogalvanic or transport measurements.
Phys. Rev. Lett. 134, 196907 (2025)
Magnetism, Photocurrent, Magnetic systems, Noncollinear magnets, Nonlinear optical materials, P-symmetry, T-symmetry
Persistence Exponents of Self-Interacting Random Walks
Research article | Brownian motion | 2025-05-16 06:00 EDT
J. Brémont, L. Régnier, R. Voituriez, and O. Bénichou
The persistence exponent, which characterizes the long-time decay of the survival probability of stochastic processes in the presence of an absorbing target, plays a key role in quantifying the dynamics of fluctuating systems. Determining this exponent for non-Markovian processes is known to be a difficult task, and exact results remain scarce despite sustained efforts. In this Letter, we consider the fundamental class of self-interacting random walks (SIRWs), which display long-range memory effects that result from the interaction of the random walker at time $t$ with the territory already visited at earlier times ${t}^{‘ }<t$. We compute exactly the persistence exponent for all physically relevant SIRWs. As a byproduct, we also determine the splitting probability of these processes. Besides their intrinsic theoretical interest, these results provide a quantitative characterization of the exploration process of SIRWs, which are involved in fields as diverse as foraging theory, cell biology, and nonreversible Monte Carlo methods.
Phys. Rev. Lett. 134, 197103 (2025)
Brownian motion, Classical statistical mechanics, Random walks
Mesoscopic Theory for Coupled Stochastic Oscillators
Research article | Coupled oscillators | 2025-05-16 06:00 EDT
Victor Buendía
The celebrated Ott-Antonsen Ansatz for coupled oscillators provides a useful framework for working with deterministic systems in the thermodynamic limit, but it fails to capture many features of stochastic systems. Several solutions have been recently proposed to accurately describe the behavior of the order parameters in coupled oscillator systems. However, a fluctuating description of such order parameters has been still elusive. In this Letter, I construct for the first time a general mesoscopic description of finite-size populations of oscillators subject to white noise. The theory allows one to derive Langevin equations for the Kuramoto-Daido order parameters, opening the door to study features of synchronization phase transitions and finite-size effects, which were inaccessible before. The analysis of the fluctuations in the stochastic Kuramoto model uncovered highly accurate, closed analytical expressions for the average Kuramoto order parameter which outperforms previous approaches.
Phys. Rev. Lett. 134, 197201 (2025)
Coupled oscillators, Critical phenomena, Fluctuations & noise, Stochastic processes, Synchronization, Synchronization transition
Mechanics of Soft-Body Rolling Motion without External Torque
Research article | Bending | 2025-05-16 06:00 EDT
Xudong Liang, Yimiao Ding, Zihao Yuan, Yuxuan Han, Yutang Zhou, Junqi Jiang, Zongling Xie, Peng Fei, Yixuan Sun, Pan Jia, Guoying Gu, Zheng Zhong, Feifei Chen, Guangwei Si, and Zhefeng Gong
A study of the rolling motion of fruit-fly larvae has enabled researchers to create a soft robot that can rotate by itself.
Phys. Rev. Lett. 134, 198401 (2025)
Bending, Cellular organization, physiology & dynamics, Elastic deformation, Friction, Locomotion, Mechanical deformation, Elastomers, Insects, Muscle, Additive manufacturing, Imaging & optical processing, Laser ablation
Physical Review X
Topologically Protected Flatness in Chiral Moiré Heterostructures
Research article | Flat bands | 2025-05-16 06:00 EDT
Valentin Crépel, Peize Ding, Nishchhal Verma, Nicolas Regnault, and Raquel Queiroz
Flat bands in twisted bilayer graphene at the first magic angle remain robust under disorder owing to a hidden symmetry, offering topological protection not found at higher angles.
Phys. Rev. X 15, 021056 (2025)
Flat bands, Random & disordered media, Transition metal dichalcogenides, Twisted bilayer graphene, Twisted heterostructures
Practical Quantum Advantage on Partially Fault-Tolerant Quantum Computer
Research article | Quantum computation | 2025-05-16 06:00 EDT
Riki Toshio, Yutaro Akahoshi, Jun Fujisaki, Hirotaka Oshima, Shintaro Sato, and Keisuke Fujii
A new framework shows how to achieve practical quantum advantage using early fault-tolerant quantum computing devices equipped with only tens of thousands of qubits.
Phys. Rev. X 15, 021057 (2025)
Quantum computation, Quantum error correction, Quantum simulation, Surface code quantum computing
arXiv
Folded State Dynamics – A Geometric and Deterministic Origin of Irreversibility
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-05-16 20:00 EDT
The emergence of irreversibility in isolated, deterministic systems remains a central challenge in statistical mechanics. Traditional approaches, such as Boltzmann’s H-theorem and Lanford’s derivation of the Boltzmann equation, rely on probabilistic assumptions and are limited to dilute gases and short timescales. We introduce Folded State Dynamics (FSD), a framework in which irreversibility arises from the geometric structure of phase space in systems with coupled rotational and translational degrees of freedom. In contrast to conventional models with unfolded, weakly coupled modes, FSD exhibits phase space folding, where deterministic coupling induces instability and chaotic mixing. We show that equilibrium states exponentially dominate the accessible phase space volume, while constrained configurations (e.g., pure rotation) occupy measure-zero subsets. This yields a geometric derivation of entropy growth, with reversal probabilities suppressed as Prev and recurrence times Trec, resolving Loschmidt’s and Zermelo’s objections without coarse-graining or fine-tuning. FSD is further extended to include charged systems (cFSD), where electromagnetic interactions continuously drive phase space folding. FSD thus offers a deterministic and testable mechanism for irreversibility, with implications ranging from confined colloids to the cosmological arrow of time
Statistical Mechanics (cond-mat.stat-mech), History and Philosophy of Physics (physics.hist-ph)
Quantum Hall Effect without Chern Bands
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Benjamin Michen, Jan Carl Budich
The quantum Hall effect was originally observed in a two-dimensional electron gas forming Landau levels when exposed to a strong perpendicular magnetic field, and has later been generalized to Chern insulators without net magnetization. Here, further extending the realm of the quantum Hall effect, we report on the robust occurrence of an integer quantized transverse conductance at the onset of disorder in a microscopic lattice model all bands of which are topologically trivial (zero Chern number). We attribute this remarkable phenomenon to the energetic separation of substantial but non-quantized Berry fluxes within the topologically trivial bands. Adding a random disorder potential then nudges the system into a stable quantum Hall phase from an extended critical regime of the clean system obtained by placing the Fermi energy within a broad window in either of the trivial bands. Our results are corroborated by extensive numerical transport simulations as well as the analysis of several complementary topological markers.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Disordered Systems and Neural Networks (cond-mat.dis-nn), Quantum Physics (quant-ph)
6+10 pages, 4+5 figures
Euler topology in classical spin liquids
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
Luca Rüegg, Arthur Morris, Han Yan, Robert-Jan Slager
Classical spin liquids have recently been analyzed in view of the single-gap homotopy classification of their dispersive eigenvectors. We show that the recent progress in defining multi-gap topologies, notably exemplified by the Euler class, can be naturally included in these homotopy-based classification schemes and present phases that change topology by band node braiding. This process alters the topology of the pinch points in the spin structure factor and consequently their stability. Furthermore, we discuss how these notions also pertain to models discussed previously in the literature and have a broader range of application beyond our specific results. Our work thus opens up an uncharted avenue in the understanding of spin liquids.
Strongly Correlated Electrons (cond-mat.str-el), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Statistical Mechanics (cond-mat.stat-mech)
6+3 pages, 4+1 figures
Full, three-quarter, half and quarter Wigner crystals in Bernal bilayer graphene
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
Enrique Aguilar-Méndez, Titus Neupert, Glenn Wagner
Application of a displacement field opens a gap and enhances the Van-Hove singularities in the band structure of Bernal-stacked bilayer graphene. By adjusting the carrier density so that the Fermi energy lies in the vicinity of these singularities, recent experiments observe a plethora of highly correlated electronic phases including isospin polarized phases and high-resistance states with non-linear electric transport indicative of a possible Wigner crystal. We perform Hartree-Fock calculations incorporating long-range Coulomb interactions and allowing for translational and rotational symmetry breaking. We obtain the displacement field vs. carrier density phase diagram which shows isospin polarized metallic phases tracking the Van-Hove singularity in the valence band. Between these metallic phases we observe regions where the ground state is a Wigner crystal. The isospin polarization of the Wigner crystals tracks the isospin polarization of the nearby metallic phases. Depending on whether we have four, three, two or one isospin flavours, we obtain a full, three-quarter, half or quarter Wigner crystal.
Strongly Correlated Electrons (cond-mat.str-el), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Stable Real-Space Invariants and Topology Beyond Symmetry Indicators
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Yoonseok Hwang, Vaibhav Gupta, Frank Schindler, Luis Elcoro, Zhida Song, B. Andrei Bernevig, Barry Bradlyn
We show that certain band gaps, which appear topologically trivial from the perspective of symmetry indicators (SIs), must instead be topological, as guaranteed by real-space information that follows from Topological Quantum Chemistry (TQC). To address this, we introduce stable real-space invariants (SRSIs) that generalize the previously discovered local and composite real-space invariants to global topological invariants of a given set of bands. These are linear combinations of Wannier state multiplicities at Wyckoff positions and take the form of $ \mathbb{Z}$ - and $ \mathbb{Z}_n$ -valued quantities ($ n=2,4$ ). We enumerate all $ \mathbb{Z}$ SRSIs and $ \mathbb{Z}_n$ SRSIs in all non-magnetic space groups (SGs) with and without spin-orbit coupling. SRSIs fully diagnose the stable equivalence of atomic insulators, ensuring that two atomic insulators with matching SRSIs are adiabatically deformable to one another in the presence of auxiliary trivial bands. For both atomic and topological bands, $ \mathbb{Z}$ SRSIs are determined by the momentum-space symmetry data and thus determine the SIs. $ \mathbb{Z}_n$ SRSIs provide additional information about trivial band structures not captured by momentum-space data. While split elementary band representations (EBRs), where the bands forming an EBR split into disconnected parts, must induce band topology, there are 211 cases across 51 SGs where the momentum-space data of an EBR decomposes linearly with positive integer coefficients into those of other EBRs. We demonstrate that $ \mathbb{Z}_n$ SRSIs successfully identify the band topology in the majority of these split EBR cases, diagnosing all but 8 cases in 5 SGs. Our results solidify the conceptual framework of TQC as containing, but going beyond, SIs and momentum-space symmetry data.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci)
11+140 pages, 3+5 figures
Towards Atomic-Scale Control over Structural Modulations in Quasi-1D Chalcogenides for Colossal Optical Anisotropy
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Guodong Ren, Shantanu Singh, Gwan Yeong Jung, Wooseon Choi, Huandong Chen, Boyang Zhao, Kevin Ye, Andrew R. Lupini, Miaofang Chi, Jordan A. Hachtel, Young-Min Kim, Jayakanth Ravichandran, Rohan Mishra
Optically anisotropic materials are sought after for tailoring the polarization of light. Recently, colossal optical anisotropy was reported in a quasi-one-dimensional chalcogenide, Sr1.125TiS3. Compared to SrTiS3, the excess Sr in Sr1.125TiS3 leads to periodic structural modulations and introduces additional electrons that undergo charge ordering on select Ti atoms to form a highly polarizable cloud oriented along the c-axis, hence, resulting in the colossolal optical anisotropy. Here, further enhancement of the colossal optical anisotropy to 2.5 in Sr1.143TiS3 is reported through control over the periodicity of the atomic-scale modulations. The role of structural modulations in tuning the optical properties in a series of SrxTiS3 compounds has been investigated using DFT calculations. The structural modulations arise from various stacking sequences of face-sharing TiS6 octahedra and twist-distorted trigonal prisms, and are found to be thermodynamically stable for x larger than 1 but smaller than 1.5. As x increases, an indirect-to-direct band gap transition is predicted for x equal to and larger than 1.143 along with an increased occupancy of Ti-dz2 states. Together, these two factors result in a theoretically predicted maximum birefriengence of 2.5 for Sr1.143TiS3. Single crystals of Sr1.143TiS3 were grown using a molten-salt flux method. Atomic-scale observations using scanning transmission electron microscopy confirm the feasibility of synthesizing SrxTiS3 with varied modulation periodicities. Overall, these findings demonstrate compositonal tunability of optical properties in SrxTiS3 compounds, and potentially in other hexagonal perovskites having structural modulations.
Materials Science (cond-mat.mtrl-sci)
Role of structural biaxiality on the phase behaviour of chiral liquid crystals
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-05-16 20:00 EDT
Sayantan Mondal, Jayashree Saha
We report a computer simulation study on the effect of molecular structural biaxiality in the phase formation of chiral molecules. In this study, we have done coarse-grained modeling to observe self-assembled phase behavior. In our molecular dynamics simulation study we varied both the chiral interaction strength and molecular biaxiality. Uniaxial molecules give rise to cholesteric phase, blue phase whereas molecular biaxiality favours cholesteric phase. At higher chirality, small chiral domains are formed creating twisted cylindrical networks with each cylinder having elliptical cross-sections instead of circular nature as found in uniaxial systems. The value of cholesteric pitch decreases when chirality and molecular biaxiality becomes higher. Coaction of biaxiality and chirality is crucial for fabricating liquid crystal materials with optical properties suitable for displays, sensors and chiral photonic devices.
Soft Condensed Matter (cond-mat.soft)
9 pages, 7 figures
Geometric Origin of Phonon Magnetic Moment in Dirac Materials
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Wenqin Chen, Xiao-Wei Zhang, Ting Cao, Shi-Zeng Lin, Di Xiao
We develop a theory for the phonon magnetic moment in doped Dirac materials, treating phonons as emergent gauge and gravitational fields coupled to Dirac fermions in curved space. By classifying electron-phonon coupling into angular momentum channels of Fermi surface deformation, we show that the phonon moment arises from two mechanisms: proportional to the electron Hall conductivity through the emergent gauge field coupling, and to the Hall viscosity through the frame field coupling. Applying our theory to Cd$ _3$ As$ _2$ with first-principles calculations, we find quantitative agreement with experiment. Our results reveal a general mechanism for dynamically generating large phonon magnetism in metals and suggest a new route for probing Hall viscosity via phonon dynamics.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
5 pages, 2 figures
A Mobile Impurity in the Kitaev Chain: Phase Diagram and Signatures of Topology
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
A.V. Sadovnikov, M.S. Bahovadinov, A.N. Rubtsov, A.A. Markov
We study the physics of a mobile impurity immersed in a $ 1d$ topological superconductor. We discuss the system’s phase diagram obtained with exact diagonalization. We argue that the character of the transition from a weak to strong coupling regime depends on the phase of the host superconductor. A smooth crossover between a weakly coupled polaron and a molecular state is observed in the topological phase. In contrast, the impurity undergoes a sharp phase transition in a topologically trivial background.
Strongly Correlated Electrons (cond-mat.str-el), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Extrinsic contribution to bosonic thermal Hall transport
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
Léo Mangeolle, Johannes Knolle
Bosonic excitations like phonons and magnons dominate the low-temperature transport of magnetic insulators. Similar to electronic Hall responses, the thermal Hall effect (THE) of charge neutral bosons has been proposed as a powerful tool for probing topological properties of their wavefunctions. For example, the intrinsic contribution of the THE of a perfectly clean system is directly governed by the distribution of Berry curvature, and many experiments on topological magnon and phonon insulators have been interpreted in this way. However, disorder is inevitably present in any material and its contribution to the THE has remained poorly understood. Here we develop a rigorous kinetic theory of the extrinsic side-jump contribution to the THE of bosons. We show that the extrinsic THE can be of the same order as the intrinsic one but sensitively depends on the type of local imperfection. We study different types of impurities and show that a THE can even arise as a pure impurity-induced effect in a system with a vanishing intrinsic contribution. As a side product, we also generalize existing results for the electronic AHE to general types of impurities beyond the standard assumption of local potential scattering. We discuss the importance of our results for the correct interpretation of THE measurements.
Strongly Correlated Electrons (cond-mat.str-el), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Statistical Mechanics (cond-mat.stat-mech)
14 + 10 pages, 2 figures
Brownian Dynamics Simulations of Inclusions in an Active Fluid Bath
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-05-16 20:00 EDT
Lijie Ding, Robert A. Pelcovits, Thomas R. Powers
We carry out two-dimensional Brownian dynamics simulations of the behavior of rigid inclusion particles immersed in an active fluid bath. The active fluid is modeled as a collection of self-propelled circular disks interacting via a soft repulsive potential and a nematic alignment interaction. The fluid is characterized by its nematic order, polar order and orientational correlation length. The active fluid bath transitions from the isotropic to the nematic phase with increasing number density, increasing nematic interaction strength or increasing Péclet number. The inclusion particles are modeled as rigid assemblies of passive circular disks. Four types of inclusions are considered: a rod-like $ I$ shape, a boomerang-like $ L$ shape, and stair-like shapes $ Z$ and $ Z^\ast$ , with opposite handedness. When inclusions are introduced into the active fluid bath, their diffusion is significantly enhanced by the force and torque exerted by the active fluid particles and the chiral inclusion particles exhibit constant rotational drift. These diffusion and rotation enhancements increase as the swimming speed of the active fluid particles increases. The translational motion of the inclusion particles also couples with their orientational motion, and the correlation is modulated by the active fluid particles’ swimming speed. This work paves the way for future simulations of inclusions in active fluid baths and suggests potential avenues for controlling transport properties in active materials.
Soft Condensed Matter (cond-mat.soft), Computational Physics (physics.comp-ph)
12 pages, 10 figures
Tunable and Persistent Polarization in Centrosymmetric Oxides
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
D.-S. Park, N. Pryds, N. Gauquelin, M. Hadad, D. Chezganov, A. Palliotto, D. Jannis, J. Íñiguez-González, J. Verbeeck, P. Muralt, D. Damjanovic
Introducing symmetry breaking in materials enables the emergence of functionalities. This can be microscopically and macroscopically driven by applying external stimuli such as mechanical stress, electric field, temperature, and chemical modification. For instance, non-zero net dipole moments are formed in a material with the presence of local charged defects or their clusters, which can alter the crystal structure, charge states, and electrostatic potential across the material. Here, we demonstrate a conceptual approach to defects-mediated symmetry breaking that allows for built-in polarization in a centrosymmetric oxide, $ \mathrm{Gd}x\mathrm{Ce}{1-x}\mathrm{O}_{2-\delta}$ (CGO) films, via creating a macroscopic charge asymmetry. Our results show that switchable and enduring polarization in CGO films is governed by the redistribution of oxygen vacancies. This leads to notable and persistent pyroelectric effects with coefficient of approximately 180 $ \mu\mathrm{C}\cdot\mathrm{m}^{-2}\cdot\mathrm{K}^{-1}$ . Our findings highlight the potential to develop high-performance, sustainable, environmentally friendly polar film materials by manipulating ionic defects from their centrosymmetric ground states. This approach provides new opportunities to expand polar materials in current and future energy and electronic applications.
Materials Science (cond-mat.mtrl-sci)
Emergent chirality and enantiomeric selectivity in layered NbOX$_2$ crystals
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Martin Gutierrez-Amigo, Claudia Felser, Ion Errea, Maia G. Vergniory
The spontaneous emergence of chirality in crystalline solids has profound implications for electronic, optical, and topological properties, making the control of chiral phases a central challenge in materials design. Here, we investigate the structural and electronic properties of a new family of layered compounds, $ \mathrm{NbOX_2}$ , and explore the connection between their achiral $ I m m m$ phase and chiral $ C 2$ phase. Through first-principles calculations, we identify an intermediate achiral $ C 2/m$ phase that bridges the high- and low-symmetry phases within a three-dimensional order parameter space. The insulating $ C 2$ phase exhibits unique electronic properties, including flat Niobium $ d$ -orbital bands near the Fermi level associated with an obstructed atomic limit (OAL), hosting topologically non-trivial surface states under specific cleavage conditions. By analyzing the Born-Oppenheimer energy surfaces (BOES), we find that the shallow energy minima of the $ C 2$ phase suggest that the intermediate $ C 2/m$ phase may be stabilized either by ionic quantum or thermal fluctuations, and the consequent lattice anharmonicity, or by external factors such as pressure. Additionally, we show how an external electric field, by breaking the necessary symmetries, biases the system toward a preferred chirality by lifting the energy degeneracy between the two enantiomers. This, combined with the small energy barrier between the enantiomers in the $ C 2$ phase, enables handedness control and allows us to propose a mechanism for selective handedness stabilization by leveraging electric fields and temperature-dependent anharmonic effects. Our findings establish a framework for understanding chirality emergence in layered materials and offer a pathway for designing systems with tunable enantiomeric populations.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Other Condensed Matter (cond-mat.other)
16 pages, 10 figures
Charge density waves and soft phonon evolution in the superconductor BaNi$2$(As${1-x}$P$_x$)$_2$
New Submission | Superconductivity (cond-mat.supr-con) | 2025-05-16 20:00 EDT
Tom Lacmann, Sofia-Michaela Souliou, Fabian Henssler, Mehdi Frachet, Philippa Helen McGuinness, Michael Merz, Björn Wehinger, Daniel A. Chaney, Amir-Abbas Haghighirad, Rolf Heid, Matthieu Le Tacon
The superconductor BaNi$ _2$ As$ _2$ exhibits a soft-phonon-driven, incommensurate charge density wave (I-CDW) which is accompanied by a small orthorhombic structural phase transition. Upon further cooling, BaNi$ _2$ As$ _2$ undergoes a first-order structural transition to a triclinic phase in which a commensurate CDW (C-CDW) appears. The relationship and interplay between the I-CDW, C-CDW and structural phase transitions has remained elusive. To investigate this issue, we present a complementary study of thermal diffuse X-Ray scattering and inelastic X-Ray scattering for phosphorus substituted BaNi$ _2$ (As$ _{1-x}$ P$ _x$ )$ _2$ $ (x\lessapprox0.12)$ and down to 2.2 K. We show that most of the diffuse scattering signal can be well described by first-principles lattice dynamics calculations. Furthermore, we find that although phosphorus substitution rapidly suppresses the structural transition temperatures, the temperature dependence of the correlation length of the I-CDW fluctuations and the formation of Bragg-like superstructure peaks associated with long-range ordering of this order depends only weakly on the substitution level. Finally, we present the absence of signatures of the I-CDW to C-CDW or triclinic transition in the lattice dynamics, indicating that these instabilities are not (soft) phonon driven.
Superconductivity (cond-mat.supr-con), Strongly Correlated Electrons (cond-mat.str-el)
11 pages, 8 figures, 13 pages supplemental material, 12 supplementary figures
Reduction of fully screened magnetoplasmons in a laterally confined anisotropic two-dimensional electron system to an isotropic one
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
D. A. Rodionov, I. V. Zagorodnev
We investigate the properties of natural two-dimensional (2D) magnetoplasma modes in laterally confined electron systems, such as 2D materials, quantum wells, or inversion layers in semiconductors, with an elliptic Fermi surface. The conductivity of the system is considered in a dynamical anisotropic Drude model. The problem is solved in the fully screened limit, i.e., under the assumption that the distance between the two-dimensional electron system and the nearby metal gate is small compared to all other lengths in the system, including the wavelength of plasmons. Remarkably, in this limit plasma oscillations in an anisotropic 2D confined system are equivalent to plasma oscillations in an isotropic 2D electron system obtained by some stretching, even when the electromagnetic retardation is taken into account. Moreover, accounting for electromagnetic retardation leads only to a renormalization of the effective masses of carriers, somewhat like in relativity. As an example, we reduce the equations describing plasmons in a gated disk with an anisotropic two-dimensional electron gas to the equations describing oscillations in an isotropic ellipse. Without a magnetic field, we solve them analytically and find eigenfrequencies. To find a solution in a magnetic field, we expand the current of plasma oscillations in the complete set of Mathieu functions. Leaving the leading terms of the expansion, we approximately find and analyze magnetodispersion for the lowest modes.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Unconventional polaronic ground state in superconducting LiTi$_2$O$_4$
New Submission | Superconductivity (cond-mat.supr-con) | 2025-05-16 20:00 EDT
Zubia Hasan, Grace A. Pan, Harrison LaBollita, Austin Kaczmarek, Suk Hyun Sung, Shekhar Sharma, Purnima P. Balakrishnan, Edward Mercer, Vivek Bhartiya, Zaher Salman, Thomas Prokscha, Andreas Suter, Alexander J. Grutter, Mirian Garcia-Fernandez, Ke-Jin Zhou, Jonathan Pelliciari, Valentina Bisogni, Ismail El Baggari, Darrell G. Schlom, Matthew R. Barone, Charles M. Brooks, Katja C. Nowack, Antia S. Botana, Brendan D. Faeth, Alberto de la Torre, Julia A. Mundy
Geometrically frustrated lattices can display a range of correlated phenomena, ranging from spin frustration and charge order to dispersionless flat bands due to quantum interference. One particularly compelling family of such materials is the half-valence spinel Li$ B_2$ O$ _4$ materials. On the $ B$ -site frustrated pyrochlore sublattice, the interplay of correlated metallic behavior and charge frustration leads to a superconducting state in LiTi$ _2$ O$ _4$ and heavy fermion behavior in LiV$ _2$ O$ _4$ . To date, however, LiTi$ _2$ O$ _4$ has primarily been understood as a conventional BCS superconductor despite a lattice structure that could host more exotic groundstates. Here, we present a multimodal investigation of LiTi$ _2$ O$ _4$ , combining ARPES, RIXS, proximate magnetic probes, and ab-initio many-body theoretical calculations. Our data reveals a novel mobile polaronic ground state with spectroscopic signatures that underlie co-dominant electron-phonon coupling and electron-electron correlations also found in the lightly doped cuprates. The cooperation between the two interaction scales distinguishes LiTi$ _2$ O$ _4$ from other superconducting titanates, suggesting an unconventional origin to superconductivity in LiTi$ _2$ O$ _4$ . Our work deepens our understanding of the rare interplay of electron-electron correlations and electron-phonon coupling in unconventional superconducting systems. In particular, our work identifies the geometrically frustrated, mixed-valence spinel family as an under-explored platform for discovering unconventional, correlated ground states.
Superconductivity (cond-mat.supr-con), Strongly Correlated Electrons (cond-mat.str-el)
Lean CNNs for mapping electron charge density fields to material properties
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Pranoy Ray, Kamal Choudhury, Surya R. Kalidindi
This work introduces a lean CNN (convolutional neural network) framework, with a drastically reduced number of fittable parameters (<81K) compared to the benchmarks in current literature, to capture the underlying low-computational cost (i.e., surrogate) relationships between the electron charge density (ECD) fields and their associated effective properties. These lean CNNs are made possible by adding a pre-processing step (i.e., a feature engineering step) that involves the computation of the ECD fields’ spatial correlations (specifically, 2-point spatial correlations). The viability and benefits of the proposed lean CNN framework are demonstrated by establishing robust structure-property relationships involving the prediction of effective material properties using the feature-engineered ECD fields as the only input. The framework is evaluated on a dataset of crystalline cubic systems consisting of 1410 molecular structures spanning 62 different elemental species and 3 space groups.
Materials Science (cond-mat.mtrl-sci), Disordered Systems and Neural Networks (cond-mat.dis-nn), Applied Physics (physics.app-ph)
Integrating Materials and Manufacturing Innovation, 1-13 (2025)
Strain-Gradient and Curvature-Induced Changes in Domain Morphology of BaTiO3 Nanorods: Experimental and Theoretical Studies
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Olha A. Kovalenko, Eugene A. Eliseev, Yuriy O. Zagorodniy, Srečo Davor Škapin, Marjeta Maček Kržmanc, Lesya Demchenko, Valentyn V. Laguta, Zdravko Kutnjak, Dean R. Evans, Anna N. Morozovska
We investigate the impact of OH- ions incorporation on the lattice strain and spontaneous polarization of BaTiO3 nanorods synthesized under different conditions. It was confirmed that the lattice strain depends directly on Ba supersaturation, with higher supersaturation leading to an increase in the lattice strain. However, it was shown that crystal growth and observed lattice distortion are not primarily influenced by external strain; rather, OH- ions incorporation plays a key role in generating internal chemical strains and driving these processes. By using the less reactive TiO2 precursor instead of TiOCl2 and controlling Ba supersaturation, the slower nucleation rate enables more effective regulation of OH- ions incorporation and crystal growth. This in turn effects both particle size and lattice distortion, leading to c/a ratio of 1.013 - 1.014. The incorporation of OH- ions induces lattice elongation along the c-axis, contributing to anisotropic growth, increasing of the rod diameter and their growth-induced bending. However, the possibility of the curvature-induced changes in domain morphology of BaTiO3 nanorods remains almost unexplored. To study the possibility, we perform analytical calculations and finite element modeling, which provide insights into the curvature-induced changes in the strain-gradient, polarization distribution, and domain morphology in BaTiO3 nanorods. Theoretical results reveal the appearance of the domain stripes in BaTiO3 nanorod when the curvature exceeds a critical angle. The physical origin of the domain stripes emergence is the tendency to minimize its elastic energy of the nanorod by the domain splitting. These findings suggest that BaTiO3 nanorods, with curvature-controllable amount of domain stripes, could serve as flexible race-track memory elements for flexo-tronics and domain-wall electronics.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
37 pages, including 11 figures and 3 Appendices
Deep-Learning Atomistic Pseudopotential Model for Nanomaterials
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Kailai Lin, Matthew J. Coley-O’Rourke, Eran Rabani
The semi-empirical pseudopotential method (SEPM) has been widely applied to provide computational insights into the electronic structure, photophysics, and charge carrier dynamics of nanoscale materials. We present “DeepPseudopot”, a machine-learned atomistic pseudopotential model that extends the SEPM framework by combining a flexible neural network representation of the local pseudopotential with parameterized non-local and spin-orbit coupling terms. Trained on bulk quasiparticle band structures and deformation potentials from GW calculations, the model captures many-body and relativistic effects with very high accuracy across diverse semiconducting materials, as illustrated for silicon and group III-V semiconductors. DeepPseudopot’s accuracy, efficiency, and transferability make it well-suited for data-driven in silico design and discovery of novel optoelectronic nanomaterials.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
A Framework for Identifying Non-van der Waals 2D Materials
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Two-dimensional (2D) materials are categorized into van der Waals (vdW) and non-vdW types. However, no relevant descriptors have been proposed for identifying the latter. Here, we identify the non-vdW 2D materials by calculating the thickness-dependence of total energy of thin films truncated from surfaces. The non-vdW 2D materials exhibit a deviation from the law of exfoliation energy inverse to the number of layers in the monolayer limit. This framework is applied to explore single- and multi-component systems, which predicts the synthesizability of several non-vdW 2D materials including silicene and goldene that are overlooked in the dimensional analysis of the parent crystals and also predicts that a Janus structure exists in nature but is hidden in 3D crystals.
Materials Science (cond-mat.mtrl-sci)
6 pages, 5 figures
Strain-induced gyrotropic effects in ferroelectric BaTiS3
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Wei Luo, Asier Zabalo, Guodong Ren, Gwan-Yeong Jung, Massimiliano Stengel, Rohan Mishra, Jayakanth Ravichandran, Laurent Bellaiche
Gyrotropic effects, including natural optical activity (NOA) and the nonlinear anomalous Hall effect (NAHE), are crucial for advancing optical and transport devices. We explore these effects in the BaTiS3 system, a quasi-one-dimensional crystal that exhibits giant optical anisotropy. (Niu et al. Nat. Photonics 12, 392 (2018); Zhao et al. Chem. Mater. 34, 5680 (2022)). In the P63cm phase which is stable under room temperature, we predict two distinct strain-induced phase transitions: a symmetry-lowering transition from the P63cm to P63 phase under tensile strain, which enhances NOA and enables optical rotation; and an isostructural insulator-to-polar Weyl semimetal (WSM) transition under compressive strain, which activates the NAHE and exhibits a strain-induced sign reversal. The low-temperature P21 phase also transforms into a P212121 phase under enough compressive strains with such phase transition exhibiting a large NOA. All these results highlight BaTiS3 as a viable candidate for novel ferroelectrics, optical and transport devices with strain enhanced or activated gyrotropic properties.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
18 pages, 4 figures
Gapless spinon excitations emerging from a multipolar transverse field in the triangular-lattice Ising antiferromagnet NaTmSe2
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
Zheng Zhang, Jinlong Jiao, Weizhen Zhuo, Mingtai Xie, D.T.Adroja, Toni Shiroka, Guochu Deng, Anmin Zhang, Feng Jin, Jianting Ji, Jie Ma, Qingming Zhang
The triangular-lattice quantum Ising antiferromagnet is a promising platform for realizing Anderson’s quantum spin liquid, though finding suitable materials to realize it remains a challenge. Here, we present a comprehensive study of NaTmSe2 using magnetization, specific heat, neutron scattering, and muon spin relaxation, combined with theoretical calculations. We demonstrate that NaTmSe2 realizes the transverse field Ising model and quantitatively determine its exchange parameters. Our results reveal a multipolar spin-polarized state coexisting with a dipolar spin-disordered state. These states feature gapless spinon excitations mediated by the multipolar moments. The study shows how multiple types of magnetism can emerge in distinct magnetic channels (dipolar and multipolar) within a single magnet, advancing our understanding of spin-frustrated Ising physics and opening pathways for different quantum computing applications.
Strongly Correlated Electrons (cond-mat.str-el), Materials Science (cond-mat.mtrl-sci)
8 pages, 4 figures
Phys. Rev. B 111, L180405 (2025) (letter)
Complex electronic topography and magnetotransport in an in-plane ferromagnetic kagome metal
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Anup Pradhan Sakhya, Richa Pokharel Madhogaria, Barun Ghosh, Nabil Atlam, Milo Sprague, Mazharul Islam Mondal, Himanshu Sheokand, Arun K. Kumay, Shirin Mozaffari, Rui Xue, Yong P. Chen, David G. Mandrus, Arun Bansil, Madhab Neupane
The intricate interplay between flat bands, Dirac cones, and magnetism in kagome materials has recently attracted significant attention from materials scientists, particularly in compounds belonging to the RMn6Sn6 family (R = Sc, Y, rare earths), due to their inherent magnetic frustration. Here, we present a detailed investigation of the ferromagnetic (FM) kagome magnet ScMn6(Sn0.78Ga0.22)6 using angle-resolved photoemission spectroscopy (ARPES), magnetotransport measurements, and density functional theory (DFT) calculations. Our findings reveal a paramagnetic-to-FM transition at 375 K, with the in-plane direction serving as the easy magnetization axis. Notably, ARPES measurements reveal a Dirac cone near the Fermi energy, while the Hall resistivity exhibits a substantial contribution from the anomalous Hall effect. Additionally, we observe a flat band spanning a substantial portion of the Brillouin zone, arising from the destructive interference of wave functions in the Mn kagome lattice. Theoretical calculations reveal that the gap in the Dirac cone can be modulated by altering the orientation of the magnetic moment. An out-of-plane orientation produces a gap of approximately 15 meV, while an in-plane alignment leads to a gapless state, as corroborated by ARPES measurements. This comprehensive analysis provides valuable insights into the electronic structure of magnetic kagome materials and paves the way for exploring novel topological phases in this material class.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
7 pages, 4 figures
Resonant and Anti-resonant Exciton-Phonon Coupling in Quantum Dot Molecules
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Michelle Lienhart, Krzysztof Gawarecki, Markus Stöcker, Frederik Bopp, Charlotte Cullip, Nadeem Akhlaq, Christopher Thalacker, Johannes Schall, Sven Rodt, Arne Ludwig, Dirk Reuter, Stephan Reitzenstein, Kai Müller, Paweł Machnikowski, Jonathan J. Finley
Optically active quantum dot molecules (QDMs) can host multi-spin quantum states with the potential for the deterministic generation of photonic graph states with tailored entanglement structures. Their usefulness for the generation of such non-classical states of light is determined by orbital and spin decoherence mechanisms, particularly phonon-mediated processes dominant at energy scales up to a few millielectronvolts. Here, we directly measure the spectral function of orbital phonon relaxation in a QDM and benchmark our findings against microscopic kp theory. Our results reveal phonon-mediated relaxation rates exhibiting pronounced resonances and anti-resonances, with rates ranging from several ten ns$ ^{-1}$ to tens of $ \mu$ s$ ^{-1}$ . Comparison with a kinetic model reveals the voltage (energy) dependent phonon coupling strength and fully explains the interplay between phonon-assisted relaxation and radiative recombination. These anti-resonances can be leveraged to increase the lifetime of energetically unfavorable charge configurations needed for realizing efficient spin-photon interfaces and multi-dimensional cluster states.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Hidden Bose-Einstein Singularities in Correlated Electron Systems: II. Pseudogap Phase in the Weakly Attractive Hubbard Model
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
The hidden Bose-Einstein singularities of correlated electron systems, whose possible existence has been pointed out in a previous paper based on quantum field theory of ordered phases [T. Kita, J. Phys. Soc. Jpn. {\bf 93}, 124704 (2024)], are studied in more detail in terms of the attractive Hubbard model, for which the mean-field theory predicts that spin-singlet superconductivity is realized at low enough temperatures for any band structure and interaction strength. It is shown that incorporating correlation effects should change the mean-field superconducting solution substantially and qualitatively even in the weak coupling, implying that the system lies in the strong-coupling region perturbatively. The hidden singularity is found to be present around the mean-field superconducting temperature $ T_{ {\rm c}0}$ , below which the standard self-consistent treatment by quantum field theory cannot be used due to divergences in the zero Matsubara frequency branch obeying Bose-Einstein statistics. Our method to recover the applicability with a Lagrange multiplier predicts that the singularity is a physical entity signaling the threshold of a pseudogap phase with a characteristic V-shape structure in the density of states near zero energy, which lies above the superconducting phase and originates from the emerging one-particle-reducible structure in the self-energy.
Strongly Correlated Electrons (cond-mat.str-el), Quantum Gases (cond-mat.quant-gas), Statistical Mechanics (cond-mat.stat-mech), Superconductivity (cond-mat.supr-con)
11 pages, 5 figures
Local variations of the magnetization effected by an external field in molecular rings
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
It is shown that an external magnetic field generates local variations of the classical ground-state magnetization in molecular rings of antiferromagnetic icosahedra with isotropic spin interactions. The magnetic response is characterized by a multitude of magnetization discontinuities occurring across the ring. In addition, a parity effect with respect to the number of icosahedra allows for magnetization jumps that occur at different field values for different molecules and produce an even more pronounced local variation of the magnetization. It is also found that for specific field ranges all canting angles of the molecular magnetizations increase with the field. These findings are in sharp contrast with the ones for rings of individual spins.
Strongly Correlated Electrons (cond-mat.str-el)
8 pages, 16 figures, 2 tables
Coupling between magnetism and band structure in a 2D semiconductor
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Lihuan Sun, Marco Gibertini, Alessandro Scarfato, Menghan Liao, Fan Wu, Alberto F. Morpurgo, Christoph Renner
Van der Waals semiconducting magnets exhibit a cornucopia of physical phenomena originating from the interplay of their semiconducting and magnetic properties. However, a comprehensive understanding of how semiconducting processes and magnetism are coupled is lacking. We address this question by performing scanning tunneling spectroscopy (STS) measurements on the magnetic semiconductor CrPS$ _4$ , and by comparing the results to photoluminescence experiments and density functional theory (DFT) calculations. Below the magnetic transition, STS exhibit multiple features absent in the paramagnetic state, caused by the proliferation of electronic bands due to spin splitting with a large ($ \simeq 0.5$ eV) exchange energy. The energetic differences between the band edges determined by STS match all observed photoluminescence transitions, which also proliferate in the magnetic state. DFT calculations quantitatively predict the relative positions of all detected bands, explain which pairs of bands lead to radiative transitions, and also reproduce the measured spatial dependence of electronic wavefunctions. Our results reveal how all basic optoelectronic processes observed in CrPS$ _4$ can be understood in terms of the evolution of the electronic band structure when entering the magnetic state, and allow us to conclude that individual bands are fully spin-polarized over a broad energy interval.
Materials Science (cond-mat.mtrl-sci)
Ultrafast excitation of polar skyrons
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Huaiyu (Hugo)Wang, Vladimir Stoica, Cheng Dai, Marek Paściak, Sujit Das, Tiannan Yang, Mauro A. P. Gonçalves, Jiri Kulda, Margaret R. McCarter, Anudeep Mangu, Yue Cao, Hari Padma, Utkarsh Saha, Diling Zhu, Takahiro Sato, Sanghoon Song, Mathias Hoffmann, Patrick Kramer, Silke Nelson, Yanwen Sun, Quynh Nguyen, Zhan Zhang, Ramamoorthy Ramesh, Lane Martin, Aaron M. Lindenberg, Long-Qing Chen, John W. Freeland, Jirka Hlinka, Venkatraman Gopalan, Haidan Wen
Unraveling collective modes arising from coupled degrees of freedom is crucial for understanding complex interactions in solids and developing new functionalities. Unique collective behaviors emerge when two degrees of freedom, ordered on distinct length scales, interact. Polar skyrmions, three-dimensional electric polarization textures in ferroelectric superlattices, disrupt the lattice continuity at the nanometer scale with nontrivial topology, leading to previously unexplored collective modes. Here, using terahertz-field excitation and femtosecond x-ray diffraction, we discovered subterahertz collective modes, dubbed ‘skyrons’, which appear as swirling patterns of atomic displacements functioning as atomic-scale gearsets. Momentum-resolved time-domain measurements of diffuse scattering revealed an avoided crossing in the dispersion relation of skyrons. We further demonstrated that the amplitude and dispersion of skyrons can be controlled by sample temperature and electric-field bias. Atomistic simulations and dynamical phase-field modeling provided microscopic insights into the three-dimensional crystallographic and polarization dynamics. The discovery of skyrons and their coupling with terahertz fields opens avenues for ultrafast control of topological polar structures.
Materials Science (cond-mat.mtrl-sci), Applied Physics (physics.app-ph)
Theoretical investigations of electronic and optical properties of double perovskite Cs$_2$Tl$BX_6$ ($B=$ Bi, In; $X=$ Cl, Br, I) for photovoltaic application
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Lead-free double perovskites are gaining attention for photovoltaic (PV) applications due to their long carrier lifetimes, tunable bandgaps, and low toxicity. Using first-principles calculations, we studied the structural, electronic and optical properties of Cs$ _2$ Tl$ BX_6$ ($ B=$ Bi, In; $ X=$ Cl, Br, I). The cubic phase (space group Fm3m) was analyzed within the projector-augmented wave (PAW) method. Our calculations predict direct bandgaps of 1.9-1.2 eV for Cs$ _2$ TlBi$ X_6$ and indirect bandgaps of 2.4–0.8 eV for Cs$ _2$ TlIn$ X_6$ . Notably, the bandgap energy decreases with anion substitution from Cl to I, making these materials highly active in the near-infrared to visible light range. We reveal that Cs$ _2$ TlBi$ X_6$ exhibits the highest optical absorption, with a peak value of $ 5\times10^5$ cm$ ^{-1}$ at an incident photon energy of 3 eV. Additionally, we evaluated the transport properties using the Boltzmann transport equations. The results indicate that Cs$ _2$ TlBi$ X_6$ exhibit high electrical conductivity, reaching $ 8\times10^6$ S/m, and high electron mobility of 120 cm$ ^2/$ V.s. PV performance analysis further reveals promising power conversion efficiencies (PCE) of up to 42%, with Cs$ _2$ TlBi$ X_6$ showing significantly higher PCE than Cs$ _2$ TlIn$ X_6$ . These reports highlight the potential of Cs$ _2$ TlBi$ X_6$ for advanced photovoltaic devices.
Materials Science (cond-mat.mtrl-sci)
13 pages, 9 figures
Microwave resonator for measuring time-reversal symmetry breaking at cryogenic temperatures
New Submission | Superconductivity (cond-mat.supr-con) | 2025-05-16 20:00 EDT
We present a microwave-frequency method for measuring polar Kerr effect and spontaneous time-reversal symmetry breaking (TRSB) in unconventional superconductors. While this experiment is motivated by work performed in the near infrared using zero-loop-area Sagnac interferometers, the microwave implementation is quite different, and is based on the doubly degenerate modes of a TE$ _{111}$ cavity resonator, which act as polarization states analogous to those of light. The resonator system has in-situ actuators that allow quadrupolar distortions of the resonator shape to be controllably tuned, as these compete with the much smaller perturbations that arise from TRSB. The most reliable way to the detect the TRSB signal is by interrogating the two-mode resonator system with circularly polarized microwaves, in which case the presence of TRSB shows up unambiguously as a difference between the forward and reverse transmission response of the resonator - i.e., as a breaking of reciprocity. We illustrate and characterize a coupler system that generates and detects circularly polarized microwaves, and then show how these are integrated with the TE$ _{111}$ resonator, resulting in a dilution refrigerator implementation with a base temperature of 20 mK. We show test data on yttrium-iron-garnet (YIG) ferrite as an illustration of how the system operates, then present data showing system performance under realistic conditions at millikelvin temperatures.
Superconductivity (cond-mat.supr-con)
9 pages, 12 figures
Enhanced coercive force of nanoparticles of special morphology in the Stoner-Wohlfarth model
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Vladimir P. Savin, Yury A. Koksharov
We have found an unusual effect of increasing the coercive force in the Stoner-Wohlfarth model applied to magnetic nanoparticles of a special morphology. The particles consist of a ferromagnetic single-domain core surrounding by a magnetically soft shell. We have studied thoroughly individual and collective properties of these particles both through numerical calculations and analytical analysis. Fairly accurate approximate analytical formulas have been obtained for determining magnetization, hysteresis loop, coercive force, and other magnetic properties of the particles. The physical reason of the coercivity enhancement effect is the magnetic screening of a particle core by its shell. We have found the unambiguous conditions necessary for the existence of this effect. The large magnetization and moderate magnetic anisotropy of the core favor the effect of the coercivity enhancement.
Materials Science (cond-mat.mtrl-sci)
22 pages, 11 figures
QR$^2$-code: An open-source program for double resonance Raman spectra
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Jianqi Huang, Renhui Liu, Ye Zhang, Nguyen Tuan Hung, Huaihong Guo, Riichiro Saito, Teng Yang
We present an open-source program, QR$ ^2$ -code, that computes double-resonance Raman (DRR) spectra using first-principles calculations. QR$ ^2$ -code can calculate not only two-phonon DRR spectra but also single-resonance Raman spectra and defect-induced DRR spectra. For defect-induced DDR spectra, we simply assume that the electron-defect matrix element of elastic scattering is a constant. Hands-on tutorials for graphene are given to show how to run QR$ ^2$ -code for single-resonance, double-resonance, and defect-induced Raman spectra. We also compare the single-resonance Raman spectra by QR$ ^2$ -code with that by QERaman code. In QR$ ^2$ -code, the energy dispersions of electron and phonon are taken from Quantum ESPRESSO (QE) code, and the electron-phonon matrix element is obtained from the electron-phonon Wannier (EPW) code. All codes, examples, and scripts are available on the GitHub repository.
Materials Science (cond-mat.mtrl-sci), Optics (physics.optics)
13 pages, 5 figures, 2 tables
Electron spin resonance with scanning tunneling microscopy: a tool for an on-surface quantum platform of identical qubits
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Deung-Jang Choi, Soo-hyon Phark, Andreas J. Heinrich, Nicolás Lorente
Integration of electron spin resonance (ESR) in a scanning tunneling microscope (STM) has enabled an all-electrical control of atomic and molecular spins on solid surfaces with atomic-scale precision and energy resolution beyond thermal limitations. Further, coherent manipulation and detection of individual spins in an ESR-STM establishes a powerful quantum platform, allowing for the implementation of fundamental quantum logic operations to on-surface identical qubits. In this review, we introduce recent advances of ESR-STM, focusing on its application to atomic-scale qubits and extension to molecular qubit systems. We discuss the principles underlying ESR-STM, followed by single-spin addressability, coherent control via Rabi oscillations, and quantum state readout through frequency-resolved detection. We further demonstrate multi-qubit control architectures enabled by atom manipulation and local magnetic field engineering, culminating in the realization of multi-qubit logic gates such as the Controlled-NOT and Toffoli gates. These implementations highlight the specialty of ESR-STM towards atomic-scale quantum circuits. Indeed, ESR-STM can be an excellent tool to perform and evaluate quantum operations in molecular qubits. The results reviewed in this collection establish ESR-STM as a versatile tool for advancing quantum coherent science at the atomic and molecular level in solid-state environments.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Quantum Physics (quant-ph)
Accelerated snapping of slender beams under lateral forcing
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-05-16 20:00 EDT
Colin M. Meulblok, Hadrien Bense, M. Caelen, Martin van Hecke
The hysteretic snapping under lateral forcing of a compressed, buckled beam is fundamental for many devices and mechanical metamaterials. For a single-tip lateral pusher, an important limitation is that snapping requires the pusher to cross the centerline of the beam. Here, we show that dual-tip pushers allow accelerated snapping, where the beam snaps before the pusher reaches the centerline. As a consequence, we show that when a buckled beam under increased compression comes in contact with a dual-tip pusher, it can snap to the opposite direction – this is impossible with a single-tip pusher. Additionally, we reveal a novel two-step snapping regime, in which the beam sequentially loses contact with the two tips of the dual-tip pusher. To characterize this class of snapping instabilities, we employ a systematic modal expansion of the beam shape. This expansion allows us to capture and analyze the transition from one-step to two-step snapping geometrically. Finally we demonstrate how to maximize the distance between the pusher and the beam’s centerline at the moment of snapping. Together, our work opens up a new avenue for quantitatively and qualitatively controlling and modifying the snapping of buckled beams, with potential applications in mechanical sensors, actuators, and metamaterials.
Soft Condensed Matter (cond-mat.soft)
10 pages, 8 figures
Floquet topological phases of higher winding numbers in extended Su-Schrieffer-Heeger model under quenched drive
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Rittwik Chatterjee, Asim Kumar Ghosh
In this study topological properties of static and dynamic
Su-Schrieffer-Heeger models with staggered further neighbor hopping terms
of different extents are investigated. Topological characterization
of the static chiral models is established in terms of
conventional winding number while Floquet topological character is
studied by a pair of winding numbers.
With the increase of extent of further neighbor terms topological phases
with higher winding numbers are found to emerge in both static and dynamic
systems. Topological phase diagrams of static models for four different
extents of further neighbor terms are presented, which has been generalized
for arbitrary extent afterwards. Similarly, Floquet topological
phase diagrams of four such dynamic models have been presented.
For every model four different parametrizations of hopping terms
are introduced which
exhibits different patterns of topological phase diagrams.
In each case emergence of 0' and $ \pi$ ‘ energy edge states
is noted and they are found to consistent to the
bulk-boundary correspondence rule applicable for chiral topological systems.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
12 pages and 13 figures
Quantum criticality and non-Fermi liquids: the nonperturbative renormalization group perspective
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
Mateusz Homenda, Pawel Jakubczyk, Hiroyuki Yamase
We develop a thorough theoretical framework based on the nonperturvative renormalization group (RG) a la Wetterich to tackle the interplay of coupled fermionic and order-parameter fluctuations at metallic quantum critical points with ordering wavevectors $ \vec{Q}=\vec{0}$ . We consistently treat the dynamical emergence of the Landau damping of the bosonic mode and non-Fermi liquid scaling of fermions upon lowering the cutoff scale. The loop integrals of the present theory involve only contributions from fluctuations above the cutoff scale, which drive the system to a non-Fermi liquid RG fixed point of different scaling properties from those obtained within the random phase approximation (RPA) or expansions around it. In particular the scaling exponent for the Fermi self-energy acquires the value $ \alpha\approx 0.50$ rather than the anticipated $ \alpha\approx 0.66$ , while the bosonic dynamical exponent $ z\approx 2$ . We demonstrate how results characteristic for the RPA-type fixed-point scaling are recovered in our framework by a questionable procedure of removing the fermionic cutoff much faster than the bosonic one.
Strongly Correlated Electrons (cond-mat.str-el), High Energy Physics - Theory (hep-th)
Cavity-Mediated Electron-Electron Interactions: Renormalizing Dirac States in Graphene
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Hang Liu, Francesco Troisi, Hannes Hübener, Simone Latini, Angel Rubio
Embedding materials in optical cavities has emerged as a strategy for tuning material properties. Accurate simulations of electrons in materials interacting with quantum photon fluctuations of a cavity are crucial for understanding and predicting cavity-induced phenomena. In this article, we develop a non-perturbative quantum electrodynamical approach based on a photon-free self-consistent Hartree-Fock framework to model the coupling between electrons and cavity photons in crystalline materials. We apply this theoretical approach to investigate graphene coupled to the vacuum field fluctuations of cavity photon modes with different types of polarizations. The cavity photons introduce nonlocal electron-electron interactions, originating from the quantum nature of light, that lead to significant renormalization of the Dirac bands. In contrast to the case of graphene coupled to a classical circularly polarized light field, where a topological Dirac gap emerges, the nonlocal interactions induced by a quantum linearly polarized photon mode give rise to the formation of flat bands and the opening of a topologically trivial Dirac gap. When two symmetric cavity photon modes are introduced, Dirac cones remain gapless, but a Fermi velocity renormalization yet indicates the relevant role of nonlocal interactions. These effects disappear in the classical limit for coherent photon modes. This new self-consistent theoretical framework paves the way for the simulation of non-perturbative quantum effects in strongly coupled light-matter systems, and allows for a more comprehensive discovery of novel cavity-induced quantum phenomena.
Materials Science (cond-mat.mtrl-sci), Optics (physics.optics), Quantum Physics (quant-ph)
20 pages, 10 figures
Unconventional superconductivity of an altermagnetic metal: Polarized BCS and inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov states
New Submission | Superconductivity (cond-mat.supr-con) | 2025-05-16 20:00 EDT
We investigate the superconductivity of two-dimensional spin-1/2 Fermi systems with $ d$ -wave altermagnetism under external magnetic field near zero temperature. At large altermagnetic coupling without magnetic field, we show that altermagnetism drives a second-order phase transition from the standard Bardeen-Cooper-Schrieffer (BCS) state to an inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The inclusion of magnetic field turns the BCS state into a long-sought polarized BCS superconductor with spin-population imbalance. It also shrinks the parameter window of the FFLO state and eventually leads to a nontrivial quantum tri-critical Lifshitz point, where two second-order phase transition lines between the polarized BCS, FFLO and normal states intersect. At small altermagnetic coupling, we find the usual route to the FFLO state driven by magnetic field. The presence of the altermagnetic coupling narrows the phase window of the FFLO state and creates another quantum Lifshitz point, where a first-order transition curve meets a second-order transition line. Between the two Lifshitz points, the transition from the polarized BCS state to the normal state is smooth. Our predicted rich phase diagram is relevant to some recently discovered unconventional magnets, including RuO$ _{2}$ that exhibits a relatively high superconducting temperature in the thin film limit under applied strain. Our results of unconventional superfluidity are also testable in ultracold atom laboratories, where a spin-1/2 altermagnetic Fermi gas might be realizable upon loading into two-dimensional Hubbard lattices.
Superconductivity (cond-mat.supr-con), Quantum Gases (cond-mat.quant-gas), Strongly Correlated Electrons (cond-mat.str-el)
10 pages, 8 figures
Alkali Intercalation of Moire Heterostructures for Low-Loss Plasmonics
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Ali Ghorashi, Nicholas Rivera, Ravishankar Sundararaman, Efthimios Kaxiras, John Joannopoulos, Marin Soljačić
Two-dimensional metals generically support gapless plasmons with wavelengths well below the wavelength of free-space radiation at the same frequency. Typically, however, this substantial confinement of electromagnetic energy is associated with commensurately high losses, and mitigating such losses may only be achieved through judicious band structure engineering near the Fermi level. In a clean system, an isolated, moderately flat, band at the Fermi level with sufficiently high carrier density can support a plasmon that is immune to propagation losses up to some order in the electron-phonon interaction. However, proposed materials that satisfy these criteria have been ferromagnetic, structurally unstable, or otherwise difficult to fabricate. Here, we propose a class of band structure engineered materials that evade these typical pitfalls – Moire heterostructures of hexagonal boron nitride intercalated with alkali atoms. We find that only sodium atoms engender a sufficiently isolated band with plasmons lossless at first order in the electron-phonon interaction. We calculate higher order electron-phonon losses and find that at frequencies of about $ 1$ eV the electron-phonon decay mechanism is negligible – leading to a contribution to the decay rate of about 10^7 Hz in a small frequency range. We next calculate losses from the electron-electron interaction and find that this is the dominant process – leading plasmons to decay to lower frequency plasmons at a rate of around 10^14 Hz.
Materials Science (cond-mat.mtrl-sci)
Giant spin-to-charge conversion in germanium tin epilayers
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
S. Oyarzún, C. Gonzalez-Fuentes, Erick Burgos, M. Myronov, M. Jamet, R. L.Rodríguez-Suárez, F. Pezzoli
We report a study of the spin-to-charge current conversion in compressively strained Ge1-xSnx alloy epilayers as a function of the Sn concentration by means of the inverse spin Hall effect (ISHE). The spin current is generated by spin-pumping effect (SPE) from a thin NiFe layer driven into ferromagnetic resonance (FMR). By simultaneously measuring the magnetic damping of the NiFe layer and the ISHE-induced charge current we extract two key spintronics parameters: the spin Hall angle and the effective spin mixing conductance. Our results reveal a giant spin-to-charge conversion and a non-monotonic dependence of the charge current signal on the Sn concentration, consistent with the variation in the magnetic damping observed in FMR. The values of spin Hall angle are comparable to those reported for heavy metals such as Pt and Ta. Furthermore, we show that the spin conductivity at the Au/GeSn interface can be enhanced by tuning the Sn concentration.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
15 pages, 4 figures
Quantum Lifshitz points in an altermagnetic metal
New Submission | Superconductivity (cond-mat.supr-con) | 2025-05-16 20:00 EDT
We predict the existence of two tri-critical quantum Lifshitz points in recently discovered $ d$ -wave altermagnetic metals subjected to an external magnetic field. These points connect a spatially modulated Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase, a uniform polarized Bardeen–Cooper–Schrieffer (BCS) superconducting phase, and the normal metallic phase in a nontrivial manner. Depending on whether the FFLO state is primarily induced by the magnetic field or by $ d$ -wave altermagnetism, we classify the corresponding Lifshitz points as field-driven or altermagnetism-driven, respectively. Notably, the two types exhibit distinct behaviors: the transition from the FFLO phase to the polarized BCS phase is first-order near the field-driven Lifshitz point, as might be expected, whereas it becomes continuous near the altermagnetism-driven Lifshitz point. We further explore the effects of finite temperature and find that the altermagnetism-driven Lifshitz point is significantly more sensitive to thermal fluctuations.
Superconductivity (cond-mat.supr-con), Quantum Gases (cond-mat.quant-gas), Statistical Mechanics (cond-mat.stat-mech), Strongly Correlated Electrons (cond-mat.str-el), Quantum Physics (quant-ph)
6 pages, 4 figures
Generalized Non-Hermitian Skin Effect
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Zheng Wei, Ji-Yao Fan, Kui Cao, Xin-Ran Ma, Su-Peng Kou
In this Letter, we present a unified theory termed the generalized non-Hermitian skin effect. This framework provides a universal characterization of typical one-dimensional non-Hermitian skin effects within the perturbative regime and unveils a novel type of skin effect that beyond the predictions of the generalized Brillouin zone theory, referred to as the relative skin effect. Previously recognized skin effects are classified as global skin effects, thereby explicitly delineating the scope and limitations of existing non-Bloch band theories. Additionally, we establish, for the first time, a phase transition criterion between global skin effects and relative skin effect, demonstrating the competition between these two distinct types of skin effects, emphasizing the pivotal role of real-space non-Hermitian terms in understanding skin effects and challenging the traditional reliance of non-Bloch band theory on momentum space. Our study substantially advances the conceptual framework of non-Hermitian physics and provides new theoretical tools for investigation.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Inferring activity from the flow field around active colloidal particles using deep learning
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-05-16 20:00 EDT
Aditya Mohapatra, Aditya Kumar, Mayurakshi Deb, Siddharth Dhomkar, Rajesh Singh
Active colloidal particles create flow around them due to non-equilibrium process on their surfaces. In this paper, we infer the activity of such colloidal particles from the flow field created by them via deep learning. We first explain our method for one active particle, inferring the $ 2s$ mode (or the stresslet) and the $ 3t$ mode (or the source dipole) from the flow field data, along with the position and orientation of the particle. We then apply the method to a system of many active particles. We find excellent agreements between the predictions and the true values of activity. Our method presents a principled way to predict arbitrary activity from the flow field created by active particles.
Soft Condensed Matter (cond-mat.soft), Fluid Dynamics (physics.flu-dyn)
10 pages, 4 Figures, and 1 Algorithm
Chiral near-field control of quantum light generation using magneto-optical graphene
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Mikkel Have Eriksen, Joel D. Cox
We theoretically explore strategies to actively control photon emission from quantum light sources by leveraging the large magneto-optical response of graphene. The quantum electrodynamic response of graphene – characterized by the Purcell factor and the Lamb shift of a proximal emitter – is analyzed for extended two-dimensional sheets, one-dimensional nanoribbons, and zero-dimensional nanodisks, all of which are endowed with an intrinsic chiral near-field response under a static perpendicular magnetic field. Using rigorous semianalytical models of these systems, we reveal that the emission properties can be readily tuned by variations in doping charge carrier density and applied magnetic field strength, both with respect to magnetoplasmon resonances (at infrared frequencies) and Shubnikov-de-Haas oscillations (entering telecommunication bands) associated with optical transitions between discrete Landau levels. Localized magnetoplasmons in graphene nanoribbons are predicted to induce large dissymmetry in the spontaneous emission from left-hand and right-hand circularly polarized transitions in a proximal quantum emitter, presenting applications for chiral quantum optical waveguiding. This chiral dissymmetry is further enhanced in gyrotropic graphene nanodisks, signaling that the spatial shaping of near-fields in nanostructured graphene can significantly boost the intrinsic chiral response induced by the magnetic field. These results indicate that magneto-optical graphene constitutes a versatile and highly tunable platform for quantum light generation and manipulation at the nanoscale.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Optics (physics.optics)
16 pages, 4 figures
High frequency permeability of the composite with ferromagnetic spherical shells
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
The paper studies high-frequency permeability of the composite materials consisting of hollow ferromagnetic particles embedded into the non-magnetic media. We model the ferromagnetic particles in composite by spherical shell: the thickness of the ferromagnetic region $ d$ compared to the particles’ diameter $ D$ can vary in a wide range, from $ d\ll D$ to $ d\sim D$ . We assume that the magnetization distribution in such a particle is non-uniform, but forms a vortex-like structure: the magnetization is twisted in some plain outside two vortex cores placed at the poles of the particle. The high-frequency permeability of such a composite material has been studied in the limit of non-interacting particles. We study the dependence of the permeability on the ratio $ d/D$ . It was shown, in particular, that in the limit $ d/D\ll1$ the frequency dependence of the particle’s susceptibility is quite similar to that for the thin film. At the same time, the magnetization oscillations in the ac field are non-homogeneous.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
12 pages, 7 figures
Sensing a magnetic rare-earth surface alloy by proximity effect with an open-shell nanographene
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Nicolò Bassi (1), Jan Wilhelm (2,3), Nils Krane (1), Feifei Xiang (1), Patrícia Čmelová (4), Elia Turco (1), Pierluigi Gargiani (5), Carlo Pignedoli (1), Michal Juríček (4), Roman Fasel (1,6), Richard Koryt ár (7), Pascal Ruffieux (1). ((1) EMPA Switzerland, (2) Regensburg Center for Ultrafast Nanoscopy Germany, (3) Institute of Theoretical Physics Germany, (4) Department of Chemistry Switzerland, (5) ALBA Synchrotron Light Source Spain, (6) Department of Chemistry, Biochemistry and Pharmaceutical Sciences University of Bern Switzerland (7) Department of Condensed Matter Physics Charles University Czech Republic)
Open-shell nanographenes have attracted significant attention due to their structurally tunable spin ground state. While most characterization has been conducted on weakly-interacting substrates such as noble metals, the influence of magnetic surfaces remains largely unexplored. In this study, we investigate how TbAu2, a rare-earth-element-based surface alloy, affects the magnetic properties of phenalenyl (or [2]triangulene (2T)), the smallest spin-1/2 nanographene. Scanning tunneling spectroscopy (STS) measurements reveal a striking contrast: while 2T on Au(111) exhibits a zero-bias Kondo resonance - a hallmark of a spin-1/2 impurity screened by the conduction electrons of the underlying metal - deposition on TbAu2 induces a symmetric splitting of this feature by approximately 20 mV. We attribute this splitting to a strong proximity-induced interaction with the ferromagnetic out-of-plane magnetization of TbAu2. Moreover, our combined experimental and first-principles analysis demonstrates that this interaction is spatially modulated, following the periodicity of the TbAu2 surface superstructure. These findings highlight that TbAu2 serves as a viable platform for stabilizing and probing the magnetic properties of spin-1/2 nanographenes, opening new avenues for the integration of {\pi}-magnetic materials with magnetic substrates.
Materials Science (cond-mat.mtrl-sci), Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Floquet engineering triplet superconductivity in superconductors with spin-orbit coupling or altermagnetism
New Submission | Superconductivity (cond-mat.supr-con) | 2025-05-16 20:00 EDT
We study superconductivitiy under light irradiation based on the Floquet-Magnus expansion in the high-frequency regime. We find that, in spin-singlet superconductors with spin-orbit coupling, triplet superconductivity can be induced in the first-order perturbation for dynamical gap functions and the second-order perturbation for static gap functions. We also show that, in unitary triplet superconductors with altermagnetism, nonunitary triplet superconductivity can emerge in the firstorder perturbation for dynamical gap function and in the second-order perturbation for static gap functions. These results indicate optical generation and control of triplet superconductivity.
Superconductivity (cond-mat.supr-con)
11 pages, 2 figures
Topological properties of domain walls in antiferromagnetic topological insulators
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Gabriele Naselli, Ion Cosma Fulga
Motivated by the study of stacking faults in weak topological insulators and the observation of magnetic domain walls in MnBi$ _{2n}$ Te$ _{3n+1}$ , we explore the topological properties of domain walls in antiferromagnetic topological insulators. We develop two tight-binding models: one based on a strong topological insulator with antiferromagnetic order, and another built from stacked Chern insulators with alternating Chern numbers. Both systems are dual topological insulators, i.e. they are at the same time antiferromagnetic and crystalline topological insulators, but differ by the type of mirror symmetry protecting the crystalline phase: spinful versus spinless. We show that in the spinful case the mirror Chern number is invariant under time reversal and that it changes sign in the spinless case. This influences the properties of the two systems in the presence of a magnetic domain wall, which is created in the system when the magnetization is flipped via a time-reversal transformation. In the first type, the bulk of the domain wall is gapped but the defect will host chiral edge states when it ends on an external ferromagnetic surface. In the second, due to the flip in the mirror Chern number, the domain wall is a two-dimensional embedded semimetal with 2D gapless states protected by mirror symmetry. Our results show that domain walls can be a source of non-trivial topology, allowing to generate and manipulate gapless states within the bulk and the ferromagnetic surfaces of antiferromagnetic topological insulators.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Spin-orbit physics stemming from mixed parity superconductivity: A relationship between mixed parity superconductivity and magnetism with spin-orbit coupling
New Submission | Superconductivity (cond-mat.supr-con) | 2025-05-16 20:00 EDT
We show that Hamiltonian for mixed parity superconductivity can be recast into that for magnetism with spin-orbit coupling by the Schrieffer-Wolff transformation, indicating that mixed parity superconductivity and magnetism with spin-orbit coupling can share the same physics. As demonstrations, we discuss the Dzyaloshinskii-Moriya type interactions, magnetoelectric effect, supercurrent-induced spin current, and altermagnetism in mixed parity superconductors. All these effects originate purely from mixed parity superconductivity.
Superconductivity (cond-mat.supr-con)
6 pages
Tuning the morphology of aerosolised cellulose nanocrystals via controlled aggregation
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-05-16 20:00 EDT
Daniel Warnes, Jia Hui Lim, Richard M. Parker, Bruno Frka-Petesic, Ray Freshwater, Camila Honorato-Rios, Yu Ogawa, Chiara Giorio, Silvia Vignolini
Cellulose nanocrystals (CNCs) are polycrystalline, rod-shaped nanoparticles isolated from cellulose, which have attracted increasing attention for a wide variety of applications. While there has been significant research into CNCs in suspensions, hydrogels and films, there have been remarkably few studies that investigated their properties during and after aerosolisation. Here, we studied how aerosolisation impacts the size and morphology of different CNCs suspensions with different surface functionalities. By building a new experimental setup, we observed that colloidally-metastable aqueous CNC suspensions, achieved by carboxylation of the surface hydroxy groups or by exposure to high intensity ultrasonication, yield large particulates upon aerosolisation under ambient temperatures. In contrast, aqueous suspensions of unfunctionalised CNCs tend to produce, upon aerosolisation, smaller particulates, despite suffering from poor colloidal stability in liquid suspension. Our results demonstrate that both the aerosolisation process itself and the properties of the CNC suspension play a crucial role in determining the final particle size and morphology of CNC-based particles, highlighting the need to consider colloidal stability and surface functionality when designing CNC-based materials for applications involving aerosol delivery or spray drying.
Soft Condensed Matter (cond-mat.soft)
24 pages, 5 figures
Phonon Edelstein effect in chiral metals
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
We propose a mechanism of current-induced phonon angular momentum, which we call phonon Edelstein effect. We investigate this effect in three-dimensional chiral metals with spin-orbit coupling and chiral phonons, and obtain an analytical expression of phonon angular momentum induced by the current. We also discuss the physical interpretation of this effect and give an estimation of its magnitude.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
6 pages, 2 figures
First-Principles Calculation of Spin-Relaxation Due to Alloy and Electron-Phonon Scattering in Strained GeSn
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Kevin Sewell, Felipe Murphy-Armando
GeSn has emerged as a promising material for spintronics due to its long spin-lifetime, compatibility with silicon technology, high mobility and tunable electronic properties. Of particular interest is the transition from an indirect to a direct band gap with increasing Sn content, which enhances optical properties, electron transport and we find also affects spin transport behaviour, which is critical for spintronics applications. We use first-principles electronic-structure theory to determine the spin-flip electron-alloy scattering parameters in n-type GeSn alloys. We also calculate the previously undetermined intervalley electron spin-phonon scattering parameters between the $ L$ and $ \Gamma$ valleys. These parameters are used to determine the electron-alloy and electron-phonon scattering contributions to the n-type spin-relaxation of GeSn, as a function of alloy content and temperature. As in the case of phonon scattering, alloy scattering reduces the spin-relaxation time. However, switching the spin transport from the typical $ L$ valley of Ge to the $ \Gamma$ valley by sufficient addition of Sn, the relaxation time can be substantially increased. For unstrained, room temperature GeSn, we find a Sn concentration of at least $ 10%$ is required to achieve a spin-relaxation time greater than Ge, with $ 17%$ Sn needed to increase the spin-relaxation time from the nanosecond range to the microsecond range. At low temperatures (30K), adding $ 10%$ Sn can increase the spin-relaxation time from $ 10^{-7}$ s to 0.1s. Applying biaxial tensile strain to GeSn further increases the spin-relaxation time and at a lower Sn content than in unstrained GeSn.
Materials Science (cond-mat.mtrl-sci)
Magnetic correlations and superconducting pairing near higher-order Van Hove singularities
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
Zheng Wei, Yanmei Cai, Boyang Wen, Tianxing Ma
We explore magnetic correlations and superconducting pairing near higher-order Van Hove singularities in an extended Hubbard model on honecycomb lattice incorporating third-nearest-neighbor hopping ( t’’ ). Using quantum Monte Carlo methods, we identify a crossover between ferromagnetic and antiferromagnetic fluctuations near higher-order Van Hove singularities filling, where ( t’’ ) enhances ferromagnetic correlations below while suppressing antiferromagnetic fluctuations toward half-filling. At low doping, ( f_n )-wave pairing dominates, amplified by higher-order Van Hove singularities-induced divergent density of states. Remarkably, despite general suppression of ( f_n )-wave pairing by increasing next-nearest neighbor hopping ( t’ ) and ( t’’ ), a critical ( t’’ = 0.15 ) triggers anomalous enhancement via higher-order Van Hove singularities renormalization at a fix $ t’$ . The nearest-neighbor Coulomb interactions ( V ) suppress superconducting correlation, which exhibiting sign-independent suppression proportional to ( |V| ). These results highlight the interplay of higher-order Van Hove singularities-driven electronic structure, magnetic fluctuations, and pairing symmetry competition in electron correlated systems.
Strongly Correlated Electrons (cond-mat.str-el), Superconductivity (cond-mat.supr-con)
6 pages, 7 figures
Deciphering the role of LiBr as redox mediator in Li-O2 Aprotic Batteries
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Angelica Petrongari, Lucrezia Desiderio, Adriano Pierini, Enrico Bodo, Mauro Giustini, Sergio Brutti
Lithium-oxygen batteries are among the most promising energy storage systems due to their high theoretical energy density, but their practical implementation is hindered by poor reversibility and parasitic reactions. Redox mediators such as LiBr have emerged as a strategy to enhance reaction kinetics and reduce overpotentials. In this study, we explore the impact of three different solvents, dimethoxyethane (DME), tetraethylene glycol dimethyl ether (TEGDME), and dimethyl sulfoxide (DMSO), on the electrochemical performance and reaction pathways of LiBr-mediated Li-O2 cells. Our results reveal that a 1O2 evolution channel that leads to singlet oxygen-induced cell degradation is active only in the TEGDME-based electrolyte. Both DME and DMSO allow singlet oxygen-free Oxygen Evolution Reaction, but only DME is found chemically stable in the LiBr-mediated Li-O2 cell working conditions. These findings highlight the critical role of solvent-mediator interactions in determining the performance of Li-O2 cells.
Materials Science (cond-mat.mtrl-sci), Chemical Physics (physics.chem-ph)
Thermodynamic Variational Principle Unifying Gravity and Heat Flow
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-05-16 20:00 EDT
Naoko Nakagawa, Shin-ichi Sasa
Predicting the stable phase configuration in a liquid-gas system becomes a fundamental challenge when the stratification favored by gravity conflicts with arrangements induced by heat flow, particularly because standard equilibrium thermodynamics is insufficient in such non-equilibrium steady states. We propose a variational principle based on an extended thermodynamics, called global thermodynamics, to address this state selection problem. Our key finding is that gravity and heat flow effects are unified into a single parameter, ``effective gravity’’ ($ g_\mathrm{eff}$ ), within this framework. Crucially, the sign of $ g_\mathrm{eff}$ determines the stable configuration: liquid is at the bottom if $ g_\mathrm{eff} > 0$ , and floats above the gas if $ g_\mathrm{eff} < 0$ . This provides a quantitative tool for the configuration prediction under competing drives.
Statistical Mechanics (cond-mat.stat-mech)
7 pages, 4 figures
Uncovering Magnetic Phases with Synthetic Data and Physics-Informed Training
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
Agustin Medina, Marcelo Arlego, Carlos A. Lamas
We investigate the efficient learning of magnetic phases using artificial neural networks trained on synthetic data, combining computational simplicity with physics-informed strategies. Focusing on the diluted Ising model, which lacks an exact analytical solution, we explore two complementary approaches: a supervised classification using simple dense neural networks, and an unsupervised detection of phase transitions using convolutional autoencoders trained solely on idealized spin configurations.
To enhance model performance, we incorporate two key forms of physics-informed guidance. First, we exploit architectural biases which preferentially amplify features related to symmetry breaking. Second, we include training configurations that explicitly break $ \mathbb{Z}_2$ symmetry, reinforcing the network’s ability to detect ordered phases. These mechanisms, acting in tandem, increase the network’s sensitivity to phase structure even in the absence of explicit labels. We validate the machine learning predictions through comparison with direct numerical estimates of critical temperatures and percolation thresholds.
Our results show that synthetic, structured, and computationally efficient training schemes can reveal physically meaningful phase boundaries, even in complex systems. This framework offers a low-cost and robust alternative to conventional methods, with potential applications in broader condensed matter and statistical physics contexts.
Strongly Correlated Electrons (cond-mat.str-el), Artificial Intelligence (cs.AI)
25 pages, 14 figures
Computer simulations show that liquid-liquid phase separation enhances self-assembly
New Submission | Soft Condensed Matter (cond-mat.soft) | 2025-05-16 20:00 EDT
Layne B. Frechette, Naren Sundararajan, Fernando Caballero, Anthony Trubiano, Michael F. Hagan
Biomolecular condensates are liquid- or gel-like droplets of proteins and nucleic acids formed at least in part through liquid-liquid phase separation. Condensates enable diverse functions of cells and the pathogens that infect them, including self-assembly reactions. For example, it has been shown that many viruses form condensates within their host cells to compartmentalize capsid assembly and packaging of the viral genome. Yet, the physical principles controlling condensate-mediated self-assembly remain incompletely understood. In this article we use coarse-grained molecular dynamics simulations to study the effect of a condensate on the assembly of icosahedral capsids. The capsid subunits are represented by simple shape-based models to enable simulating a wide range of length and time scales, while the condensate is modeled implicitly to study the effects of phase separation independent of the molecular details of biomolecular condensates. Our results show that condensates can significantly enhance assembly rates, yields, and robustness to parameter variations, consistent with previous theoretical predictions. However, extending beyond those predictions, the computational models also show that excluded volume enables control over the number of capsids that assemble within condensates. Moreover, long-lived aberrant off-pathway assembly intermediates can suppress yields within condensates. In addition to elucidating condensate-mediated assembly of viruses and other biological structures, these results may guide the use of condensates as a generic route to enhance and control self-assembly in human-engineered systems.
Soft Condensed Matter (cond-mat.soft), Statistical Mechanics (cond-mat.stat-mech), Biological Physics (physics.bio-ph)
*The first two authors contributed equally to this work. Main Text: 19 pages, 10 figures; Supplemental Material: 14 pages, 12 figures; Supplementary Movies available at the following URL: this https URL
Inferring entropy production in many-body systems using nonequilibrium MaxEnt
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-05-16 20:00 EDT
Miguel Aguilera, Sosuke Ito, Artemy Kolchinsky
We propose a method for inferring entropy production (EP) in high-dimensional stochastic systems, including many-body systems and non-Markovian systems with long memory. Standard techniques for estimating EP become intractable in such systems due to computational and statistical limitations. We infer trajectory-level EP and lower bounds on average EP by exploiting a nonequilibrium analogue of the Maximum Entropy principle, along with convex duality. Our approach uses only samples of trajectory observables (such as spatiotemporal correlation functions). It does not require reconstruction of high-dimensional probability distributions or rate matrices, nor any special assumptions such as discrete states or multipartite dynamics. It may be used to compute a hierarchical decomposition of EP, reflecting contributions from different kinds of interactions, and it has an intuitive physical interpretation as a thermodynamic uncertainty relation. We demonstrate its numerical performance on a disordered nonequilibrium spin model with 1000 spins and a large neural spike-train dataset.
Statistical Mechanics (cond-mat.stat-mech), Machine Learning (cs.LG), Adaptation and Self-Organizing Systems (nlin.AO), Neurons and Cognition (q-bio.NC)
Dimensional crossover of class D real-space topological invariants
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Martin Rodriguez-Vega, Terry A. Loring, Alexander Cerjan
The topological properties of a material depend on its symmetries, parameters, and spatial dimension. Changes in these properties due to parameter and symmetry variations can be understood by computing the corresponding topological invariant. Since topological invariants are typically defined for a fixed spatial dimension, there is no existing framework to understand the effects of changing spatial dimensions via invariants. Here, we introduce a framework to study topological phase transitions as a system’s dimensionality is altered using real-space topological markers. Specifically, we consider Shiba lattices, which are class D materials formed by magnetic atoms on the surface of a conventional superconductor, and characterize the evolution of their topology when an initial circular adatom island is deformed into a chain. We also provide a measure of the corresponding protection against disorder. Our framework is generalizable to any symmetry class and spatial dimension, potentially guiding the design of materials by identifying, for example, the minimum thickness of a slab required to maintain three-dimensional topological properties.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Superconductivity (cond-mat.supr-con)
11 pages, 9 figures
Hopf Bifurcation of Nonlinear Non-Hermitian Skin Effect
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Kohei Kawabata, Daichi Nakamura
The non-Hermitian skin effect, nonreciprocity-induced anomalous localization of an extensive number of eigenstates, represents a hallmark of non-Hermitian topological systems with no analogs in Hermitian systems. Despite its significance across various open classical and quantum systems, the influence of nonlinearity has remained largely unclear. Here, we reveal the Hopf bifurcation of the nonlinear skin effect as a critical phenomenon unique to nonlinear non-Hermitian systems. We demonstrate that nonlinearity destabilizes skin states and instead gives rise to the emergence of delocalized states associated with limit cycles in phase space. We also uncover the algebraically localized critical skin effect precisely at the Hopf bifurcation point. We illustrate these behavior in a nonlinear extension of the Hatano-Nelson model in both continuum and lattice. Our work shows a significant role of nonlinearity in the skin effect and uncovers rich phenomena arising from the interplay between non-Hermiticity and nonlinearity.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Optics (physics.optics), Quantum Physics (quant-ph)
8+6 pages, 3+1 figures
Coexistence of charge density wave and field-tuned magnetic states in TmNiC$_2$
New Submission | Strongly Correlated Electrons (cond-mat.str-el) | 2025-05-16 20:00 EDT
Kamil K. Kolincio, Marta Roman, Valerio Tammurello, Simone Di Cataldo, Daniel Matulka, Sonia Francoual, Berthold Stöger, Herwig Michor
Exploring the relations between coexisting, cooperative, or competing types of ordering is a key to identify and harness the mechanisms governing the mutual interactions between them, and to utilize their combined properties. We have experimentally explored the response of the charge density wave (CDW) to various antiferromagnetic, metamagnetic, and field-aligned ferromagnetic states that constitute the magnetic phase diagram of TmNiC$ _2$ . The high resolution x-ray diffraction experiment employing synchrotron radiation at low temperature and high magnetic field, allowed to follow the superstructure satellite reflections, being a sensitive probe of CDW. This investigation not only reveals direct evidence that the charge density wave avoids even a partial suppression in the antiferromagnetic ground state but also proves that this state coexists, without any visible signatures of weakening, in the entire dome of the magnetically ordered phases, including the field-aligned ferromagnetic state. The calculations of the electronic and phonon structures support the experiment, revealing that the dominant contribution to the CDW transition stems from momentum-dependent electron-phonon coupling. We conclude that this mechanism prevents the CDW from vanishing, although the nesting conditions within the magnetically ordered phases deteriorate.
Strongly Correlated Electrons (cond-mat.str-el)
Giant elastoresistance in magic-angle twisted bilayer graphene
New Submission | Mesoscale and Nanoscale Physics (cond-mat.mes-hall) | 2025-05-16 20:00 EDT
Xuetao Ma, Zhaoyu Liu, Jiaqi Cai, Kenji Watanabe, Takashi Taniguchi, Xiaodong Xu, Jiun-Haw Chu, Matthew Yankowitz
Strongly correlated and topological phases in moiré materials are exquisitely sensitive to lattice geometry at both atomic and superlattice length scales. Twist angle, pressure, and strain directly modify the lattice, and thus act as highly effective tuning parameters. Here we examine electrical transport in twisted bilayer graphene subjected to continuous uniaxial strain. Near the magic angle ($ \approx 1.1^{\circ}$ ), devices exhibit a pronounced elastoresistance that depends on band filling and temperature, with a gauge factor more than two orders of magnitude larger than that of conventional metals. In selected doping regimes the elastoresistance exhibits a Curie-Weiss-like temperature divergence. We discuss possible microscopic origins, including nematic fluctuations and enhanced electronic entropy from fluctuating isospin moments. Our work establishes uniaxial strain as a versatile probe of correlated physics in a moiré material.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Strongly Correlated Electrons (cond-mat.str-el)
21 pages, 16 figures
Networked Infectiousness: Cascades, Power Laws, and Kinetics
New Submission | Statistical Mechanics (cond-mat.stat-mech) | 2025-05-16 20:00 EDT
Sara Najem, Leonid Klushin, Jihad Touma
Networked SIR models have become essential workhorses in the modeling of epidemics, their inception, propagation and control. Here, and building on this venerable tradition, we report on the emergence of a remarkable self-organization of infectiousness in the wake of a propagating disease front. It manifests as a cascading power-law distribution of disease strength in networked SIR simulations, and is then confirmed with suitably defined kinetics, then stochastic modeling of surveillance data. Given the success of the networked SIR models which brought it to light, we expect this scale-invariant feature to be of universal significance, characterizing the evolution of disease within and across transportation networks, informing the design of control strategies, and providing a litmus test for the soundness of disease propagation models.
Statistical Mechanics (cond-mat.stat-mech), Adaptation and Self-Organizing Systems (nlin.AO)
Magnon Nesting in Driven Two-Dimensional Quantum Magnets
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Hossein Hosseinabadi, Yaroslav Tserkovnyak, Eugene Demler, Jamir Marino
We uncover a new class of dynamical quantum instability in driven magnets leading to emergent enhancement of antiferromagnetic correlations even for purely ferromagnetic microscopic couplings. A primary parametric amplification creates a frequency-tuned nested magnon distribution in momentum space, which seeds a secondary instability marked by the emergence of enhanced antiferromagnetic correlations, mirroring Fermi surface nesting instabilities in electronic systems. In sharp contrast to the fermionic case, however, the magnon-driven instability is intrinsically non-equilibrium and fundamentally inaccessible in thermal physics. Its quantum mechanical origin sets it apart from classical instabilities such as Faraday and modulation instabilities, which underlie several instances of dynamical behavior observed in magnetic and cold-atom systems.
Materials Science (cond-mat.mtrl-sci), Quantum Gases (cond-mat.quant-gas), Pattern Formation and Solitons (nlin.PS), Quantum Physics (quant-ph)
16 pages, 10 figures
Computational screening and experimental validation of promising Wadsley-Roth Niobates
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Zachary J. L. Bare, CJ Sturgill, Manish Kumar, Iva Milisavljevic, Hans-Conrad zur Loye, Scott Misture, Morgan Stefik, Christopher Sutton
The growing demand for efficient, high-capacity energy storage systems has driven extensive research into advanced materials for lithium-ion batteries. Among the various candidates, Wadsley-Roth (WR) niobates have emerged as a promising class of materials for fast Li+ storage due to rapid ion diffusion within their ReO3-like blocks in combination with good electronic conductivity along the shear planes. Despite the remarkable features of WR phases, there are presently less than 30 known structures which limits identification of structure-property relationships for improved performance as well as the identification of phases with more earth-abundant elements. In this work, we have dramatically expanded the set of potentially (meta)stable compositions (with $ \Delta$ Hd < 22 meV/atom) to 1301 (out of 3283) through high-throughput screening with density functional theory (DFT). This large space of compound was generated through single- and double-site substitution into 10 known WR-niobate prototypes using 48 elements across the periodic table. To confirm the structure predictions, we successfully synthesized and validated with X-ray diffraction a new material, MoWNb24O66. The measured lithium diffusivity in MoWNb24O66 has a peak value of 1.0x10-16 m2/s at 1.45 V vs. Li/Li+ and achieved 225 mAh/g at 5C. Thus a computationally predicted phase was realized experimentally with performance exceeding Nb16W5O55, a recent WR benchmark. Overall, the computational dataset of potentially stable novel compounds and with one realized that has competitive performance provide a valuable guide for experimentalists in discovering new durable battery materials.
Materials Science (cond-mat.mtrl-sci)
Observing Bethe strings in an attractive Bose gas far from equilibrium
New Submission | Quantum Gases (cond-mat.quant-gas) | 2025-05-16 20:00 EDT
Milena Horvath, Alvise Bastianello, Sudipta Dhar, Rebekka Koch, Yanliang Guo, Jean-Sébastien Caux, Manuele Landini, Hanns-Christoph Nägerl
Bethe strings are bound states of constituent particles in a variety of interacting many-body one-dimensional (1D) integrable quantum models relevant to magnetism, nanophysics, cold atoms and beyond. As emergent fundamental excitations, they are predicted to collectively reshape observable equilibrium and dynamical properties. Small individual Bethe strings have recently been observed in quantum magnets and superconducting qubits. However, creating states featuring intermixtures of many, including large, strings remains an outstanding experimental challenge. Here, using nearly integrable ultracold Bose gases, we realize such intermixtures of Bethe strings out of equilibrium, by dynamically tuning interactions from repulsive to attractive. We measure the average binding energy of the strings, revealing the presence of bound states of more than six particles. We find further evidence for them in the momentum distribution and in Tan’s contact, connected to the correlated density. Our data quantitatively agree with predictions from generalized hydrodynamics (GHD). Manipulating intermixtures of Bethe strings opens new avenues for understanding quantum coherence, nonlinear dynamics and thermalization in strongly-interacting 1D systems.
Quantum Gases (cond-mat.quant-gas), Statistical Mechanics (cond-mat.stat-mech), Quantum Physics (quant-ph)
Low-temperature structural instabilities of the halide double perovskite Cs$_2$AgBiBr$_6$ investigated via x-ray diffraction and infrared phonons
New Submission | Materials Science (cond-mat.mtrl-sci) | 2025-05-16 20:00 EDT
Collin Tower, Fereidoon S. Razavi, Jeremy Dion, Jürgen Nuss, Reinhard K. Kremer, Maureen Reedyk
The halide double perovskite Cs$ _2$ AgBiBr$ _6$ has been proposed as a potential replacement for organic halide perovskites for photovoltaic applications. Further investigation of its dielectric response, optical properties and structural stability is thus warranted. Cs$ _2$ AgBiBr$ _6$ exhibits a well-documented structural phase transition at 120 K but indications for an additional lower temperature ($ \sim$ 40 K) phase transition have also been reported. On the basis of measurements of the specific heat capacity, temperature dependent powder X-ray diffraction, low frequency capacitance, and infrared reflectivity we clarify the previously reported splitting of phonon modes in the Raman spectrum at $ \sim$ 40 K as due to a subtle structural phase transition from the tetragonal I4/m structure to a monoclinic $ P12_1$ /$ n1$ crystal structure. The infrared active vibrational modes are experimentally investigated in the three structural regimes. In the cubic structure at room temperature the four IR active modes are observed at 135,$ \sim$ 95, 55, and $ \sim$ 25 cm$ ^{-1}$ , as the symmetry reduces to tetragonal a minute splitting of these modes is expected, however below 40 K an additional mode is observed indicating a further reduction in symmetry.
Materials Science (cond-mat.mtrl-sci)
18 Pages, 16 Figures