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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 22 October

Materials Science

Synergistic effects of rare-earth doping on the magnetic properties of orthochromates: A machine learning approach

Guanping Xu, Zirui Zhao, Muqing Su et al. (+1 more)

Multiferroic materials, particularly rare-earth orthochromates (RECrO$_3$), have garnered significant interest due to their unique magnetic and electric-polar properties, making them promising candidates for multifunctional devices. Although extensive research has been conducted on their antiferromagnetic (AFM) transition temperature (N$\acute{\textrm{e}}$el temperature, $T_\textrm{N}$), ferroelectricity, and piezoelectricity, the effects of doping and substitution of rare-earth (RE) elements on these properties remain insufficiently explored. In this study, convolutional neural networks (CNNs) were employed to predict and analyze the physical properties of RECrO$_3$ compounds under various doping scenarios. Experimental and literature data were integrated to train machine learning models, enabling accurate predictions of $T_\textrm{N}$, besides remanent polarization ($P_\textrm{r}$) and piezoelectric coefficients ($d_{33}$). The results indicate that doping with specific RE elements significantly impacts $T_\textrm{N}$, with optimal doping levels identified for enhanced performance. Furthermore, high-entropy RECrO$_3$ compounds were systematically analyzed, demonstrating how the inclusion of multiple RE elements influences magnetic properties. This work establishes a robust framework for predicting and optimizing the properties of RECrO$_3$ materials, offering valuable insights into their potential applications in energy storage and sensor technologies.
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All authors Guanping Xu, Zirui Zhao, Muqing Su, Hai-Feng Li

Materials Science

Exciton thermal radiation from structure-sorted carbon nanotube membranes

Akiteru Takahashi, Kaichi Teranishi, Shonosuke Takaichi et al. (+2 more)

Owing to their small binding energies, excitons in bulk semiconductors typically exhibit a sharp optical peak at low temperatures only. This limitation can be overcome by single-walled carbon nanotubes (SWCNTs) and other low-dimensional semiconductors with highly enhanced exciton binding energies. Exciton thermal radiation, which can potentially be exploited for selective thermal emission and energy harvesting, has been recently observed in individual SWCNTs heated under photoirradiation. However, whether macroscale-SWCNT assemblies can emit exciton thermal radiation under conduction heating remains unclear and constitutes an important challenge for practical applications. Herein, we observed peaked exciton thermal radiation from structure-sorted SWCNT membranes. Transmission spectroscopy showed robust exciton resonance at high temperatures, resulting in clear exciton resonance in the thermal radiation band. The absolute emissivity spectra of the membranes were determined at 850 K. Exciton dominance suppresses the contribution of thermal free carriers to the infrared absorption/emission spectra, maintaining the transparency below the optical gap even at elevated temperatures. These phenomena are not observed in bulk semiconductors, highlighting the structure-sorted SWCNT membranes as unique semiconductors leveraging stable exciton resonances at elevated temperatures.
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All authors Akiteru Takahashi, Kaichi Teranishi, Shonosuke Takaichi, Taishi Nishihara, Yuhei Miyauchi

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Many-Body Floquet Theory for Radiative Heat Transfer in Time-Modulated Systems

Riccardo Messina and Philippe Ben-Abdallah

We develop a general theory of radiative heat exchange between dipoles with time-modulated optical properties. This framework extends fluctuational electrodynamics beyond equilibrium by incorporating nonstationary correlations and memory effects induced by temporal modulation. Closed-form expressions for the heat currents in modulated many-body systems are obtained, together with a generalized Landauer-like formulation of the pairwise exchanges, where the transmission coefficient accounts for all inelastic frequency-conversion channels. Near-resonant modulation redistributes and amplifies thermal fluctuations across Floquet sidebands, acting as a parametric amplifier of thermal radiation and enabling active, frequency-selective control of nanoscale heat transfer.
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Mesoscale and Nanoscale Physics

Mapping the twist angle dependence of quasi-Brillouin zones in doubly aligned graphene/BN heterostructures

Jorge Vallejo Bustamante, Viet-Hung Nguyen, Liam S. Farrar et al. (+5 more)

When monolayer graphene is crystallographically aligned to hexagonal boron nitride (BN), a moiré superlattice is formed, producing characteristic satellite Dirac peaks in the electronic band structure. Aligning a second BN layer to graphene creates two coexisting moiré patterns, which can interfere to produce periodic, quasi-periodic or non-periodic superlattices, depending on their relative alignment. Here, we investigate one of the simplest realizations of such a double-moiré structure, graphene encapsulated between two BN layers, using dynamically rotatable van der Waals heterostructures. Our setup allows in situ control of the top BN alignment while keeping the bottom BN fixed. By systematically mapping the charge transport as a function of BN angular alignment, we identify the simultaneous signatures of the original moirés, super-moirés, and a third set of features corresponding to quasi-Brillouin zones (qBZ) formed when the system's periodicity becomes ill-defined. Comparing our measurements with theoretical models, we provide the first experimental mapping of the qBZs as a function of angular alignment. Our results establish a direct experimental link between moiré interference and qBZ formation, opening new avenues for engineering electronic structures in multi-aligned 2D heterostructures.
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All authors Jorge Vallejo Bustamante, Viet-Hung Nguyen, Liam S. Farrar, Kenji Watanabe, Takashi Taniguchi, Dominique Mailly, Jean-Christophe Charlier, Rebeca Ribeiro-Palau

Materials Science · Cross-listed from physics.chem-ph

Identifying the Catalytic Descriptor of Single-Atom Catalysts in Nitrate Reduction Reaction: An Interpretable Machine-Learning Method

Zhen Zhu, Shan Gao, Jing Zhang et al. (+3 more)

Elucidating the catalytic descriptor that accurately characterizes the structure-activity relationships of typical catalysts for various important heterogeneous catalytic reactions is pivotal for designing high-efficient catalytic systems. Here, an interpretable machine learning technique was employed to identify the key determinants governing the nitrate reduction reaction ($\rm NO_3RR$) performance across 286 single-atom catalysts (SACs) with the active sites anchored on double-vacancy $\rm BC_3$ monolayers. Through Shapley Additive Explanations (SHAP) analysis with reliable predictive accuracy, we quantitatively demonstrated that, favorable $\rm NO_3RR$ activity stems from a delicate balance among three critical factors: low $\rm N_V$, moderate $\rm D_N$, and specific doping patterns. Building upon these insights, we established a descriptor ($\psi$) that integrates the intrinsic catalytic properties and the intermediate O-N-H angle ($\theta$), effectively capturing the underlying structure-activity relationship. Guided by this, we further identified 16 promising catalysts with predicted low limiting potential ($U_{\rm L}$). Importantly, these catalysts are composed of cost-effective non-precious metal elements and are predicted to surpass most reported catalysts, with the best-performing Ti-V-1N1 is predicted to have an ultra-low $U_{\rm L}$ of $-0.10$ V.
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All authors Zhen Zhu, Shan Gao, Jing Zhang, Xuxin Kang, Shunfang Li, Xiangmei Duan

Statistical Mechanics · Cross-listed from quant-ph

Decoherence of a dissipative Brownian charged magneto-anharmonic oscillator: an information theoretic approach

Suraka Bhattacharjee, Koushik Mandal and Supurna Sinha

We study the decoherence of an anisotropic anharmonic oscillator in a magnetic field, coupled to a bath of harmonic oscillators at high and low temperatures. We solve the anharmonic oscillator problem using perturbative techniques and derive the non-Markovian master equation in the weak coupling limit. The anharmonicity parameter {\alpha} enhances decoherence due to the deconfining effect of anharmonicity. The oscillatory nature of the time evolution of heating function indicates information backflow. The von-Neumann entropy is also calculated for the system, which increases with {\alpha}, consistent with the deconfining effect noted in the decoherence analysis. We have also proposed a cold ion experimental set up for testing our theoretical predictions. The study is of relevance to the domain of quantum technology where decoherence significantly affects the performance of a quantum computer.
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Superconductivity

Time-reversal symmetry breaking superconductivity in the presence of loop-current fluctuations

Zenghui Fan, Runyu Ma, Stefano Chesi et al. (+2 more)

Loop currents have been proposed in various superconductors and recently confirmed in kagome materials, raising a fundamental question regarding their intrinsic connection to superconductivity. Here, we study a sign-problem-free bilayer $t-J_{\perp}-V$ model hosting a spontaneous interlayer loop-current parent state, and explore the interplay between loop-current fluctuations and superconductivity using unbiased projector quantum Monte Carlo simulations. Near half-filling, unbiased interlayer interactions induce spontaneous loop currents that break time-reversal symmetry. Upon hole doping, the loop-current order is suppressed, and interlayer $s$-wave superconductivity emerges where loop-current fluctuations become dominant. We establish a phase diagram revealing a transition from the loop-current parent to a superconducting state, reminiscent of the evolution from an antiferromagnetic parent to superconductivity in cuprates. Strikingly, a coexisting regime emerges near the phase boundary, yielding time-reversal-symmetry-breaking superconductivity. Our study reveals an intrinsic connection between loop currents and superconductivity, and identifies a promising mechanism for time-reversal symmetry breaking in superconductors. Furthermore, our results offer insights into unconventional superconductivity in loop-current systems and establish a minimal theoretical framework for understanding time-reversal symmetry breaking in bilayer correlated electron systems.
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All authors Zenghui Fan, Runyu Ma, Stefano Chesi, Congjun Wu, Tianxing Ma

Materials Science

Synthesizability Prediction of Crystalline Structures with Structure-Aware Feature Learning and Uncertainty Quantification

Danial Ebrahimzadeh, Sarah Sharif and Yaser Mike Banad

Predicting which hypothetical inorganic crystals can be experimentally realized remains a central challenge in accelerating materials discovery. SyntheFormer is a positive-unlabeled framework that learns synthesizability directly from crystal structure, combining Fourier-transformed crystal properties (FTCP) representation with structure-aware feature extraction, Random-Forest feature selection, and a compact deep MLP classifier. The model is trained on historical data from 2011 through 2018 and evaluated prospectively on future years from 2019 to 2025, where the positive class constitutes only 1.02 percent of samples. Under this temporally separated evaluation, SyntheFormer achieves a test AUC of 0.735, AUPRC of 0.099 and 97.6 percent recall at 94.2 percent coverage with dual-threshold calibration. Direct prospective validation supports this result as two materials that were unlabeled at the time of data curation, Y6Fe(SiS7)2 and BaYb2F8, were assigned high SyntheFormer scores (0.961 and 0.753, respectively) and were subsequently reported experimentally. Crucially, the model recovers experimentally confirmed metastable compounds that lie far from the convex hull and simultaneously assigns low scores to many thermodynamically stable yet unsynthesized candidates, demonstrating that stability alone is insufficient to predict experimental attainability.
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Statistical Mechanics · Cross-listed from cs.SI

Belief propagation for finite networks using a symmetry-breaking source node

Seongmin Kim and Alec Kirkley

Belief Propagation (BP) is an efficient message-passing algorithm widely used for inference in graphical models and for solving various problems in statistical physics. However, BP often yields inaccurate estimates of order parameters and their susceptibilities in finite systems, particularly in sparse networks with few loops. Here, we show for both percolation and Ising models that fixing the state of a single well-connected "source" node to break global symmetry substantially improves inference accuracy and captures finite-size effects across a broad range of networks, especially tree-like ones, at no additional computational cost.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Symmetry-Adapted Eigensolver from Real-Space Sampling of Tensor-Network-Bridged Quantum Circuits

Lei Xu and Ling Wang

We propose a symmetry-adapted eigensolver for strongly correlated systems that separates where the wave function is sampled from where it is defined. The lattice is divided into equal blocks: parallel quantum circuits absorb the entanglement within each block, while a matrix product state (MPS) backbone bridges the blocks and restores global correlations. The resulting real-space amplitude $\phi(a_{\rm real})$ acts only as a sample generator—configurations are drawn from $|\phi(a_{\rm real})|^2$ directly, block by block, without any Markov chain. The variational state itself is defined in a symmetry-adapted basis by two separate rules: the modulus of $\psi(a_{\rm symm})$ is the square root of the total weight accumulated over the entire equivalence class, $\widetilde{p}(a_{\rm symm})=\sum_{a_{\rm real}\in\{g a_{\rm repr}\}}|\phi(a_{\rm real})|^2$, whereas its phase is inherited from the single representative amplitude $\phi(a_{\rm repr})$. The modulus rule is what makes the scheme both exact and cheap: the distribution$\widetilde{p}(a_{\rm symm})$ sampled in the symmetric basis is exactly the one induced by the mapping from the real-space distribution $p(a_{\rm real})$, so every generated configuration is an unbiased sample of $|\psi(a_{\rm symm})|^2$; the phase rule then fixes the only freedom that remains. Because amplitudes within a class are combined in probability rather than summed with symmetry characters, $\psi$ is not a group projection of the circuit-MPS state; the class-wide aggregation instead supplies long-range, symmetry-enforced entanglement that the MPS never has to carry itself.
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Materials Science

High-Efficiency Nonrelativistic Charge-Spin Conversion in X-Type Antiferromagnets

Jiabin Wang, Wancheng Zhang, Zhenhua Zhang et al. (+3 more)

Antiferromagnetic materials with spin splitting have attracted considerable attention for their symmetry-enabled anisotropic spin textures that sustain a zero net magnetization, thereby facilitating efficient spin-current generation. In this work, the highly efficient generation of nonrelativistic spin currents is demonstrated to be facilitated by the distinctive Fermi surface geometry of X-type collinear antiferromagnets. As a prototype conducting X-type antiferromagnet, the Fermi surface of $\beta-\mathrm{Fe_2PO_5}$ exhibits a distinct $d$-wave altermagnetic characteristic, which compresses into a nearly X-shaped configuration. This results in highly efficient spin currents, achieving a charge-spin conversion efficiency of up to 90%. Moreover, the spin current polarization is controlled by the orientation of the Néel vector. When the Néel vector tilts to the out-of-plane direction, an in-plane injected charge current can generate a special spin current component with both spin polarization and propagation along the out-of-plane direction, whose charge-spin conversion efficiency substantially exceeds that of known ferromagnets, altermagnets, noncollinear antiferromagnets, and low-symmetry materials. The highly efficient charge-spin conversion in X-type antiferromagnets provides a novel and highly effective spin source system for the development of low-power spintronic devices.
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All authors Jiabin Wang, Wancheng Zhang, Zhenhua Zhang, Rui Xiong, Yong Liu, Zhihong Lu

Strongly Correlated Electrons

Calculating the Luttinger liquid parameter for an interacting Kitaev chain quantum simulator

Troy Losey, Jin Zhang and S.-W. Tsai

In this work, we introduce a solid-state platform for building quantum simulators using implanted spin centers in solid-state materials. We build upon the proposal for an $S=1$ chain of spin centers coupled through the magnetic dipole-dipole interaction and subjected to an external magnetic field as a quantum simulator for critical floating phases. We introduce another magnetic field and map the system to the interacting Kitaev chain. This setup, tunable through the applied fields and the orientation of the spin centers within the crystal, exhibits a variety of rich quantum behavior which notably includes floating phases, a $Z_2$ symmetry-breaking phase, and lines of both Berezinskii-Kosterlitz-Thouless (BKT) and Pokrovsky-Talapov transitions. Furthermore, we employ several novel methods to calculate the Luttinger liquid parameter in our model with incommensurate correlations. We find that these methods provide a route to identify BKT transitions with less computational resources than utilizing entanglement entropy and central charge.
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Materials Science

Transient Absorption Spectroscopy of NbOI$_2$

Salman Ahsanullah, Neema Rafizadeh and Hui Zhao

NbOI$_2$ has recently emerged as a new van der Waals material combining semiconducting behavior with intrinsic in plane ferroelectricity and pronounced transport and optical anisotropy. However, its photocarrier dynamics remain largely unexplored. Here we report transient absorption spectroscopy of NbOI$_2$ using femtosecond pump probe reflectance measurements. A pronounced transient absorption feature is observed near the 2.34 eV excitonic resonance, arising from photocarrier induced excitonic energy shifts and saturation. The decay dynamics reveal an exciton lifetime of several tens of picoseconds and show density-dependent behavior consistent with exciton exciton annihilation and defect-assisted Auger recombination, yielding a rate of 0.4 cm$^2$ s$^{-1}$, which is comparable to that in monolayer transition metal dichalcogenides. Polarization resolved measurements further reveal a pronounced in-plane anisotropy in the transient response that follows the linear absorption anisotropy. These findings provide fundamental insight into photocarrier dynamics in NbOI$_2$ and establish key parameters for understanding and exploiting its optoelectronic behavior.
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Disordered Systems and Neural Networks

Dynamical mean field approach to associative memory model with non-monotonic transfer functions

Yoshiyuki Kabashima and Kazushi Mimura

The Hopfield associative memory model stores random patterns in synaptic couplings according to Hebb's rule and retrieves them through gradient descent on an energy function. This conventional setting, where neurons are assumed to have monotonic transfer functions, has been central to understanding associative memory. Morita (1993, Neural Netw. 6 115), however, showed that introducing non-monotonic transfer functions can dramatically enhance retrieval performance. While this phenomenon has been qualitatively examined, a full quantitative theory remains elusive due to the difficulty of analysis in the absence of an underlying energy function. In this work, we apply dynamical mean-field theory to the discrete-time synchronous retrieval dynamics of the non-monotonic model, which succeeds in accurately characterizing its macroscopic dynamical properties. We also derive conditions for retrieval states, and clarify their relation to previous studies. Our results provide new insights into the non-equilibrium retrieval dynamics of associative memory models.
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Mesoscale and Nanoscale Physics

Control of out-of-plane anti-damping spin torque with a canted ferromagnetic spin source

Xiaoxi Huang, Daniel A. Pharis, Hang Zhou et al. (+13 more)

To achieve efficient anti-damping switching of nanoscale magnetic memories with perpendicular magnetic anisotropy using spin-orbit torque requires that the anti-damping spin-orbit torque have a strong out-of-plane component. The spin anomalous Hall effect and the planar Hall effect spin current produced by a ferromagnetic layer are candidate mechanisms for producing such an out-of-plane anti-damping torque, but both require that the magnetic moment of the spin source layer be canted partly out of the sample plane at zero applied magnetic field. Here we demonstrate such a canted configuration for a ferromagnetic SrRuO3 layer and we characterize all vector components of the torque that it produces, including non-zero out-of-plane anti-damping torques. We verify that the out-of-plane spin component can be tuned by the orientation of magnetic moment, with significant contributions from both the spin anomalous Hall effect and the planar Hall effect spin current.
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All authors Xiaoxi Huang, Daniel A. Pharis, Hang Zhou, Zishen Tian, Thow Min Jerald Cham, Kyoungjun Lee, Yilin Evan Li, Chaoyang Wang, Yuhan Liang, Maciej Olszewski, Di Yi, Chang-Beom Eom, Darrell G. Schlom, Lane W. Martin, Ding-Fu Shao, Daniel C. Ralph

Tuesday 21 October

Quantum Gases · Cross-listed from hep-lat

Repulsively Bound Hadrons in a $\mathbb{Z}_2$ Lattice Gauge Theory

Sayak Guha Roy, Vaibhav Sharma, Kaidi Xu et al. (+3 more)

The $\mathbb{Z}_2$ lattice gauge theory is a paradigmatic model that exhibits gauge-field-mediated-confinement of pairs of particles into mesons, drawing connections to quantum chromodynamics. In the absence of any additional attractive interactions between particles, mesons are not known to bind in this model. Here, we show that resonant pair-production terms give rise to two separate mechanisms to form stable “hadron” bound states of two mesons: either induced by an effective attractive interaction, or a new dynamical binding mechanism induced by an effective repulsion. The repulsively bound hadron is a high-energy state stabilized by being energetically separated from the two-meson continuum through quantum fluctuations of the gauge fields. We study the dynamical formation of this bound state starting from local excitations. We use matrix product state techniques based on the time-evolving block decimation algorithm to perform our numerical simulations and analyze the effect of model parameters on hadron formation. Furthermore, we derive an effective model that explains its formation. Our findings are amenable to experimental observation on modern quantum hardware such as superconducting qubits, trapped ions, and Rydberg atom arrays.
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All authors Sayak Guha Roy, Vaibhav Sharma, Kaidi Xu, Umberto Borla, Jad C. Halimeh, Kaden R. A. Hazzard

Materials Science

Vertex and front-tracking methods for the modeling of microstructure evolution at the solid state: a brief review

Marc Bernacki

In mesoscopic scale microstructure evolution modeling, two primary numerical frameworks are used: Front-Capturing (FC) and Front-Tracking (FT) ones. FC models, like phase-field or level-set methods, indirectly define interfaces by tracking field variable changes. On the contrary, FT models explicitly define interfaces using interconnected segments or surfaces. In historical FT methodologies, Vertex models were first developed and consider the description of the evolution of polygonal structures in terms of the motion of points where multiple boundaries meet. Globally, FT-type approaches, often associated with Lagrangian movement, enhance spatial resolution in 3D surfacic and 2D lineic problems using techniques derived from finite element meshing and remeshing algorithms. These efficient approaches, by nature, are well adapted to physical mechanisms correlated to interface properties and geometries. They also face challenges in managing complex topological events, especially in 3D. However, recent advances highlight their potential in computational efficiency and analysis of mobility and energy properties, with possible applications in intragranular phenomena.
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Statistical Mechanics

Dynamic Phase Transitions in Mean-Field Ginzburg-Landau Models: Conjugate Fields and Fourier-Mode Scaling

Yelyzaveta Satynska and Daniel T. Robb

Dynamic phase transitions of periodically forced mean-field ferromagnets are often described by a single order parameter and a scalar conjugate field. Building from previous work, we show that, at the critical period $P_c$ of the mean-field Ginzburg-Landau (MFGL) dynamics with energy $F(m)=am^2+bm^4-hm$, the correct conjugate field is the entire even-Fourier component part of the applied field. The correct order parameter is $z_k=\sqrt{\bigl|\,m_k^2-|m_{k,c}|^2\,\bigr|}$, where $m_k$ is the $k^{th}$ Fourier component of the magnetization m(t), and $m_{k,c}$ is the $k^{th}$ Fourier component at the critical period. Using high-accuracy limit-cycle integration and Fourier analysis, we first confirm that, for periodic fields that contain only odd components, the symmetry-broken branch below $P_c$ exhibits $z_k \propto \varepsilon^{1/2}$ (computationally tested for modes $k\le30$), where $\varepsilon=(P_c-P)/P_c$. This provides strong evidence that the 1/2 scaling holds for all Fourier modes. We then find three robust facts: (1) Exactly at $P_c$, adding a small perturbation composed of even Fourier components with an overall field multiplier $h_{mult}$ yields $z_k \propto h_{mult}^{1/3}$ across many $k$. (2) Mode-resolved deviations obey a parity rule: $|\delta m_{2n}| \propto h_{mult}^{1/3}$ and $|\delta m_{2n+1}| \propto h_{mult}^{2/3}$. (3) These scalings persist in two MFGL models with higher-order nonlinearities.
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Strongly Correlated Electrons

Many-Body Perturbation Theory for Driven Dissipative Quasiparticle Flows and Fluctuations

Thomas Blommel, Enrico Perfetto, Gianluca Stefanucci et al. (+1 more)

We present a unified many-body perturbation theory for open quantum systems, that treats dissipation, correlations, and external driving on equal footing. Using a Keldysh-Lindblad formalism, we introduce diagrammatic treatment of dissipative interaction lines representing quasiparticle flows and fluctuations. Two new Feynman rules render the evaluation of dissipative diagrams compact and systematically improvable, while preserving the Keldysh and anti-Hermitian symmetries of the closed-system theory. Consequently, the structure of the Kadanoff-Baym equations (KBE) remains unchanged, enabling existing numerical methods to be directly applied. To illustrate this, we derive dissipative versions of the second Born and $GW$ approximations, identifying the physical content of the self-energy components. Moreover, we demonstrate that time-linear approximations to the full KBE retain their closed structure and can be efficiently used to simulate relaxation and decoherence dynamics. The impact of dissipation-induced correlations is illustrated in the driven Haldane model, where quasiparticles exhibit nontrivial stabilization and acquire lifetimes that far exceed those of the bare system. This framework establishes a general route toward first-principles modeling of correlated, driven, and dissipative quantum materials.
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All authors Thomas Blommel, Enrico Perfetto, Gianluca Stefanucci, Vojtech Vlcek

Materials Science · Cross-listed from physics.ins-det

Quantitative measurement of magnetic dichroic signals at sub-nanometer to atomic scale resolution conditions

Sharath Kumar Manjeshwar Sathyanath, Anna L. Ravensburg, Vassilios Kapaklis et al. (+3 more)

When aiming for atomic resolution electron magnetic circular dichroism (EMCD) in STEM mode, the high convergence angle of the electron probe can lead to unforeseen artefacts and strong reductions of the signal to noise ratio (SNR) in the measurement of magnetic magnitudes. In this work, the EMCD signal is measured in STEM mode at semi-convergence angles ranging from \alpha=\ 2-10\ mrad\ using iron samples with high structural perfection. We observe that the relative EMCD signal remains very similar for all convergence angles, which is in good agreement with simulations. The improvement in the signal-to-noise ratio as compared to earlier works is due to better crystalline quality of the Fe sample, high control of the sample orientation, better control over sample thickness, and factors such as higher beam current and the use of a fast and sensitive hybrid-pixel electron detector. One of the key factors to remove experimental ambivalences is the use of an acquisition geometry where the two conjugate EMCD spectra are acquired simultaneously. Furthermore the high crystalline quality Fe sample enables the acquisition of statistical entities of spectra at the same sample orientation, which in turn results in high SNR EMCD signals. We obtain high SNR EMCD signals for all semi convergence angles and could measure the orbital to spin magnetic moment ratio ml/ms with high precision. We observed that at high convergence angles, the ml/ms ratio gets sensitive to minute changes in sample orientation.
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All authors Sharath Kumar Manjeshwar Sathyanath, Anna L. Ravensburg, Vassilios Kapaklis, Jan Rusz, Björgvin Hjörvarsson, Klaus Leifer

Materials Science · Cross-listed from physics.chem-ph

Ab Initio Free Energy Surfaces for Coupled Ion-Electron Transfer

Ethan Abraham, Martin Z. Bazant and Troy Van Voorhis

Although coupled ion-electron transfer (CIET) has emerged as a powerful framework to rationalize the kinetics of Faradaic reactions, its mechanism has lacked a fully microscopic, first-principles description. Here we show that the coupling of electron-transfer to ion-transfer can be understood as an extension of Marcus theory in which the ensemble of diabatic nuclear configurations is conditioned on a classical collective variable describing the interfacial anisotropy. This formalism enables direct construction of the CIET free-energy surface from constrained ab initio trajectories, providing a first-principles route to electrochemical current-overpotential relations. We demonstrate this method for CO2 redox on a gold electrode and find that the resulting two-dimensional saddle-point barriers differ substantially from one-dimensional treatments that consider only electron- or ion-transfer coordinates individually.
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Disordered Systems and Neural Networks

On the relationship between equilibria and dynamics in large, random neuronal networks

Xiaoyu Yang, Giancarlo La Camera and Gianluigi Mongillo

We investigate the equilibria of a random model network exhibiting extensive chaos. In this regime, a large number of equilibria is present. They are all saddles with an extensive, but fractionally-small, number of unstable directions. Despite network's connectivity being completely random, the equilibria are strongly correlated and, as a result, they occupy a small region in the phase space. The attractor is inside this region. This geometry explains why the chaotic dynamics in these models can be described by a fractionally-small number of collective modes.
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Soft Condensed Matter

Learning noisy tissue dynamics across time scales

Ming Han, John Devany, Michel Fruchart et al. (+2 more)

Tissue dynamics play a crucial role in biological processes ranging from inflammation to morphogenesis. However, these noisy multicellular dynamics are notoriously hard to predict. Here, we introduce a biomimetic machine learning framework capable of inferring noisy multicellular dynamics directly from experimental movies. This generative model combines graph neural networks, normalizing flows and WaveNet algorithms to represent tissues as neural stochastic differential equations where cells are edges of an evolving graph. Cell interactions are encoded in a dual signaling graph capable of handling signaling cascades. The dual graph architecture of our neural networks reflects the architecture of the underlying biological tissues, substantially reducing the amount of data needed for training, compared to convolutional or fully-connected neural networks. Taking epithelial tissue experiments as a case study, we show that our model not only captures stochastic cell motion but also predicts the evolution of cell states in their division cycle. Finally, we demonstrate that our method can accurately generate the experimental dynamics of developmental systems, such as the fly wing, and cell signaling processes mediated by stochastic ERK waves, paving the way for its use as a digital twin in bioengineering and clinical contexts.
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All authors Ming Han, John Devany, Michel Fruchart, Margaret L. Gardel, Vincenzo Vitelli

Statistical Mechanics · Cross-listed from hep-th

Towards a Quintic Ginzburg-Landau Description of the $(2,7)$ Minimal Model

Andrei Katsevich, Igor R. Klebanov, Zimo Sun et al. (+1 more)

We discuss dimensional continuation of the massless scalar field theory with the $i\phi^5$ interaction term. It preserves the so-called $\mathcal{PT}$ symmetry, which acts by $\phi\rightarrow -\phi$ accompanied by $i\rightarrow -i$. Below its upper critical dimension $10/3$, this theory has interacting infrared fixed points. We argue that the fixed point in $d=2$ describes the non-unitary minimal conformal model $M(2,7)$. We identify the operators $\phi$ and $\phi^2$ with the Virasoro primaries $\phi_{1,2}$ and $\phi_{1,3}$, respectively, and $i\phi^3$ with a quasi-primary operator, which is a Virasoro descendant of $\phi_{1,3}$. Our identifications appear to be consistent with the operator product expansions and with considerations based on integrability. Using constrained Padé extrapolations, we provide estimates of the critical exponents in $d=3$. We also comment on possible lattice descriptions of $M(2,7)$ and discuss RG flows to and from this CFT. Finally, we conjecture that the minimal models $M(2, 2n+1)$ are described by the massless scalar field theories with the $i\phi^{2n-1}$ interaction terms.
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All authors Andrei Katsevich, Igor R. Klebanov, Zimo Sun, Grigory Tarnopolsky

Strongly Correlated Electrons

Inter-orbital spin-triplet superconductivity from altermagnetic fluctuations

Chen Lu, Chuang Li, Chao Cao et al. (+3 more)

Altermagnetic (AM) fluctuations are a new class of collinear spin fluctuations whose role in mediating superconductivity faces a fundamental tension: their $\Gamma$-point peak favors intra-orbital spin-triplet pairing, while their spin compensation favors inter-orbital singlets. Here, we demonstrate that inversion-symmetry-broken AM fluctuations generically resolve this competition in favor of spin-triplet pairing. As a proof of concept, we study a minimal two-orbital model with two van Hove singularities. The broken inversion symmetry induces momentum-orbital locking: the same orbital dominates at opposite momenta, enhancing the triplet channel. Crucially, a subdominant fluctuation channel arising from inter-van-Hove nesting provides an internal Josephson coupling that locks the phase difference between triplet pairs on different orbitals. We find this coupling changes sign ($+$ to $-$) upon a crossover from AM-dominant to ferromagnetic-dominant fluctuations. The resulting $\pi$-phase difference manifests as a $\tau_z$-type order parameter, $c_{k,1\uparrow}c_{-k,1\uparrow} - c_{k,2\uparrow}c_{-k,2\uparrow}$. Although intra-orbital in the original basis, its orbital-nontrivial character, as manifested by its equivalence to inter-orbital pairing under rotation, defines a general inter-orbital spin-triplet superconductivity. This state is distinct from the $\tau_0$-triplet pairing mediated by ferromagnetic fluctuations, as evidenced by the canceled intra-orbital supercurrent in a Josephson junction between them.
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All authors Chen Lu, Chuang Li, Chao Cao, Huiqiu Yuan, Fu-Chun Zhang, Lun-Hui Hu

Materials Science

First-principles calculation of electronic and topological properties of low-dimensional tellurium

Gabriel Elyas Gama Araujo and Andreia Luisa da Rosa

We present a comprehensive first-principles investigation of the structural, electronic, vibrational, and topological properties of tellurium across its dimensional hierarchy, including bulk trigonal Te-I, two-dimensional tellurene polymorphs, and one-dimensional helical nanowires. Using density functional theory with full inclusion of spin-orbit coupling, we confirm that bulk Te-I is a narrow-gap semiconductor hosting Weyl nodes arising from broken inversion symmetry and degenerate phonon modes suggestive of chiral phonon behavior. In contrast, two-dimensional alpha and beta-tellurene are found to be topologically trivial, with no spin-orbit-driven band inversion in the occupied manifold. Beyond these established phases, we find that buckled kagome and buckled square tellurene lattices exhibit a nontrivial two-dimensional topology of the occupied electronic bands, indicating incipient quantum spin Hall character in metallic systems. In contrast, one-side hydrogen-passivated hexagonal tellurene realizes a fully gapped quantum spin Hall phase with a robust Z2 = 1 invariant, preserved under applied strain and chemical functionalization. In the one-dimensional limit, helical tellurium nanowires preserve chirality and host edge-localized states accompanied by pronounced anisotropy in carrier effective masses. These results establish tellurium as a highly tunable platform for engineering topological phenomena across dimensionality, bridging three-dimensional Weyl physics, two-dimensional quantum spin Hall and incipient Z2 phases, and one-dimensional helical systems.
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Mesoscale and Nanoscale Physics

Sliding Disassembly of van der Waals Heterostructures

Jordan Pack, Karl V. Falb, Sanat Ghosh et al. (+13 more)

Many recent advances in our understanding of two-dimensional (2D) electron systems stem from van der Waals (vdW) heterostructures. The assembly process relies on the weak bonding across interfaces between layered vdW compounds, making it possible to construct exceptionally clean heterostructures from chemically and structurally distinct materials - a challenging task for traditional thin-film growth techniques. Here we demonstrate an additional, dynamic degree of freedom afforded by vdW interfaces, wherein we use microstructured polymer stamps to disassemble and reconfigure vdW heterostructures by sliding. We apply this technique to alter the dielectric environment of monolayer graphene, perform scanning tunneling microscopy on semiconducting and air-sensitive monolayers, and manipulate strain-sensitive moiré materials. Together these demonstrations suggest a new paradigm for assembling and dynamically modifying van der Waals heterostructures, with the potential to reveal new insights into 2D electron systems.
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All authors Jordan Pack, Karl V. Falb, Sanat Ghosh, Xuehao Wu, Keng Tou Chu, Florie Mesple, Ellis Thompson, Zhuquan Zhang, Carolin Gold, Kenji Watanabe, Takashi Taniguchi, Dmitri N. Basov, A. N. Pasupathy, Matthew Yankowitz, Cory R. Dean, Aravind Devarakonda

Mesoscale and Nanoscale Physics

iDART: Interferometric Dual-AC Resonance Tracking nano-electromechanical mapping

J. Bemis, F. Wunderwald, U. Schroeder et al. (+3 more)

Piezoresponse force microscopy (PFM) has established itself as a very successful and reliable imaging and spectroscopic tool for measuring a wide variety of nanoscale electromechanical functionalities. Quantitative imaging of nanoscale electromechanical phenomena requires high sensitivity while avoiding artifacts induced by large drive biases. Conventional PFM often relies on high voltages to overcome optical detection noise, leading to various non-ideal effects including electrostatic crosstalk, Joule heating, and tip-induced switching. To mitigate this situation, we introduce interferometrically detected, resonance-enhanced dual AC resonance tracking (iDART), which combines femtometer-scale displacement sensitivity of quadrature phase differential interferometry with contact resonance amplification. Through this combination, iDART achieves 10x or greater signal-to-noise improvement over current state of the art PFM approaches including both single frequency interferometric PFM or conventional, resonance enhanced PFM using optical beam detection. In this work, we demonstrate a >10x improvement of imaging sensitivity on PZT and Y-HfO. Switching spectroscopy shows similar improvements, where further demonstrates reliable hysteresis loops at small biases, mitigating nonlinearities and device failures that can occur at higher excitation amplitudes. These results position iDART as a powerful approach for probing conventional ferroelectrics with extremely high signal to noise down to weak piezoelectric systems, extending functional imaging capabilities to thin films, 2D ferroelectrics, beyond-CMOS technologies and bio-materials.
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All authors J. Bemis, F. Wunderwald, U. Schroeder, X. Xu, A. Gruverman, R. Proksch

Materials Science · Cross-listed from physics.comp-ph

Machine-learned domain partitioning for computationally efficient coupling of continuum and particle simulations of membrane fabrication

Matthias Busch, Gregor Häfner, Jiayu Xie et al. (+4 more)

All simulation approaches eventually face limits in computational scalability when applied to large spatiotemporal domains. This challenge becomes especially apparent in molecular-level particle simulations, where high spatial and temporal resolution leads to rapidly increasing computational demands. To overcome these limitations, hybrid methods that combine simulations with different levels of resolution offer a promising solution. In this context, we present a machine learning-based decision model that dynamically selects between simulation methods at runtime. The model is built around a Multilayer perceptron (MLP) that predicts the expected discrepancy between particle and continuum simulation results, enabling the localized use of high-fidelity particle simulations only where they are expected to add value. This concurrent approach is applied to the simulation of membrane fabrication processes, where a particle simulation is coupled with a continuum model. This article describes the architecture of the decision model and its integration into the simulation workflow, enabling efficient, scalable, and adaptive multiscale simulations.
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All authors Matthias Busch, Gregor Häfner, Jiayu Xie, Marius Tacke, Marcus Müller, Christian J. Cyron, Roland C. Aydin

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Broadband Thermal Noise Correlations Induced by Measurement Back-Action

Jiaxing Ma, Thomas J. Clark, Vincent Dumont et al. (+1 more)

Modern mechanical sensors increasingly measure motion with precision sufficient to resolve the fundamental thermal noise floor over a broad band. Compared to traditional sensors – achieving this limit only near resonance – this capability provides massive gains in acquisition rates along with access to otherwise obscured transient signals. However, these stronger measurements of motion are naturally accompanied by increased back-action. Here we show how resolving the broadband thermal noise spectrum reveals back-action-induced correlations in the noise from many mechanical modes, even those well-separated in frequency. As a result, the observed spectra can deviate significantly from predictions of the usual single-mode and (uncorrelated) multimode models over the broad band, notably even at the mechanical resonance peaks. This highlights that these effects must be considered in all systems exhibiting measurement back-action, regardless of whether the resonances are spectrally isolated or the readout noise is high enough that the noise peaks appear consistent with simpler models. Additionally, these correlations advantageously allow the thermal noise spectrum to reach a minimum – equivalent to that of a single mode – in a band far from the resonance peak, where the mechanical susceptibility is comparatively stable against frequency noise.
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All authors Jiaxing Ma, Thomas J. Clark, Vincent Dumont, Jack C. Sankey