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Physics Condensed Matter

cond-mat Watch Condensed Matter

Monday 17 August

Statistical Mechanics

Rare-event sampling for stochastic dynamics in network systems using cluster updates

Jiazheng Sun, James Moody and Thomas Barthel

Understanding the stochastic evolution in complex networks is a central challenge across physics, biology, engineering, social science, and finance. The most consequential macroscopic events, like cascading failures in communication networks, widespread epidemic outbreaks, and rapid shifts in societal opinions, often emerge from a confluence of rare, localized stochastic processes and need to pass certain bottlenecks. Standard forward-time simulation algorithms like the Gillespie method are inefficient for the investigation of such phenomena due to catastrophic rejection rates. Advanced rare-event techniques like splitting methods and transition-path sampling often suffer from kinetic trapping, path degeneracy, genealogical correlations, or critical slowing down when applied to complex heterogeneous networks. We propose to overcome this challenge by establishing a novel technique called conditional-path Monte Carlo (CPMC), inspired by loop algorithms from equilibrium condensed-matter physics. By employing non-local updates on spacetime clusters without rejections, CPMC generates a Markov chain of trajectories that all strictly respect the targeted macroscopic boundary conditions like the occurrence of a massive network failure. We demonstrate the framework's potential by performing a simple risk factor analysis for rare large-scale epidemic outbreaks in SIS dynamics on kinship networks.
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Materials Science

Spin-pump-induced spin transport demonstration in a photoconductive PTCDA molecular thin film with a transparent spin current detector

Yuri Matsukawa and Eiji Shikoh

We demonstrate spin-pump-induced spin transport in a photoconductive PTCDA (3,4,9,10-perylene-teracarboxylic dianhydride) molecular thin film with a transparent ITO (In2O3 + SnO2) film as a spin current detector. In a tri-layer stacking structure sample composed of ITO/PTCDA/Ni80Fe20, pure spin current is generated in the PTCDA layer by using the spin pumping driven by the ferromagnetic resonance of the Ni80Fe20 layer. The generated spin current is absorbed into the ITO layer, converted to a charge current due to the inverse spin-Hall effect of the ITO layer, and detected as an electromotive force via the ITO resistance. Also, the light irradiation effect on spin transport in PTCDA films is investigated.
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Soft Condensed Matter

Finite strain homogenization of periodic rod networks with application to semi-flexible biopolymers

Vinayak, Prashant K. Purohit and Ajeet Kumar

In this work, we adopt a finite strain computational homogenization approach to characterize the response of semi-flexible biopolymer networks modeled as idealized 8- and 14-chain periodic networks. We use the geometrically exact special Cosserat rod theory to model the microscale fibers forming these 8- and 14-chain networks. This allows us to capture arbitrarily large microscale deformations. Both macroscopic strain- and stress-driven homogenization are performed to study the macroscopic uniaxial tension, compression and simple shear responses. Several phenomena unique to biopolymer networks are recovered such as strain-stiffening and volume shrinkage under uniaxial tension, softening under compression and reverse Poynting effect under simple shear. We find that nonlinearity and non-affine deformation at microscale, especially bending and buckling of microscale fibers, plays an important role in these phenomena. We obtain the postbuckled solutions of the homogenization problem using a nonlinear, imperfection-free path following approach and also check for their stability. We further compare our homogenization results with experimental data for uniaxial tension and compression of biofilament networks and find good agreement. When the fibers are replaced by helical rods in the 8-chain unit cell, we are also able to capture the enlarged stretching behaviour as shown in recently fabricated compliant metastructures.
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Materials Science

First-Principles Prediction of Phonon-Mediated Infrared Optical Properties of WO$_3$ Polymorphs

Sreerag Sundaram and Karthik Sasihithlu

Many crystals exhibit polymorphism, undergoing atomic rearrangements that result in unit cells belonging to different symmetry groups. These structural changes directly affect lattice vibration modes and consequently influence their mid-infrared optical properties. In this study, we use tungsten trioxide (WO$_3$) as a representative system, owing to its multiple temperature-dependent phases, to study the impact of polymorphism on mid-infrared optical behaviour. Using a fully first-principles approach, we investigate three phases of WO$_3$ and evaluate their mid-infrared optical properties. Significant differences are observed among the three crystallographic phases, demonstrating the potential of this methodology as a predictive tool for materials discovery and targeted design.
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Mesoscale and Nanoscale Physics

Helical Magnon Frequency Comb in Synthetic Antiferromagnetic Skyrmion Lattices

Liu Xuejuan, Zheng Xingen, Li Zhixiong et al. (+5 more)

Synthetic antiferromagnetic skyrmion lattices (SAF-SkLs), consisting of two ferromagnetic SkLs coupled antiferromagnetically with compensated magnetization, provide a promising platform for robust nonlinear magnonics. Here, we investigate helical magnon frequency comb (HMFC) generation in a SAF-SkL by combining analytical modeling with micromagnetic simulations. We show that nonlinear coupling between helical magnon edge states and the skyrmion gyration produces frequency combs with pronounced edge localization. The HMFC exhibits strong enhancement exclusively when the driving frequency lies within the helical edge-state band, whereas the interior response remains negligible. This frequency selectivity confirms the essential role of helical edge modes in localized nonlinear frequency conversion. We further demonstrate that the interlayer antiferromagnetic coupling reconstructs the magnon spectrum, thereby tuning the comb spacing and the number of comb teeth while also redistributing modal energy. Our results establish SAF-SkLs as a tunable platform for edge-localized HMFCs and suggest a route toward robust coherent magnonic signal processing.
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All authors Liu Xuejuan, Zheng Xingen, Li Zhixiong, Li Xiaoguang, Zhou Cangtao, Li Hui, Sun Haipeng, Yan Peng

Superconductivity

Superconducting $T_\mathrm{c}$ up to 20.6 K in bulk YSi$_2$ and YSi$_2$/Si superlattices due to chemical flattening

Ding-qing Li, Chong Tian, Juan Du et al. (+5 more)

Currently, the fundamental building blocks of leading quantum computers are Josephson junctions, whose core is usually the superconducting Al on Si wafers. However, the transition temperature $T_\mathrm{c}$ of bulk Al ($\sim1.1$ K) is below the boiling point of liquid helium ($\sim4.2$ K), which is one of the challenges to its widespread application. Here, we propose a Si-matched AlB$_2$-type superconductor YSi$_2$ as a promising alternative to Al. The solution of anisotropic (isotropic) Migdal-Eliashberg equation without (with) anharmonicity gives $T_\mathrm{c}\sim20.6$ K ($17.2$ K), which is at the highest level in silicides. Its excellent superconductivity can be attributed mainly to the Si honeycombs, which become plane here due to the 'chemical flattening' effects of the Y atoms instead of being buckled in most silicides. We tested its thermodynamical, kinetic, dynamical, and mechanical stability by first-principles calculations. Particularly, the negative elastic stiffness constant $C_{66}$ calculated by usual methods turns positive even without the zero-point energy once the Si honeycombs are compressed below a threshold. This strain can also make its calculated lattice constants agree with the experimental ones. We propose structures to realize this strain, i.e., YSi$_2$(0001)/Si(111) superlattices, which can also strengthen the overall stability of YSi$_2$ while maintaining its $T_\mathrm{c}$ above $7.0$ K.
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All authors Ding-qing Li, Chong Tian, Juan Du, Jun-jie Shi, Pei-song He, Deng-hui Xu, Hong-xia Zhong, Yao-hui Zhu

Mesoscale and Nanoscale Physics

Chiral Damping-Induced Chirality Switching and Control of Domain Walls in Antiferromagnets

Collins Ashu Akosa, Mu-Kun Lee, Aurélien Manchon et al. (+1 more)

We investigate the impact of chiral damping (CD) on current-driven domain-wall (DW) dynamics in antiferromagnets (AFMs). Asymmetric CD between sublattices generates off-diagonal components in the DW mass tensor, thereby coupling translational and rotational modes. When CD is modulated by an ac gate voltage via the Rashba spin-orbit interaction (RSOI), symmetric and asymmetric contributions induce oscillations in the DW velocity and tilt angle, respectively. A perturbative analysis yields explicit expressions for the oscillation amplitudes, in quantitative agreement with numerical simulations. Remarkably, even in the absence of Dzyaloshinskii-Moriya interaction (DMI), asymmetric CD enables chirality switching between Néel- and Bloch-type DWs. Finally, by exploiting the relativistic Lorentz contraction of the DW width at high driving currents, we propose an experimentally viable protocol to qualitatively and quantitatively extract the CD contribution. These results establish clear experimental signatures of CD in antiferromagnetic DW dynamics and demonstrate its potential as a control parameter for magnetic textures.
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All authors Collins Ashu Akosa, Mu-Kun Lee, Aurélien Manchon, Masahito Mochizuki

Disordered Systems and Neural Networks · Cross-listed from physics.optics

In-situ adjoint protocols for nonlinear PT-symmetric self-optimizing machines

Zheming Li, Lucas J. Fernández-Alcázar, Zin Lin et al. (+1 more)

Adjoint methods provide a powerful route for gradient-based optimization, but their physical implementation is obstructed in generic nonlinear systems because the adjoint dynamics requires backward-time evolution, Jacobian transposition, and terminal-value constraints. Here we show that nonlinear parity-time ($\mathcal{PT}$)-symmetric systems overcome this obstruction. Using a class of nonlinear non-Hermitian resonator networks, we establish symmetry relations that map the formal adjoint dynamics onto experimentally accessible forward-time evolutions supplemented by controlled injections. This construction enables exact in-situ evaluation of adjoint gradients without requiring explicit backward propagation or matrix transposition. We demonstrate the approach in nonlinear $\mathcal{PT}$-symmetric resonator chains, where the resulting optimization protocol autonomously discovers parameter configurations that realize prescribed spatio-temporal functionalities, including uniform energy redistribution and targeted wave transport at predefined time windows. Our results identify $\mathcal{PT}$ symmetry as a resource for implementing computational sensitivities within physical systems and establish a route toward self-optimizing nonlinear machines.
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All authors Zheming Li, Lucas J. Fernández-Alcázar, Zin Lin, Tsampikos Kottos

Statistical Mechanics · Cross-listed from nucl-th

Deep-learning classification of physically admissible nuclear-matter equations of state

Ahmed Abuali, Micheal Kahangirwe, Francesco Di Clemente et al. (+3 more)

Thermodynamic stability and causality impose fundamental constraints on the equation of state (EoS) of nuclear matter. Verifying these constraints conventionally requires calculating quantities such as the specific heat, baryon-number susceptibility, and speed of sound, which can become computationally expensive when many candidate EoSs must be examined. We investigate whether the normalized pressure surface, $Q(T,\mu_B)=P(T,\mu_B)/T^4$, alone contains sufficient information to determine the physical admissibility of an EoS. We develop a supervised convolutional neural network (CNN) that uses only this pressure representation to classify EoSs as physically admissible or inadmissible. The network is provided with training labels obtained from direct thermodynmaic stability and causality check and its does not get any information about the parameters of the underlying EoS framework. For EoSs generated within an Ising-mapping framework, the model achieves $97.65%$ accuracy on unseen test data. Applied independently to EoSs from a distinct holographic framework, it achieves perfect classification of the test set. These results show that pressure surfaces contain geometric signatures of thermodynamic stability and causality violations that can be learned directly by a CNN. Because the classifier relies only on the pressure surface, it avoids evaluating higher-order thermodynamic observables during inference and is largely independent of the EoS-generation framework. When the pressure surface is supplied as a two-dimensional array, the machine-learning validation is approximately 20 times faster than direct validation. Our results establish a fast, framework-independent approach for identifying physically admissible EoSs directly from their pressure surfaces.
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All authors Ahmed Abuali, Micheal Kahangirwe, Francesco Di Clemente, Vianney E Diaz-Barraza, Jorge A Munoz, Claudia Ratti

Materials Science · Cross-listed from physics.optics

Transport-defined photodetection through electrically selectable nonequilibrium carrier transport

Jiaxuan Cai, Yan Xie, Ning Yang et al. (+9 more)

Broadband optical fields can change in both intensity and spectral distribution, but a fixed-response detector maps this evolving information onto a single electrical signal. Here we demonstrate transport-defined photodetection, in which electrical bias selects how photoexcited carriers are redistributed, escape and are collected, creating complementary response functions within one shared active region. In a GaAs/AlGaAs semiconductor ratchet, light-driven ratchet transport defines the response at 0 V, whereas the spectral evolution at -2 V is consistent with field-assisted hot-carrier transport. The overlapping states span a measured spectral range of 0.4-94.5 {\mu}m at 5 K, provide state-dependent calculated detection floors and support joint infrared operation at 30 K. Direct optical beat notes at 7.432 GHz in the mid-infrared and 17.103 GHz in the terahertz demonstrate optical-to-electrical conversion. Their common-path outputs recover an imposed spatial temperature gradient and the transient field-of-view-integrated effective radiation temperature of laser-excited graphite. These results establish post-photoexcitation transport as a function-defining design variable for semiconductor photodetectors, complementing structure-defined, field-tuned and optically encoded approaches to reconfigurable photodetection.
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All authors Jiaxuan Cai, Yan Xie, Ning Yang, Weidong Chu, Peng Bai, Lianhe Li, Edmund H. Linfield, Hanbing Wang, Meng Chen, Guanchen Li, Yingxin Wang, Ziran Zhao

Strongly Correlated Electrons

Transport-Noise Witnesses of Electronic Multipartite Entanglement

Shuhan Ding, Prakash Sharma, Zecheng Shen et al. (+3 more)

Entanglement among particles is a defining feature of strongly correlated quantum materials, distinguishing them from conventional metals and semiconductors. The ability to certify intrinsic entanglement among interacting electrons in solid-state materials is important not only for classifying quantum states of matter, but also for developing material-based quantum technologies. Here, we introduce a transport-based protocol for witnessing multipartite entangled electronic states, based on the equilibrium noise spectrum as an experimentally accessible observable. The appropriately integrated, symmetrized, and projected current noise obeys an upper bound that can be derived from microscopic model parameters and is invariant with respect to the choice of electronic basis. We benchmark this framework in several paradigmatic systems, including twisted bilayer graphene, twisted bilayer MoTe$_2$, and Hubbard models, certifying entanglement in the fractional Chern insulating state. The method extends recently developed scattering-based entanglement witnesses to ultralow-temperature materials, where conventional spectroscopic probes are inaccessible but candidate entangled states are expected to arise.
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All authors Shuhan Ding, Prakash Sharma, Zecheng Shen, Jiang-Xiazi Lin, Sergei Urazhdin, Yao Wang

Materials Science

Beyond Local Berry Geometry: A First-Principles Finite-Momentum Theory of Electronic Position

M. S. Si, Y. Q. Li and G. P. Zhang

Electronic position controls how a crystal polarizes and responds to an external field. In crystals, it is usually described through local changes of electronic states in momentum space. This Berry framework has reshaped modern solid-state physics, but strong fields drive electrons across a finite momentum range, where coherence between different momenta becomes part of the response. Here we establish a first-principles theory of electronic position at finite momentum that retains this missing information. We show that unequal-momentum coherence can cancel under spatial averaging and still produce polarization, forming a coherence dipole. We obtain the matrix directly from material wave functions, without model bands or fitted transition elements. In Si, the finite-momentum geometry sets a material momentum scale. Comparing this scale with the momentum change driven by the field predicts when finite-momentum physics becomes active. Crossing the scale strongly reorganizes the fifth and higher harmonics, showing that momentum-space geometry, rather than emitted photon energy alone, controls the nonlinear response. HHG is the first demonstration, but the theory applies whenever driven electrons explore a finite momentum range. It therefore extends quantum geometry beyond the local Berry limit and provides a general basis for predicting field-driven phenomena in real materials.
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Sunday 16 August

Mesoscale and Nanoscale Physics

Electrically Switchable Spintronics in a Multiferroic Altermagnet

Martin Latorre, Sebastian Allende and Alvaro S. Nunez

We introduce a minimal model of a two-dimensional lattice that, upon spontaneous symmetry breaking, simultaneously develops altermagnetic order, a finite electric polarization, and a spin-polarized transport response, all of which are controlled by an external electric field. By coupling a dimerized altermagnet to an external electric field, we show that the three order parameters are not merely compatible but dynamically entangled, so that switching one (for instance, reversing the polarization with an electric field) necessarily reconfigures the other two. We show that this model offers a clear physical blueprint for designing next-generation spintronic logic and pure spin current memdevices that merge the ultrafast, stray-field-free advantages of compensated magnets with the low-power switching architectures of ferroelectrics.
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Materials Science

Synthesizing like a chemist: an iterative, feedback-driven loop for materials discovery

Fang Sheng, Steven B. Torrisi, Amanda Volk et al. (+4 more)

Most computationally predicted materials are never synthesized because conventional synthesis optimization is slow, expertise-dependent, and iterative. Here we present a closed-loop framework that automates this expert workflow by placing human tacit knowledge in the loop through a large language model (LLM) that distills synthesis knowledge from the literature, high-throughput hyperspectral imaging for rapid film evaluation, and multi-objective Bayesian optimization guided by experimental feedback. In a paired optimization campaign, LLM-assisted initialization produced more Pareto-optimal samples and higher hypervolume than a Latin hypercube sampling baseline at matched trial counts, and this advantage persisted throughout iterative optimization. We demonstrate the framework by synthesizing the previously unreported perovskite-inspired compound Rb3BiI6 as thin films and validating the optimized films by optical bandgap analysis and X-ray diffraction. The framework transforms synthesis prediction from single-shot recommendation to iterative learning, providing a generalizable strategy to accelerate automated and fully autonomous experimental materials discovery.
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All authors Fang Sheng, Steven B. Torrisi, Amanda Volk, Kevin Tran, Koki Nakano, Brian W. Anthony, Tonio Buonassisi

Superconductivity

Identification and electrothermal modeling of persistent current switch operating regimes in a Siemens MRI magnet using external electrical measurements

Volodymyr Pupkov

The persistent current switch (PCS) closes the superconducting loop of an MRI magnet. During ramping it is commonly treated as a binary element: with the heater on, the PCS branch is assumed effectively open; after heater turn-off, it is assumed superconducting. Field measurements with an MPS2 service power supply (Digit Systems) on a Siemens MAGNETOM Avanto show that the PCS remains electrically active and that its resistive state can persist after heater turn-off through Joule self-heating. Dedicated maneuvers identified two resistive regimes. With the heater on, the low-voltage resistance is nearly constant; after heater turn-off, self-heating produces a power-law voltage dependence. Both are described by a single effective electrothermal relation, $R_{sw}=C\,(P_h h+V_{node}^2/R_{sw})^a$, where $h$ is the recorded heater state, spanning a 690-fold resistance range. Final-hold data from 17 Siemens magnet sessions confirmed the voltage dependence of effective PCS resistance. Since branch-current relaxation follows $\tau=L/R_{sw}$, the required hold time depends on switch state rather than a fixed delay; the median margin after source settling was $3.6\,\tau$. The intersection of the PCS characteristic with the external-circuit load line defines the boundary of self-sustained resistive operation. For Avanto, the predicted 0.062 V threshold lay between superconducting recovery at 0.06 V and resistive-state persistence at 0.07 V, and retrospectively classified all 24 archived segments correctly. Including both PCS resistive regimes in the dynamic model reproduced the observed current redistribution: RMSE decreased from 1.449 to 0.154 A, a factor of 9.4. This improvement required explicit representation of heater state.
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Materials Science

Crystal-structure design by agentic AI in a language of motifs

Dinh-Khiet Le, Minh-Quyet Ha, Hong-Phuc Vu-Dinh et al. (+3 more)

Data-driven materials discovery interpolates more reliably than it extrapolates and seldom reaches new structure types. We present MatEvolve, an agentic-AI framework designing crystals, proposing each candidate with a stated rationale and testing it. The agent reasons in an interpretable language of motifs, writing each crystal as a motif profile that describes the recurring geometric patterns—the motifs—composing it. The motif profile serves not merely as a description of a material but as the medium for material design: the agent edits the profile and constructs a crystal from the modified one, and the most promising candidates are validated by first-principles calculation. Applied to the design of rare-earth-lean permanent magnets, MatEvolve—built on the state-of-the-art language model Claude Fable~5 without fine-tuning—reaches new structural prototypes more than three times as often as generative models under an equal validation budget, at a comparable on-target-magnet rate. Beyond design, analysing the discovered crystals' human-readable profiles reveals structure–property relationships.
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All authors Dinh-Khiet Le, Minh-Quyet Ha, Hong-Phuc Vu-Dinh, Takashi Miyake, Hiori Kino, Hieu-Chi Dam

Statistical Mechanics

Dynamic critical exponent of the Yang–Lee edge singularity at three loops

Loran Ts. Adzhemyan, Diana A. Davletbaeva, Daniil A. Evdokimov et al. (+1 more)

We compute the dynamic critical exponent $z$ of the Yang–Lee edge singularity in relaxational dynamics using perturbative renormalization-group methods to the three-loop order. The calculation combines diagram reduction, analytic two-loop evaluation via parametric integration with hyperlogarithms, and numerical evaluation of three-loop integrals using the Sector Decomposition method. The perturbative series obtained is resummed using Padé and Padé-Borel-Leroy methods to produce estimates of $z$ in various spatial dimensions. The resulting values are consistent with previous perturbative and functional renormalization-group calculations.
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All authors Loran Ts. Adzhemyan, Diana A. Davletbaeva, Daniil A. Evdokimov, Mikhail V. Kompaniets

Materials Science

Rare-earth chalcogenide perovskites: A promising class of materials for optoelectronic applications

Surajit Adhikari and Priya Johari

Rare-earth chalcogenide perovskites have attracted significant attention for optoelectronic applications due to their nontoxic composition, robust phase stability, and excellent optoelectronic properties. However, their excitonic and polaronic properties remain largely unexplored due to the high computational cost of accurate theoretical treatments. In this work, we present a comprehensive first-principles investigation of excitonic dynamics and polaronic effects in a series of III-III rare-earth chalcogenide perovskites ABX$_{3}$ (A = Y, La; B = Sc, Y; X = S, Se), along with their structural stability and optoelectronic properties, using state-of-the-art density functional theory in conjunction with many-body perturbation theory within the G$_{0}$W$_{0}$ and Bethe-Salpeter equation (BSE) frameworks. All investigated compounds satisfy the dynamical and mechanical stability criteria. They exhibit quasiparticle band gaps in the range of 2.75$-$4.47 eV, and the BSE calculations reveal strong optical absorption spanning the visible to ultraviolet regions. The computed excitonic properties indicate intermediate-to-large exciton binding energies (0.148$-$0.517 eV), moderately localized excitons, and strong electron-hole wavefunction overlap, indicative of favorable radiative recombination characteristics and enhanced light-matter interaction. Furthermore, analysis based on the Fröhlich model demonstrates intermediate-to-strong carrier-phonon coupling, with electron-phonon interactions generally stronger than hole-phonon interactions. Overall, rare-earth chalcogenide perovskites ABX$_{3}$ exhibit a compelling combination of structural stability, tunable optoelectronic properties, pronounced excitonic effects, and favorable polaronic transport, positioning them as promising lead-free materials for next-generation optoelectronic devices, including light-emitting devices and photodetectors.
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Mesoscale and Nanoscale Physics

Morphology-Guided Deterministic Fabrication of Low-Noise High-Temperature Superconducting Quantum Interference Devices

Bingke Xiang, Wanjuan Tang, Shiqun Liu et al. (+9 more)

Reproducible bicrystal high-temperature superconducting quantum interference devices remain limited by local variability along the grain boundaries that form the Josephson junctions. Here, we develop a site-selective fabrication workflow in which atomic force microscopy maps the intended junction region before lithography, quantifies an apparent grain-boundary width, rejects pore-rich segments, and writes a nearby registration mark for site-specific pattern alignment. The apparent grain-boundary width provides a practical morphology metric, with narrower regions consistently yielding larger critical currents and characteristic voltages. Iterative optimization within this workflow further improves junction and device performance, reaching a liquid-nitrogen-temperature field-noise level of 40 fT Hz^(-1/2). This strategy turns local grain-boundary heterogeneity from an uncontrolled source of variability into a basis for site-selective fabrication, providing a route towards scalable manufacturing of low-noise HTS SQUIDs with high uniformity.
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All authors Bingke Xiang, Wanjuan Tang, Shiqun Liu, Lingtong Hou, Geming Zhang, Yibo Wang, Ruonan Wang, Zhiqiang Cao, Jiaqi Wei, Xueshen Wang, Xueying Zhang, Xiaoyang Lin

Materials Science

Strain-stabilized altermagnetism and conductivity anisotropy in FeSb2

Masoumeh Davoudiniya, Alyssa M. Kennedy, Amy Y. Liu et al. (+1 more)

We show that FeSb2 experiences a transition from a conventional antiferromagnet to an altermagnet when tensile strain is applied. In the altermagnetic phase, the lifted Kramers degeneracy results in spin splitting up to ~0.2eV near the Fermi level even without spin-orbit coupling. The transition to the altermagnetic phase is accompanied by a dramatic change in the Fermi-surface geometry, which leads to a uniaxial conductivity anisotropy up to ~60%, much greater than those observed in typical ferromagnetic metals. Using density-functional theory and Wannier interpolated Fermi surfaces, we show that this magnetotransport behavior may function as an experimental indicator of the transition to the altermagnetic phase. These findings highlight FeSb2 as a versatile, strain-tunable platform for exploring and utilizing altermagnetic transport phenomena for spintronic devices.
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All authors Masoumeh Davoudiniya, Alyssa M. Kennedy, Amy Y. Liu, Gen Yin

Strongly Correlated Electrons · Cross-listed from quant-ph

Topologically Protected Learning from Exceptional Point Braiding: Toward Braid Programming

M.N. Jipdi, C. Avomo Mba, A. B. Moubissi et al. (+2 more)

We present a framework for topological learning based on exceptional point (EP) braiding in a non-Hermitian Bogoliubov-de Gennes Hamiltonian. A closed algebraic equation for the EP super-surface is derived; through momentum quantisation in finite systems, it predicts the exact number and parameter positions of all EPs in real space, irrespective of system size. The EP topology is characterised by two quantised invariants the state-swap fidelity and the normalised Berry phase which cannot both be zero for a topological EP. A complete topological map shows that all EPs lie within a specefic region. Adiabatic encirclements confirm robust state swapping and yield a universal set of braid gates, including Pauli-X, Pauli-Y, Pauli-Z, a Hadamard-like gate, the T-gate, and a SWAP operation, with the special case where a is 0, providing additional phase gates. Building on these generators, we reformulate learning as braid programming a discrete search over the braid group that replaces gradient descent on continuous weights with combinatorial optimisation. A proof-of-concept genetic search successfully discovers short braid words that reproduce the standard Hadamard gate and the H.Z gate with perfect fidelity. This paradigm offers inherent noise immunity, catastrophic-forgetting prevention through compositional concatenation, and guaranteed generalisation by mathematical construction, establishing EP braiding as a promising substrate for robust, interpretable, and topologically protected neuromorphic computation.
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All authors M.N. Jipdi, C. Avomo Mba, A. B. Moubissi, L.C. Fai, M.E. Ateuafack

Strongly Correlated Electrons

Topological Altermagnetic Insulators

Jasmin Bedow, Nitin Kaushal and Marcel Franz

We study the emergence of altermagnetic topological phases stabilized by Ising spin-orbit coupling in a prototypical Lieb lattice model of a correlated altermagnet. Treating the electron interactions within the Hartree-Fock and the exact diagonalization techniques, we establish the co-existence of a quantum spin Hall effect with altermagnetic spin order over a wide region of the parameter space for average electron densities of 2 and 4 per unit cell. We explore how the magnetic structure along edges influences the electronic behavior of the associated topological edge modes, demonstrating their robustness against inversion-symmetry breaking terms.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Longitudinal-Field-Driven Transition in a non-integrable Non-Hermitian Transverse-Field Ising Chain via RBMs

M.E. Ateuafack, M.R. Kamsap, J.T. Diffo et al. (+2 more)

We investigate the ground-state properties and quantum critical behavior of a non-Hermitian transverse-field Ising chain subjected to longitudinal and complex transverse magnetic fields. To address this interacting many-body problem, we employ real-valued neural quantum states based on Restricted Boltzmann Machines (RBMs), optimized using Variational Monte Carlo (VMC) sampling. Spectral analysis of finite chains reveals exceptional points associated with spontaneous parity-time (PT) symmetry breaking. A real-valued RBM framework is developed to reconstruct the ground-state eigenstates of the non-Hermitian Hamiltonian. Benchmark comparisons with exact diagonalization demonstrate that the RBM approach accurately reproduces the ground-state energy, magnetization, and spin-spin correlations. Extending the analysis to larger system sizes, we identify a non-Hermitian quantum phase transition characterized by PT-symmetry breaking and the emergence of magnetic order. Our results establish real-valued neural quantum states as an efficient and scalable framework for investigating critical phenomena in interacting non-Hermitian quantum systems.
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All authors M.E. Ateuafack, M.R. Kamsap, J.T. Diffo, L.C. Fai, M.N. Jipdi

Strongly Correlated Electrons

Linear response functions from inhomogeneous dynamical mean-field theory

Don Rolih and Fabian B. Kugler

We present a method for calculating static lattice susceptibilities with inhomogeneous dynamical mean-field theory. The method utilizes the response of the system to an external field and thereby circumvents two-particle vertex functions. We demonstrate the success of our approach for the magnetic susceptibility of the square-lattice Hubbard model using the numerical renormalization group as an impurity solver and show that it compares well with the results obtained using the standard vertex approach. As it avoids vertex functions and is compatible with virtually any impurity solver, our method is able to reach low temperatures that are hard to access with other methods.
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Mesoscale and Nanoscale Physics

The Hodge structure of Berry-phase transport: topology, geometry, and noise

Zhi-Wei Wang and Samuel L. Braunstein

We show that the Hodge-de Rham decomposition of the Berry curvature organises the transport of a Bloch band and its fluctuations within a single geometric structure. Splitting the curvature into $L^2$-orthogonal harmonic, exact, and co-exact sectors yields a dictionary for both moments of the current. In the mean response the harmonic sector carries the topological anomalous-Hall conductivity, the exact sector the Fermi-surface geometry and the antisymmetric Berry-curvature dipole of polar metals, and, in three dimensions, the co-exact sector the chiral anomaly, quantised by the Weyl-node charges. In the fluctuations, described by a particle-conserving stochastic Boltzmann equation constrained by the fluctuation-dissipation theorem (FDT), the harmonic sector is silent, so topological transport is noiseless, while the field-driven noise is sourced by the geometric sectors (solely the exact sector in two dimensions); current-noise spectroscopy therefore separates global band topology from local band geometry. We prove that the harmonic null-space protection is dimension-independent, and we settle the remaining sector: the co-exact (monopole) sector carries no conservation law and, under the thermal sampling measure, mixes with the exact sector at $\mathcal{O}(1)$, so it furnishes no clean noise observable. The separation the noise provides is therefore two-way, topology versus geometry, in both two and three dimensions.
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Soft Condensed Matter · Cross-listed from physics.chem-ph

Gas-generating reactive flows in bicontinuous catalyst support structures

J.M.P. Beunen and J. Harting

A major challenge in the field of heterogeneous catalysis is selecting an optimal catalyst support structure. Commercially available structures can be easily manufactured at scale, but their stochastic nature makes their chemical and transport properties suboptimal. This is particularly relevant for gas-generation reactions, where non-uniformity of a porous structure leads to bubble trapping. Such trapping impedes the flow of reactants to catalyst sites, leading to conversion inefficiencies. Previous experimental work demonstrated that spinodally-derived architectures, in particular bicontinuous interfacially jammed emulsion gels (bijels), can alleviate these issues and deliver superior performance. However, to the best of our knowledge, numerical studies to optimize the operating conditions for such a morphology have not been performed yet. In this work, we aim to close this gap using color-gradient lattice Boltzmann simulations of reactive flows with a novel central moments collision operator. We develop an analytical model to predict catalyst performance based on our simulation data. Our findings show that this type of morphology can achieve very high conversion efficiencies. Moreover, we demonstrate that its catalyst performance can be optimized using superhydrophilic surface coatings.
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Materials Science

ALKEMIE Agent: an autonomous platform for computational materials design

Hongfu Huang, Yuzhe Li, Ao Xu et al. (+14 more)

Despite the powerful multi-scale modeling methods and high-throughput infrastructures established in the materials community, real material computation workflows remain fragmented and heavily manual, requiring researchers to constantly bridge software tools, data analysis, and intermediate decisions. This growing gap between methodological capability and practical execution highlights the need for a new kind of autonomous computational framework, one that can coordinate tools, knowledge, and workflows in a more unified and adaptive way. Here, we introduce ALKEMIE Agent, an agentic platform in which retrieval-augmented generation, a materials-computation knowledge base, registered skills, database-supported provenance, AI-assisted structure modeling, bounded task execution, tool-calling iteration, and error-diagnostic assistance are integrated within a traceable control loop. The capabilities of ALKEMIE Agent are demonstrated through applications including materials recommendation, structure modeling, phonon calculations, machine-learned interatomic potential training, LAMMPS simulations, Ab Initio Monte Carlo (AIMC) sampling, and active-learning-based materials screening. Finally, we outline the future directions and challenges for the development of agentic platforms for computational materials design.
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All authors Hongfu Huang, Yuzhe Li, Ao Xu, Bo Liu, Changrui Wang, Kan Tang, Ning Yang, Shengxian Liu, Hanyu Liu, Pengpeng Zhang, Linggang Zhu, Fengkai Liu, Yichen Lu, Tong Zhao, Naihua Miao, Jian Zhou, Zhimei Sun

Materials Science

Design of altermagnetism in oxide superlattices exploiting interface effects and quantum confinement

Subhadeep Bandyopadhyay and Rossitza Pentcheva

The discovery of altermagnetism has initiated intensive research and opened new avenues for spin- tronic and transport applications. While current efforts are mostly focused on bulk materials which are typically insulating, here we propose design strategies to achieve a combination of altermag- netism and metallicity in oxide superlattices by exploiting symmetry breaking, electrostatic doping and confinement. While bulk SrCrO3 does not exhibit altermagnetism due to compensating effects between adjacent layers our density functional theory calculations with a Hubbard U parameter re- veal, that a single SrCrO3 layer confined in a (SrCrO3)1/(SrTiO3)1(001) superlattice (SL) exhibits a sizable non-relativistic spin splitting (NRSS) up to 350 meV with bulk d-wave nature due to the coexistence of orbital ordering and octahedral rotations (OORs). Since this system is insulating, we extend to SrCrO3/LaCrO3(001) SLs. In the (SrCrO3)4/(LaCrO3)4(001) SL the combination of a polar discontinuity at the interface and stronger OORs promotes metallic d-wave altermagnetism. The NRSS of up to 120 meV is contributed by the interfacial Cr d bands at the Fermi level with indications for a spin-selective Fermi surface nesting. These findings establish oxide superlattices as a promising platform to realize and explore altermagnetism for quantum transport and spintronic functionalities
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Quantum Gases · Cross-listed from nucl-th

Renormalization Group Analysis of Pairing Instabilities in Nuclear Fermi Liquids

Yang Xiao, Yixin Guo and Youngman Kim

A nuclear Fermi liquid exhibits competing pairing instabilities in different spin, isospin, and orbital channels. In a Fermi-surface renormalization group (RG) treatment, the channel that develops a pole first is determined not only by its tree-level attraction but also by its one-loop RG coefficient. We illustrate this mechanism in a minimal $S/P$-wave model. A spherical Fermi surface establishes the reference competition between the lowest even- and odd-parity interactions. Axial deformation changes the relevant Fermi-surface integrals and lifts the degeneracy between longitudinal and transverse $P$-wave components. In isospin-asymmetric matter, neutron–proton Fermi-momentum splitting restricts the simultaneous low-energy contribution of the two species and can terminate the $np$ running at finite threshold scales. Our calculations are intended as controlled one-loop RG illustrations rather than as quantitative nuclear-matter calculations. We show how the Fermi-surface geometry and composition can change the ordering of competing pairing instabilities.
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Superconductivity

Superconducting Hydride Mg2RhH6 Experimentally Achieved at Lower Pressure

Linjing Wu, Zelong Wang, Guiqi Liu et al. (+18 more)

Although tremendous progress has been made in recent years in the field of polyhydride superconductors, the realization of high critical temperature superconductivity still relies on formidable high pressures. Searching for superconducting hydrides at lower pressures is of particular importance. Here we report the first experimental synthesis of the Mg2RhH6, which achieves superconductivity under a significantly reduced pressure of 30 GPa. The synthesis of Mg2RhH6 proceeds via a two step process (1) preparation of the Mg2RhH5 precursor containing hydrogen atoms stabilized by covalent bonds, followed by (2) hydrogen supplementation resulting in the filling of electrons into anti bonding orbitals above 30 GPa, which was accompanied by the structural transition from RhH5 square pyramid to RhH6 octahedron. Superconductivity is achieved at 30 GPa with a Tc of 24 K, which is further enhanced to 29 K at 53 GPa, evidenced by a sharp drop of resistivity to zero and characteristic suppression of Tc under applied magnetic fields. Our experiments prove the Mg2RhH6 superconductor to be thermodynamically stable above 30 GPa, making it the first case exhibiting a Tc of approximately 30 K at a readily accessible pressure. This study pioneers a highly promising pathway for the rational design and discovery of high temperature superconductors within phonon mediated BCS framework.
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All authors Linjing Wu, Zelong Wang, Guiqi Liu, Jun Zhang, Yanfeng Ge, Yuanhao Su, Runteng Chen, Hongyu Liu, Wenmin Li, Sijia Zhang, Jingcheng Zhu, Jianfa Zhao, Zheng Deng, Shaomin Feng, Jing Song, Qingqing Liu, Xiang Li, Haozhe Liu, Panpan Kong, Xiancheng Wang, Changqing Jin