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Physics Condensed Matter Materials Science

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Thursday 23 July

Materials Science · Cross-listed from physics.optics

Phase singularity enabled polarization switchable analog spatial differentiation in an atomic MoS$_2$ planar Fabry-Pérot cavity

Zhonglin Li, Yingying Wang, Jiawei Kang et al. (+3 more)

Reconfigurable analog optical computing requires rapid and efficient switching between core mathematical operations, such as first- and second-order spatial differentiation. Here, we demonstrate a monolayer MoS$_2$ integrated a planar Fabry-Pérot (F-P) cavity that performs polarization switchable analog spatial differentiation under oblique incidence. By exploiting polarization dependent phase singularities, the device satisfies distinct optical transfer functions for different-order differentiation at the same operating condition. As a result, first-order and second-order derivatives of input images are experimentally realized by simply switching the incident polarization. These results establish the planar cavity as a compact reconfigurable spatial differentiator, whose computational order is controlled solely by light polarization. This approach provides a fast, convenient, and integration friendly strategy for tunable optical computing, and enables polarization switchable edge detection for image processing, with potential applications in real-time object recognition, feature extraction, and optical data compression.
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All authors Zhonglin Li, Yingying Wang, Jiawei Kang, Yangyang Zhang, Wenjun Liu, Zexiang Shen

Materials Science · Cross-listed from quant-ph

Picosecond-resolved entanglement distribution over an urban free-space channel

Alessandro Laneve, Fabrizio Cienzo, Santiago Gomez et al. (+18 more)

Time-evolving entangled states describe quantum particles whose correlations evolve in time according to a well-defined dynamics. Such states can be generated in a variety of physical systems and are promising resources for several quantum technologies, ranging from quantum clock synchronization to quantum communication. However, their full potential is currently limited by the fact that the entanglement dynamics often occur on timescales comparable to the achievable synchronization precision, especially in experiments aimed at distributing entanglement through noisy urban channels. In this context, accurate timing is not merely a technical detail, but a fundamental requirement for faithfully observing and exploiting the underlying quantum correlations. Here, we demonstrate the faithful distribution of a fast-evolving entangled state over a 270 m free-space channel connecting two buildings in the center of Rome. The developed system incorporates a synchronization device capable of achieving sub-50 ps timing accuracy between the two ends of the link while simultaneously supporting channel stabilization. Our results demonstrate that time-evolving entanglement can be reliably transmitted through a noisy urban free-space channel, representing an important benchmark toward long-distance free-space quantum communication and the future implementation of time-correlated entangled states in demanding scenarios such as satellite-based quantum networks.
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All authors Alessandro Laneve, Fabrizio Cienzo, Santiago Gomez, Paolo Barigelli, Philip Menz, Mattia Beccaceci, Giuseppe Ronco, Giorgia Grossi, Ievgen Brytavskyi, Thomas Oberleitner, Markus Wiener, Christian Weidinger, Tobias M. Krieger, Ailton Garcia Jr., Saimon Filipe Covre da Silva, Michele B. Rota, Nicolò Spagnolo, Henning Weier, Fabio Sciarrino, Armando Rastelli, Rinaldo Trotta

Materials Science

Tunnel magnetoresistance effect with a Cr-doped $\mathrm{RuO_{2}}(110)$ altermagnet

Katsuhiro Tanaka, Takuya Nomoto and Ryotaro Arita

Antiferromagnets can have a finite spin-polarization in the momentum space when their magnetic structure breaks the macroscopic time-reversal symmetry. This spin-polarization can produce a spin-polarized electric current even in antiferromagnets with vanishingly small net magnetizaton, which supports the antiferromagentic tunnel magnetoresistance (TMR) effect. In this paper, using first-principles calculations, we study the TMR effect with a doped altermagnet $\mathrm{Ru}_{1-x}\mathrm{Cr}_{x}\mathrm{O}_{2}$ with $(110)$ orientation, whose collinear antiferromagnetic structure breaks the time-reversal symmetry macroscopically. The momentum-dependent spin-polarization combined with the $(110)$ crystal orientation makes the electric current spin-polarized through bulk $\mathrm{Ru}_{1-x}\mathrm{Cr}_{x}\mathrm{O}_{2}(110)$. We further calculate the TMR effect in the $\mathrm{Ru}_{1-x}\mathrm{Cr}_{x}\mathrm{O}_{2}(110)/\mathrm{TiO_{2}}(110)/\mathrm{Ru}_{1-x}\mathrm{Cr}_{x}\mathrm{O}_{2}(110)$ tunnel junction and show that a finite TMR effect emerges. Based on the analysis of the tunneling transport, the TMR effect is attributed to the spin polarized tunneling transport with momentum dependence and the interfacial magnetic structures, as well as the spin-polarized electric current in a bulk form of $\mathrm{Ru}_{1-x}\mathrm{Cr}_{x}\mathrm{O}_{2}(110)$.
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Materials Science

Complete Raman Tensor Determination in Birefringent $\beta$-Ga$_2$O$_3$ by Single-Stage Hyperspectral Analysis of Polarization Angle-Resolved Raman Spectra

Hans Tornatzky, Jonas Rose, Moritz Meißner et al. (+5 more)

The low symmetry of the monoclinic phase of Ga$_2$O$_3$ leads to pronounced optical anisotropy and, consequently, to birefringence, which strongly affects the Raman response. Because Raman scattering is fundamentally sensitive to the polarizability of a material, this anisotropy must be carefully accounted for in order to extract quantitative information - an effort that has only recently been shown to be feasible in such media. Here, we report Raman measurements from all three principal crystal planes $(100)$, $(010)$, and $(001)$, as well as from the $(\overline{2}01)$-plane of a $\beta$-Ga$_2$O$_3$ single crystal. By combining polarization angle-resolved Raman spectroscopy (PARRS) with a newly developed fitting procedure and explicitly accounting for birefringence, we achieve full spectral separation and quantitatively determine the energies and relative Raman tensor elements of all 15 Raman-active modes.
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All authors Hans Tornatzky, Jonas Rose, Moritz Meißner, Benjamin M. Janzen, Zbigniew Galazka, Juan Sebastián Reparaz, Manfred E. Ramsteiner, Markus R. Wagner

Materials Science · Cross-listed from physics.optics

Monolithic Magneto-Optical Mach-Zehnder Isolator Using Laser-Annealed Iron Garnet on a Silicon Waveguide

Tomoya Sugita, Reona Motoji, Yuki Yoshihara et al. (+5 more)

Stable silicon photonic circuits require monolithically integrated optical isolators based on magneto-optical garnet. However, crystallizing the garnet by conventional furnace annealing exposes the entire chip to high temperature and degrades the silicon waveguides and the metal electrodes. Here we avoid this degradation by using local laser annealing in vacuum to crystallize cerium-substituted yttrium iron garnet (Ce:YIG), deposited by ion beam sputtering without a seed layer, directly within a silicon-based Mach-Zehnder interferometer. A 915 nm beam heats only the garnet region confined in micrometer-scale trenches, leaving the surrounding circuit and electrodes intact. The device achieves an isolation ratio of 13.6 dB at a wavelength of 1540 nm, corresponding to a Faraday rotation of 0.092$\deg$/$\mu$m, with an insertion loss of 20.4 dB and a propagation loss of 9.5 dB. Transmission electron microscopy reveals the crystallized Ce:YIG and a ~10 nm boundary region at the interface with the Si waveguide. These results demonstrate that thermally sensitive silicon photonic devices and magneto-optical thin films requiring high-temperature processing can be integrated by a high-throughput technique compatible with mass production.
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All authors Tomoya Sugita, Reona Motoji, Yuki Yoshihara, Dan Maeda, Hiroki Yamamoto, Hibiki Miyashita, Kazushi Ishiyama, Taichi Goto

Materials Science

Uni-XAS: Alignment-Driven Bidirectional Multimodal Learning for X-ray Absorption Spectroscopy

Suyang Zhong, Yuhao Zhao, Boying Huang et al. (+6 more)

X-ray absorption spectroscopy (XAS) is a key technique for probing local atomic environments, yet learning based modeling must bridge two heterogeneous modalities: 1D continuous spectra and 3D atomic structures. Existing approaches typically decouple forward spectrum prediction and inverse structure inference into separate regression tasks, hindering shared representation learning. Moreover, severe permutation ambiguity among identical atoms often limits inverse modeling to coarse structure descriptors rather than explicit 3D structure generation. In this work, we present Uni-XAS, a unified benchmark and learning framework that reframes bidirectional XAS modeling as a cross-modal alignment and conditional generation problem. We first propose XASLip, an alignment recipe coupling a physics-aware spectral encoder with an absorberaware manifold optimization strategy to resolve fine-grained intra-element coordination variations. Building upon this shared latent space, we formulate forward prediction as anchored absolute-spectrum generation via retrieval-augmented decoding, effectively preventing physical scale collapse and energy drift. For the inherently ill-posed inverse problem, we introduce Permutation-Rectified Flow Matching, which integrates type-wise optimal transport into a continuous generative flow to provide a principled solution to ligand permutation ambiguity without relying on heavy high-order equivariant architectures. Evaluated on a largescale standardized benchmark of 328,839 structure-spectrum pairs, Uni-XAS demonstrates strong performance in cross-modal retrieval, accurate absolute-spectrum prediction, and composition-conditional 3D structure generation, establishing a scalable, reproducible, and protocol-consistent foundation for multimodal learning and standardized evaluation in scientific spectroscopy.
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All authors Suyang Zhong, Yuhao Zhao, Boying Huang, Fanjie Xu, Pengwei Xu, Haoyi Tao, Xi Fang, Jun Cheng, Fujie Tang

Materials Science

Visualizing Microwave-Driven Dynamics of Antiskyrmions and Surface Skyrmions

Zhuolin Li, Daisuke Nakamura, Spencer Reisbick et al. (+9 more)

Microwaves provide coherent access to low-energy excitations and serve as effective probes of high-frequency spin dynamics in quantum and magnetic systems. For topological spin textures, microwave excitation is expected to generate rich collective responses, yet direct real-space observation of ultrafast dynamics remains limited. Here we use time-resolved Lorentz transmission electron microscopy to visualize microwave-driven dynamics in a hybrid antiskyrmion structure composed of a central antiskyrmion and surface skyrmions. We resolve the picosecond evolution of antiskyrmion area and second-harmonic signals, evidencing nonlinear responses of spin textures under microwave excitations. We track the core motions of the antiskyrmion and surface skyrmions, which follow distinct trajectories while sharing the same rotational sense. Micromagnetic simulations reproduce the key observations and associate the dynamic modes with the spatial modulation of the core profile along the thickness. These achievements establish ultrafast electron microscopy as a powerful real-space approach for probing high-frequency microwave-driven dynamics of topological magnetic solitons.
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All authors Zhuolin Li, Daisuke Nakamura, Spencer Reisbick, Chuhang Liu, Myung-Geun Han, Kosuke Karube, Wataru Koshibae, Naoto Nagaosa, Yasujiro Taguchi, Yimei Zhu, Yoshinori Tokura, Xiuzhen Yu

Materials Science

Orbital Hall Effect Enables Field-Free Magnetization Reversal in Ferrimagnets without Additional Conversion Layer

Zelalem Abebe Bekele, Kun Lei, Xiukai Lan et al. (+8 more)

The spin Hall effect provides a well-established route for electrical magnetization control, while the orbital Hall effect offers a powerful yet less explored source of angular momentum. Achieving field-free deterministic switching in straightforward orbital-torque architectures remains challenging. Here, we demonstrate orbital-Hall-current-driven switching in a Mo/CoGd bilayer without the need for a separate orbital-to-spin conversion layer across a wide temperature range. In this simplified geometry, Mo serves as both an orbital and spin current source. However, the spin contribution is insufficient due to weak spin-orbit coupling, which is consistent with first-principles calculations predicting a large orbital Hall conductivity. The adjacent ferrimagnetic CoGd layer provides both orbital-to-spin conversion and the perpendicular switching medium. Planar Hall and current-induced loop-shift measurements reveal a substantial unconventional z-polarized damping-like torque originating from interfacial symmetry breaking. Increasing the Mo thickness from 0.2 to 2 nm increases torque efficiency by approximately 31% (y-polarized) and 71% (z-polarized) components. This enhancement enables field-free deterministic switching with a critical current density down to 2.51 x 10^6 A cm^-2. Our results establish Mo/CoGd bilayers as a compact platform for orbital-current switching and point toward low-power orbitronic memory devices.
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All authors Zelalem Abebe Bekele, Kun Lei, Xiukai Lan, Xiangyu Liu, Hui Wen, Weihao Li, Yongcheng Deng, Wenkai Zhu, Kaiming Cai, Lishu Zhang, Kaiyou Wang

Materials Science

Long- and Short-Range Anion Order in SrTiO$_{3-x}$H$_x$ Perovskite Oxyhydrides: DFT+$U$ Sensitivity and HSE06 Cluster Expansion

Tzu-chen Liu and Chris Wolverton

Anion ordering in perovskite oxyhydrides can remain significant even in disordered states, particularly at non-dilute hydrogen concentrations. Nevertheless, hydride substitution poses challenges for accurate simulations based on density functional theory due to configurational complexity and Ti 3$d$ reduction. Here, we develop a cluster expansion (CE) framework for SrTiO$_{3-x}$H$_x$ incorporating HSE06 hybrid-DFT energetics. We first demonstrate that calculated mixing energies and ordering stability are highly sensitive to the choice of DFT+$U$, with maximum variations on the order of 100 meV/anion. We benchmark ordering energetics against HSE06 calculations and identify $U$ = 3.3 eV as an HSE06 proxy, which enables extensive configurational exploration while limiting costly HSE06 calculations to key configurations for efficient learning of ordering energetics. Together, ground-state orderings, correlations between octahedral configurations and structural stability, and MC sampling of CE models all support a strong preference for the O$_4$H$_2$ cis configuration in SrTiO$_{3-x}$H$_x$, in which two hydride ions occupy first-nearest-neighbor anion sites. This cis-type preference was overlooked in previous ATiO$_{3-x}$H$_x$ studies, despite its sizable stabilization of ~200 meV per hydride comparable to reported anion-migration and polaron-formation energies. This study addresses both the previously underexplored sensitivity of CE-based ordering analyses to DFT+$U$ and anion-ordering in perovskite oxyhydrides.
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Materials Science

MatDiffract: A Material-Informed Automated Analysis Platform for X-ray Powder Diffraction

Hongqing Wang, Mingwei Chen, Hongjie Luo et al. (+5 more)

High-throughput experimentation and self-driving laboratories are drastically accelerating materials discovery, yet automated interpretation of X-ray powder diffraction (XRPD) data remains a critical rate-limiting step. Conventional search-match workflows rely heavily on expert manual intervention, while pure data-driven machine learning approaches suffer from limited generalizability across chemical systems and lack rigorous crystallographic interpretability. Here we present MatDiffract, a material-informed automated analysis platform for high-throughput XRPD characterization. Built on a first-principles density functional theory (DFT)-derived inorganic crystal structure database, Atomly, MatDiffract constructs a perturbation-augmented simulated diffraction database, embeds multi-scale diffraction features into indexable vectors, and integrates hierarchical vector retrieval with full-pattern fitting Rietveld refinement and quantitative phase fitting. Benchmarked on 875 single-phase experimental patterns, the platform achieves 91.3% Top-1 and 97.2% Top-10 identification accuracy after automated refinement. For binary and ternary multiphase mixtures, it delivers 85.0% and 70.0% Top-1 accuracy with mass fraction mean absolute errors as low as 1.2% and 1.8%, respectively. Beyond mere phase labeling, MatDiffract outputs full crystallographic results including refined structural models, fitted profiles, and quantitative compositions within tens of seconds per sample. Its modular vector-based architecture supports seamless incremental expansion to new material systems, providing an end-to-end solution to close the characterization throughput gap for autonomous materials discovery and high-throughput materials development.
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All authors Hongqing Wang, Mingwei Chen, Hongjie Luo, Wen Yin, Fazhi Qi, Xuqing Chai, Miao Liu, Fengyao Hou

Materials Science

Photo-induced currents and short-term memory for reservoir computing in a ferroelectric semiconductor

Yan Meng Chong, Atreya Majumdar, Manuel Zahn et al. (+3 more)

Physical reservoir computing represents an energy efficient approach for processing temporal signals by exploiting the intrinsic nonlinear dynamics and fading memory of a physical system. Recently, ferroelectric semiconductors moved into focus as reservoir materials motivated by their versatile electronic responses to external stimuli. Here, we explore the fundamental possibility to recognize time-varying light pulses via photo-induced currents, using the small-band-gap p-type semiconductor ErMnO$_3$ as a model system. Under white light illumination, ErMnO$_3$ exhibits non-linearly evolving photo-induced currents and controllable relaxation dynamics that naturally realize the high-dimensional projection and fading memory capabilities required for reservoir computing. The reservoir capability of ErMnO$_3$ is reflected by the improved recognition accuracy of "Past" input pulses, which increases from ~33% to ~93% after applying reservoir transformation to the input signal. The results present ferroelectric hexagonal manganites as a promising platform for photo-induced current-based reservoir computing and highlight the potential of light-driven oxide semiconductors for temporal information processing.
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All authors Yan Meng Chong, Atreya Majumdar, Manuel Zahn, Ingvild Hansen, Karin Everschor-Sitte, Dennis Meier

Wednesday 22 July

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

Radiotracer photoluminescence for element-specific identification of color centers

Brecht Biesmans, Afonso Lamelas, Kirill Danilov et al. (+8 more)

We report on the implementation of a radiotracer photoluminescence spectroscopy setup at the ISOLDE radioactive ion beam facility at CERN, enabling element-specific identification of optically active defects in solids. The method combines radioactive ion implantation with optical spectroscopy, allowing the temporal evolution of photoluminescence signals to be correlated directly with nuclear decay. The setup is currently optimized for color centers in diamond and related wide-bandgap materials and enables room-temperature measurements. The system consists of an optical microscope coupled to a fiber-fed Czerny-Turner spectrometer with a liquid-nitrogen-cooled CCD detector, providing the stability required for long-duration measurements. As a proof-of-principle, radioactive $^{75}$Ga was implanted into diamond as a precursor to produce $^{75}$Ge impurities. The photoluminescence band extending from 600 nm, corresponding to the well-known GeV$^{-}$ center, exhibits an exponential decay with a half-life of $82.3^{+2.5}_{-2.3} \mathrm{min}$, in agreement with the known $\beta^{-}$ decay half-life of $^{75}$Ge of $82.78(4) \mathrm{min}$. This establishes a direct and unambiguous correlation between the observed spectral feature and its germanium origin. These results demonstrate the capability of the setup to perform element-specific optical spectroscopy and extend radiotracer methods to color centers in wide-bandgap materials, taking advantage of the uniquely broad range of radioactive isotopes available at ISOLDE.
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All authors Brecht Biesmans, Afonso Lamelas, Kirill Danilov, Aleksandr Seliverstov, Ângelo Costa, Vítor Amaral, André Vantomme, João Guilherme Correia, Ulrich Wahl, Lino M. C. Pereira, the ISOLDE Collaboration

Materials Science · Cross-listed from cond-mat.stat-mech

Statistical Mechanics of Thermal Diffusion in Rough Energy Landscapes

Soham Chattopadhyay and Blas P. Uberuaga

Starting from a variational principle for mass transport, we present a broadly applicable statistical framework describing thermal diffusion in complex solids. We show that microscopic thermodynamic and kinetic fluctuations govern non-Arrhenius diffusion, with kinetic terms described by machine-learnable relative diffusion contributions. For vacancy diffusion in solid solutions, deviation from Arrheniusness may occur when ordering effects start to become important but at higher temperatures, approximately Arrhenius behavior can occur, aided by configurational entropy and competing energy fluctuations.
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Materials Science

Generative and multimodal AI for materials prediction and design: Progress, challenges, and perspectives

Xianyuan Liu, Charles Anjah, Benjamin E. Jolly et al. (+9 more)

Artificial intelligence (AI) is accelerating materials prediction and design by enabling efficient exploration of chemical and structural spaces, with particular promise for novel materials discovery. However, novelty in materials discovery encompasses chemical plausibility, structural distinctiveness, property relevance and experimental realisability, making AI-driven novelty claims difficult to substantiate. We introduce a materials property hierarchy, from intrinsic, composition-determined properties to extrinsic, processing-dependent performance, to clarify deployment constraints and distinguish structural, physical and deployment novelty. This framework motivates an evidence-based view of multimodal materials data spanning chemical composition, microstructure, processing, and testing and characterisation, showing that current evidence remains concentrated in composition and idealised structure while heterogeneous, under-represented and weakly integrated modalities limit support for physical and deployment novelty. It also highlights the limitations of benchmarks based mainly on computational labels and proxy novelty criteria. Community-wide standards for data collection, modality alignment and evidence synthesis are needed to support multimodal data construction, process-aware multimodal modelling, feasibility-first generative modelling and deployment-aware benchmarking, so that generative and multimodal AI can design experimentally realisable materials with defensible scientific and practical novelty.
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All authors Xianyuan Liu, Charles Anjah, Benjamin E. Jolly, Jonathon F. S. Markanday, Joshua Berry, Haolin Wang, Nicola A. Morley, Robert D. J. Oliver, Alexandra J. Ramadan, Delvin Ce Zhang, Katerina A. Christofidou, Haiping Lu

Materials Science

First-principles calculation of electron-phonon spectral functions for defects using phonon interpolation

Zoltan Santha and Gergo Thiering

Point defects in wide-band-gap semiconductors exhibit optical spectra strongly shaped by electron-phonon coupling, but direct first-principles calculation of the corresponding phonon sidebands is often limited by the coarse vibrational spectrum of the largest defect supercells accessible by ab-initio electronic structure codes. In this work, we present a phonon-interpolation method for Huang-Rhys spectral densities and optical lineshape functions on hypercells created by extending the defect-containing supercells on arbitrarily dense phonon $q$-point grids. The method is based on reconstructing the transition-induced force associated with the optical excitation and using this localized force source to couple the defect transition to a densely sampled vibrational continuum. In this formulation, the local defect physics is obtained from ab initio supercell calculations, while the long-wavelength acoustic modes and the detailed structure of the host phonon spectrum are recovered by diagonalizing interpolated dynamical matrices in large hypercells. We demonstrate the method on the negatively charged nitrogen-vacancy centre in diamond between its ground $^{3}A_{2}$ and excited $^{3}E$ states. The transition-force is shown to be strongly localized around the defect, with converged localization measures obtained in a $4\times4\times4$ supercell accessible by density functional theory calculations. We interpolate the electron-phonon coupling on hypercells up to $32\times32\times32$ corresponding to approximately 17 million atoms, thereby recovering smooth, continuous Huang-Rhys spectral densities with ultrafine spectral resolution. The dominant coupling band is found near 63~meV; the low-energy acoustic contribution follows the expected linear scaling; and we recover the finer van-Hove-related structures in the optical phonon regime observed in experiments.
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Materials Science

Analytical Forces from the Bethe-Salpeter Equation for Large-Scale Excited-State Relaxation

Yu Jin, Victor Wen-zhe Yu, Marco Govoni et al. (+1 more)

We present an efficient plane-wave implementation of analytical nuclear forces for electronic excited states described by the Bethe-Salpeter equation (BSE). The formulation combines density-matrix perturbation theory with a Lagrangian approach, and avoids both explicit empty-state summations and the response calculations for each atomic displacement, required by conventional approaches based on density functional perturbation theory. Together with GPU acceleration, these advances make BSE forces calculations tractable for solid-state systems containing hundreds of atoms. We demonstrate the method on two point defects with distinct dielectric environments: the nitrogen-vacancy center in diamond, where BSE and time-dependent density functional theory (TDDFT) yield consistent excited-state relaxations, and the carbon-dimer defect in two-dimensional hexagonal boron nitride, where the screened electron-hole interaction included in the BSE stabilizes the localized defect excitation and corrects the relaxation pattern predicted by semilocal TDDFT. These results establish a scalable framework for BSE-level studies of excited-state relaxation and vibronic coupling in heterogeneous condensed systems.
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All authors Yu Jin, Victor Wen-zhe Yu, Marco Govoni, Giulia Galli

Materials Science

A high-dimensional neural network potential for finite-temperature phenomena in NiTi martensite

Petr Jaroš, Petr Sedlák, Petr Šesták et al. (+3 more)

We present a high-dimensional neural network potential (HDNNP) for the martensitic phase of the NiTi shape-memory alloy trained to density functional theory (DFT) data. A central aspect of this work is the systematic validation of the potential with respect to the underlying DFT reference method for key properties governing structural evolution, including equilibrium crystal structures, elastic constants, generalized-stacking fault energies, and vibrational spectra. The HDNNP accurately describes the relative stability of the B19$^\prime$ and B33 phases, including subtle energy differences on the order of meV/atom. The predicted stacking-fault energy landscape is strongly anisotropic and reveals a preferential shear pathway, providing atomistic insight into deformation and twinning mechanisms. Finite-temperature molecular dynamics simulations further enable the investigation of unconstrained structural evolution as a function of temperature. Overall, the developed HDNNP provides a robust basis for atomistic simulations of the complex structural and functional behavior of martensitic NiTi systems containing hundreds of thousands of atoms on nanosecond time scales.
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All authors Petr Jaroš, Petr Sedlák, Petr Šesták, Miroslav Černý, Jörg Behler, Hanuš Seiner

Materials Science · Cross-listed from cs.RO

Scalable Low-Cost Laboratory Automation: A Digital Twin-Integrated Robotic Platform for Autonomous Liquid Handling (RAINBOT)

Mohamed Rami Ayeche, Souhil Sid, Ahyen Mostofa et al. (+3 more)

Laboratory automation accelerates discovery, yet its adoption is constrained by the high cost, proprietary design, and limited remote supervisability of commercial liquid-handling systems. This work presents RAINBOT\textsuperscript{TM}, a low-cost, openly reproducible liquid-handling robot built by converting a consumer-grade Cartesian 3D printer (Elegoo Neptune 4 Max). The printer extruder is replaced by a precision single-channel pipette actuated through the printer's own G-code-driven X–Y–Z gantry, with plunger and tip-eject motions effected by two compact linear actuators under Python control. To make experiments transparent and remotely supervisable, a browser-based digital twin is implemented to synchronise bidirectionally with the physical platform, mirroring kinematics and pipetting states in real time and exposing remote monitoring, intervention, and an emergency stop from any web browser. As a proof of concept, RAINBOT\textsuperscript{TM} performed sequential exchanges of differently coloured aqueous solutions while an integrated colour sensor quantified the resulting mixtures; measured red, yellow, and blue (RYB) responses agreed with expected mixing behaviour to within a mean absolute error of two percentage points, validating correct execution and real-time tracking. Closing the loop, the platform is coupled to the CEID\textsuperscript{TM} (Cooperative Explorer for Inverse Design) framework, which recasts experimentation from iterative manual guessing into a goal-directed inverse-design search while keeping a human in the loop. The complete hardware costs under US\$1300, which is roughly an order of magnitude below entry-level commercial handlers, thereby establishing an accessible physical–virtual framework for self-driving laboratory automation.
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All authors Mohamed Rami Ayeche, Souhil Sid, Ahyen Mostofa, Rehaan Hussain, Ali Shayesteh, Fadwa El Mellouhi

Materials Science

Magnetic ground states of CrPS$_4$ and NiPS$_3$ monolayers from long-range exchange interactions

Balazs Nagyfalusi, Ritesh Das, Alvaro Bermejillo-Seco et al. (+4 more)

We investigate the magnetic properties of monolayer CrPS$_4$ and NiPS$_3$ by combining first-principles calculations, second-principles spin models, and Monte Carlo simulations. Unlike conventional approaches that truncate exchange interactions after only a few shells and determine them by fitting total energies, we extract the magnetic exchange tensors directly from density functional theory using the LKAG formalism and include interactions until numerical convergence is achieved. We show that long-range exchange interactions qualitatively modify the magnetic behavior of both materials. In CrPS$_4$, they destabilize the previously predicted ferromagnetic ground state and stabilize a spin-spiral phase, reducing the critical temperature to about 21\,K, in agreement with available experiments. The resulting magnetic phase diagram contains multiple collinear and non-collinear phases that can be tuned by temperature and external magnetic fields. In NiPS$_3$, the experimentally observed zigzag antiferromagnetic order only emerges when exchange interactions up to the fifth shell are included. These results demonstrate that quantitatively predictive spin models for thiophosphate monolayers require long-range exchange interactions and provide a predictive framework for accurately describing two-dimensional van der Waals magnets.
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All authors Balazs Nagyfalusi, Ritesh Das, Alvaro Bermejillo-Seco, Herr S. J. van der Zant, Yaroslav M. Blanter, Amador Garcia-Fuente, Jaime Ferrer

Materials Science · Cross-listed from cond-mat.mes-hall

Ideal Bands in Tight-Binding Models

Lexu Zhao, Yang Ge, Shinsei Ryu et al. (+1 more)

A band is called ideal when its Dirichlet functional saturates the topological lower bound. We study ideal bands in finite-band tight-binding models with conventional two-dimensional lattice translation symmetries, allowing the bands to have non-flat dispersion. We first provide an analytic construction of isolated Chern-ideal bands with Chern number $|\mathrm{Ch}|=1$ in finite-band models with exponentially decaying hopping. This construction applies only when at least two orbitals have different embedded positions (modulo lattice vectors), complementing the previously known construction for $|\mathrm{Ch}|>1$. We then show that isolated Chern-ideal bands with any nonzero Chern number cannot exist in finite-band models with finite-range hopping, regardless of the embedded orbital positions. The conclusion holds even if there are isolated band touching points, as long as the Berry curvature does not diverge anywhere in the Brillouin zone. We finally generalize the conclusions to Wilson-loop-ideal bands with zero total Chern number, such as Kane-Mele $\mathbb{Z}_2$-ideal bands.
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All authors Lexu Zhao, Yang Ge, Shinsei Ryu, Jiabin Yu

Materials Science

Lithium-Projected Phonon Spectral Distributions as Robust Descriptors of Ionic Conductivity in Solid Electrolytes

Gajendra Bohara and Ramakrishna Podila

Lattice dynamics are widely invoked in the design of solid electrolytes, yet phonon information is commonly compressed into a band center or another scalar softness measure. Here we test whether the complete lithium-projected phonon density of states (Li-PDOS) provides a reproducible descriptor of experimental room-temperature ionic conductivity. MatterSim forces and Phonopy were used to generate harmonic total and Li-projected spectra for crystallographically resolved entries in the OBELiX dataset. A composition and structure audit defined a primary cohort of 260 materials (212 train and 48 test), a strict cohort of 241, and an exact-composition cohort of 168. Across 20 independently generated phonon-calculation database comparisons, the mean Wasserstein-1 distance was 0.542 THz for total DOS and 0.731 THz for Li-PDOS, revealing broad agreement but systematic, projection-dependent softening. Higher conductivity was associated with redistribution of normalized Li spectral weight toward low frequencies: in the untouched test set, the Li fractions below 2 and 5 THz had Spearman coefficients of 0.333 and 0.374, while the 5$\%$ cumulative-frequency quantile had a coefficient of $-0.393$. A Wasserstein kernel on the full Li-PDOS achieved held-out $R^2=0.444$, compared with 0.012 for total DOS and 0.181 for a static composition–structure kernel. The Li model remained stable in the strict ($R^2=0.462$) and exact ($R^2=0.451$) cohorts. Family adjustment attenuated scalar associations, and Li-versus-total whole-spectrum dependence was cohort sensitive. The results therefore support mobile-ion-resolved spectral distributions as useful comparative screening descriptors, not as a universal causal softness law.
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Materials Science · Cross-listed from physics.optics

Probing the temperature dependence of dielectric function of ternary transition metal dichalcogenides: towards thermo-driven ultrathin photonic components

Artsruni Margaryan, Maria Levonyan, Maksim Sargsyan et al. (+4 more)

Transition metal dichalcogenides (TMDs), along with their ternary derivatives, have attracted considerable attention mostly due to pronounced excitonic resonances emerging in visible (Vis) and near-infrared (NIR) spectral regions, enabling strong light-matter interaction. Nevertheless, a comprehensive insight of the temperature-dependent optical dispersions for the most of representatives of the family remains yet unrevealed. Here, we report on systematic studies of dielectric permittivity functions of uniaxial ternary MoSSe and WSSe across 430-1000 nm spectral region over a broad temperature window of 80-670 K. We show that the temperature evolution of their dielectric responses is governed by Varshni's formalism in Vis spectral region further affecting their high refractive index properties at the lossless NIR spectral tails. Furthermore, we exploit the measured optical dispersion of ternary WSSe designing ultrathin plano-convex NIR photonic lenses that demonstrate continuous modulation of performance with temperature variation. Our work provides critical insights for the creation of next-generation thermo-driven nanophotonic and optoelectronic devices.
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All authors Artsruni Margaryan, Maria Levonyan, Maksim Sargsyan, David Karakhanyan, Meri Hayrapetyan, Kostya S. Novoselov, Davit A. Ghazaryan

Materials Science

Competing ferromagnetic and antiferromagnetic interactions in non-altermagnetic Ru$_{1-x}$Cr$_{x}$O$_{2}$

David T. Plouff, Nawsher J. Parvez, Subhash Bhatt et al. (+4 more)

We investigate the proposal of hole doping RuO$_{2}$ via alloying with Cr ions to induce altermagnetism. Thin film samples of Ru$_{1-x}$Cr$_{x}$O$_{2}$ ($0 \leq x \leq 0.28$) were prepared by reactive magnetron co-sputtering on TiO$_{2}$ substrates, with epitaxial nature verified by X-ray diffraction and composition depth profiles determined by X-ray photoelectron spectroscopy combined with Ar etching. Neutron diffraction measurements of samples with $x = 0$ and $x = 0.23$ at low temperatures show no evidence of long-range altermagnetic order with spins oriented along the $c$-axis or within the $ab$-plane. In contrast, temperature dependent susceptibility measurements in samples with $x \geq 0.16$ show a gradual downturn below $T\approx20~$K, suggestive of antiferromagnetic interactions, although this coexists with ferromagnetic hysteresis and remnant magnetization at $4~$K for samples with $x \geq 0.23$. Together, our magnetometry and neutron scattering measurements suggest the coexistence of antiferromagnetically coupled ferromagnetic CrO\textsubscript{2} clusters. This indicates that Cr ions do not hole dope Ru bands to induce an altermagnet state, but rather the holes remain localized to the Cr ions.
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All authors David T. Plouff, Nawsher J. Parvez, Subhash Bhatt, Xixiang Zhang, Adam A. Aczel, Jonathan Gaudet, John Q. Xiao

Materials Science · Cross-listed from cond-mat.str-el

Magnetoresistive Memory in the Paramagnetic Phase of Eu$_5$In$_2$As$_6$

Sudhaman R. Balguri, Mira B. Mahendru, Rourav Basak et al. (+9 more)

Magnetoresistive materials that respond sensitively to applied fields are central to modern data storage technologies. Here we unveil a novel Magnetoresistive Memory (MRM) in Eu$_5$In$_2$As$_6$, where the electrical resistivity depends not only on the magnitude but also on the history of the applied magnetic field. Such an effect has been reported in only two classes of strongly correlated electron systems: perovskite manganites and pyrochlore iridates. In both cases, the effect has been observed in the magnetically ordered phase. It has been attributed to metastable magnetic states in manganites and conducting domain walls in iridates. Remarkably, the MRM in Eu$_5$In$_2$As$_6$ onsets at twice the antiferromagnetic transition temperature, well within the paramagnetic phase. The temperature, field, and time dependence of resistivity suggest that either a hidden order or a fluctuating phase with short-range correlations underlies this effect. Our results offer MRM as a new platform for quantum sensing and memory technologies, and encourage searching for MRM in related materials.
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All authors Sudhaman R. Balguri, Mira B. Mahendru, Rourav Basak, Enrique O. González-Delgado, Adam A. Aczel, David E. Graf, Andreas Rydh, Christopher C. Homes, Jonathan Gaudet, Ying Ran, Alex Frano, Fazel Tafti

Materials Science

Role of Resonant $\mathbf{k}$-Points in the Transient Optical Response of Pumped Germanium

Amir Eskandari-asl, Giacomo Inzani, Matteo Lucchini et al. (+1 more)

Pump-induced transient optical properties combine contributions from electronic states throughout the Brillouin zone, but the relative relevance of off-resonant and l-photon resonant crystal momenta has remained unexplored. We address this issue in pumped germanium by resolving the transient absorptive response into momentum-space classes defined by the presence or absence of 1-, 2-, and 3-photon resonances with respect to the pump. Using the Dynamical Projective Operatorial Approach together with the related generalized linear response theory, we compute the differential imaginary part of the dielectric function and evaluate the contributions of each resonance class. Resonant regions account for nearly the entire optical response, whereas points outside the identified resonance sets contribute only negligibly. Nevertheless, the 2-photon-resonant set, although containing more than 98% of the residual (post-pump) excitation population, does not reproduce the full transient spectrum. Conversely, resonance classes with very small residual populations generate non-negligible contributions to the transient optical properties. This mismatch shows that the transient optical weight is not determined solely by the real-charge dynamics (which results in post-pulse residual excitation population) and is consistent with substantial virtual pump-induced contributions, whose dominant optical weight nevertheless arises from the resonant regions of momentum space. The class-resolved phase of the dominant 2$\omega_{\mathrm{pu}}$ oscillations further shows that, whenever a class contributes appreciably, the phase of its oscillatory component follows that of the corresponding full signal. The resulting decomposition provides a momentum-resolved connection among multi-photon resonances and transient optical observables in a realistic material.
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All authors Amir Eskandari-asl, Giacomo Inzani, Matteo Lucchini, Adolfo Avella

Materials Science · Cross-listed from quant-ph

Coupling phase interference effects in a multimode cavity magnonics system

M. Avicena, G. Bourcin, V. Vlaminck et al. (+2 more)

Coupling phases play a decisive yet often overlooked role in cavity magnonics, particularly in complex multimode systems. Here, we investigate phase-mediated interference effects in a cavity magnonics system comprising a four-post re-entrant microwave cavity coupled to Yttrium Iron Garnet (YIG) spheres. Using an input-output model that explicitly accounts for both internal and external coupling phases, we achieve agreement with experimental microwave transmission measurements. Our results unravel the emergence of a positionally-dependent uncoupled mode due to interference of cavity photon-magnon (internal) coupling phases. Further, we experimentally observed large nonreciprocity at the antiresonance frequencies and show that this feature arises due to the far-detuned modes' odd parity cavity photon-probe (external) coupling phase interfering with the internal coupling phases. Bridging theory, simulation and experiment, these results establish coupling-phase engineering as a key principle for accurately modeling and designing multimode cavity magnonics devices.
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All authors M. Avicena, G. Bourcin, V. Vlaminck, J. Bourhill, V. Castel

Materials Science · Cross-listed from cond-mat.soft

A Theoretical Framework for the Coupling of Macroscale-Nanoscale Mechanochemical Phenomena in Condensed Matter

Brenden W Hamilton

The field of covalent mechanochemistry has transitioned from fundamental science to engineering applications, yet it lacks a robust theoretical framework for predicting reaction kinetics in condensed matter. Existing analytical models fail under realistic conditions where macroscopic strains drive molecular-scale deformations that are highly non-linear. We develop a non-perturbative theoretical framework that captures activation barrier changes in highly strained molecules undergoing complex, non-linear deformations, describing the macroscale-nanoscale coupling of phenomena. The framework yields general expressions, parameterizable from atomistic simulations, enabling multiscale prediction of mechanochemical behavior. By presenting the expressions in terms of general observables, this work enables predictions of mechanochemical effects from simple structure optimization calculations, enabling the use of high level quantum chemical methods. We demonstrate this approach on the mechanochromic polymer spiropyran, showing how non-linear strain fields govern mechanophore activation.
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Materials Science

From MLIPs to Microstructure: A High-Throughput Computational Framework to Design Spinodal Alloys in High-Dimensional Composition Spaces via Analytic Derivatives of CALPHAD Model Predictions

Courtney Kunselman, Doguhan Sariturk, Siya Zhu et al. (+2 more)

Identifying regions of design space subject to spinodal decomposition is a critical component of alloy design in high-dimensional composition spaces. In cases where designers are seeking to exploit spinodal microstructures to tailor alloy properties, prediction of microstructure evolution and morphology is also needed. In this work, we present a Machine Learning Interatomic Potential (MLIP)-trained, CALPHAD-based, open-source workflow for high-throughput microstructure stability analysis and visualization. In this workflow, coherent strain contributions are captured via high-throughput MLIP elastic constant calculations. To predict microstructure morphology for compositions of interest, MLIP-generated thermodynamic models are fed into an elasto-chemical phase field simulation. Both stability analyses and phase-field simulations utilize analytically-derived Gibbs energy Hessians to improve computational efficiency and accuracy over finite difference approximations. We demonstrate this workflow by investigating microstructure stability in the Hf-Nb-Ti-V quaternary system.
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All authors Courtney Kunselman, Doguhan Sariturk, Siya Zhu, Vahid Attari, Raymundo Arroyave

Materials Science

Kinetically-Arrested Phase Separation leads to Tunable Domain Structures in Vapor-Deposited Glasses

A T M Mahbub Alahe, Thomas J. Ferron and Camille E. Bishop

The characteristic length scale of phase-separated organic thin film blends is a critical structural parameter governing the performance and functionality of organic electronic devices. The arrested morphologies of vapor-deposited organic thin films result from the interplay between thermodynamic driving forces and kinetic constraints during deposition. Here, we aim to isolate the role of kinetic effects in phase separation by varying the deposition rate at a constant substrate temperature for a co-deposited molecular glass blend of N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) and Disperse Orange 37 (DO37). The dependence of morphology on deposition rate is quantified using power spectral density (PSD) analysis of atomic force microscopy (AFM) images. Two distinct deposition rate-dependent length scales at the surface reveal how deposition kinetics directly influence domain size and film topography. Complementary Resonant Soft X-ray Scattering (RSoXS) measurements indicate that phase separation extends throughout the film thickness. These observations are consistent with the surface equilibration mechanism previously described for homogeneous vapor-deposited films, in which enhanced surface mobility allows molecules in the growing film to partially equilibrate into distinct surface-templated states during deposition. In the current work, this mechanism allows the multi-component blend to phase separate and coarsen into a structure with multiple length scales before kinetically arresting to an extent that depends on the deposition rate. The demonstration of finely tunable domain size with deposition rate provides strategies to design new organic electronic devices with desired morphologies.
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Materials Science · Cross-listed from cs.AI

Reading and Steering Representations of Materials-Science Mechanisms in an Open-Weight Language Model

Markus J. Buehler

Large language models can answer scientific questions, yet a correct output does not reveal whether the model represents or uses the governing physics. Here, using three open-weight Gemma 4 models (google/gemma-4-E4B-it, google/gemma-4-12B-it, google/gemma-4-31B-it) we identify three experimentally separable signatures of materials-science mechanism information: selective concept readability, relational encoding of qualitative constitutive orientation, and causal, context-dependent control of constrained engineering answers. We combine matched direct and Jacobian vocabulary readouts, option-free state geometry, a 60-law counterfactual benchmark and causal interventions. In 50 held-out materials descriptions, three independently fitted Jacobian lenses reproduced concept ranks, and target-free word sets from both readouts enabled blinded identification of 9 of 10 mechanism families. A separate 72-prompt benchmark produced mechanism-specific hidden-state neighborhoods, but an exact graph audit showed that this apparent physical organization was equally explained by numerical comparison. We therefore compared otherwise identical prompts in which only the direction of the physical input was reversed, asking whether the resulting hidden-state movement followed the supplied constitutive law. These state transformations ordered direct, physically neutral and inverse laws across 60 frozen relations and correctly oriented 39 of 40 directional laws, whereas lexical controls were near chance. Bidirectional interventions shifted answer probabilities toward or away from the physically appropriate outcome across all 12 matched cases, while counterfactual state patches transferred opposing decision signals across mechanisms and answer formats. Physical relationships were therefore more visible in controlled state changes than in absolute states alone.
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