Materials Science · Cross-listed from physics.ins-det
Retrofitting a commercial RF induction generator into a computer-controlled, vacuum and gas integrated annealing system for reactive-metal grain growth
Sterling G. Baird, Ryan Weber, Christopher Nyborg et al. (+3 more)
High-temperature
vacuum annealing near a metal's melting point drives controlled grain growth, but it normally requires an expensive turn-key
vacuum induction furnace. We retrofit a bare commercial
radio frequency (RF) induction generator with computer power control through LabVIEW, dual-wavelength optical temperature feedback, and a high-
vacuum quartz-tube chamber with inert-gas backfill. A machined graphite crucible doubles as a susceptor, an RF-absorbing element that heats the specimen it encloses. The only requirement is a monotonic analog power-control input, so the retrofit transfers between generators. Our reference build uses a 6 kW solid-state generator. Surprisingly, nickel annealed in this system produced high-quality electron backscatter diffraction (EBSD) patterns with zero specimen preparation. Samples went directly from the furnace to the electron microscope without grinding, polishing, or etching. The EBSD maps indexed hundreds of equiaxed grains delineated by deep thermal grooves. A modified sample assembly extends the furnace to ceramics that do not couple to the RF field. It coarsened yttria-stabilized zirconia (YSZ) grains in 45 min at 2500{\deg}, compared with 228h at 1600{\deg} in a conventional box furnace. For a fixed configuration, the power-temperature calibration is linear ($R^2$ = 0.991) from 1200 to 1400{\deg}. Eight 12h nickel anneals at 1200{\deg} reproduced their soak temperature to 1201.2 $\pm$ 1.3{\deg}, and 40h soaks at 1325{\deg} remained stable. Complete design files, a bill of materials, control software, and data are openly available. This gives laboratories an affordable route to near-melting-point annealing with direct anneal-to-EBSD characterization.
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All authors Sterling G. Baird, Ryan Weber, Christopher Nyborg, Ronald Guymon, Gage Erickson, Oliver K. Johnson
Materials Science
Enhancement-Mode Vertical $\beta$-Ga$_2$O$_3$ U-Trench MOSFET with MOCVD Regrown n$^+$ Contact Layers and Nitrogen-Implanted Current Blocking Layer
Walid Amir, Jiawei Liu, Surajit Chakraborty et al. (+4 more)
In this work, an implantation-free ohmic contact technology based on selectively MOCVD-regrown Si-doped n$^+$ layers is demonstrated for enhancement-mode vertical $\beta$-Ga$_2$O$_3$ U-trench MOSFETs. The regrown n$^+$ contact structure eliminates the need for implantation-based ohmic contact formation while maintaining excellent electrical characteristics. A multi-energy nitrogen-ion-implanted current blocking layer (CBL) followed by 1100~$^\circ$C activation annealing in N$_2$ ambient for 30 min was employed to achieve normally-OFF operation. Transmission line model measurements yielded a low specific contact resistivity of $2.65 \times 10^{-7}~\Omega\cdot$cm$^2$. The fabricated devices exhibited a threshold voltage of approximately 5~V, an ON/OFF current ratio of $1.15\times10^{6}$, a peak current density of 158A/cm$^2$, and a specific ON-resistance of 120.9~m$\Omega\cdot$cm$^2$. Three-terminal OFF-state breakdown voltages ranging from 920 to 980~V were achieved at $V_{GS}=0$~V. Multi-finger MOSFETs show current scaling to 0.25 A. These results demonstrate that selectively MOCVD-regrown n$^+$ contact layers provide a promising implantation-free approach for realizing high-performance vertical $\beta$-Ga$_2$O$_3$ power MOSFETs.
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All authors Walid Amir, Jiawei Liu, Surajit Chakraborty, Dong su Yu, Md. Mosarof Hossain Sarkar, Hongping Zhao, Uttam Singisetti
Materials Science · Cross-listed from cond-mat.str-el
Tunable inter-bilayer magnetic correlations and candidate multipolar physics in the van der Waals oxyhalides DyOCl, DyOBr, and DyOI
F. C. Brooks, X. Bai, J. Bacsa et al. (+5 more)
Rare-earth van der Waals magnets provide a route to combining strong
spin-orbit coupling, large
magnetic moments, and reduced dimensionality in bulk
crystals. We report a comparative study of the dysprosium oxyhalides DyOX (X = Cl, Br, I), which realize square-bilayer networks of Dy3+ moments separated by a tunable van der Waals gap. Structural refinements show that increasing the halide ionic radius strongly expands the inter-bilayer spacing while leaving the local bilayer geometry nearly unchanged. Magnetization and heat-capacity measurements reveal two low-temperature anomalies in all three compounds: antiferromagnetic order at TN ~ 7-10 K and a broader anomaly near TQ ~ 27-30 K. Single-
crystal magnetization on DyOCl and DyOBr establishes a strong hard-c-axis anisotropy, consistent with
crystal-field analysis of DyOCl, which yields an XY-like ground-state g tensor.
Neutron diffraction shows long-range antiferromagnetic order in DyOCl, whereas DyOBr and DyOI exhibit sharp
magnetic scattering coexisting with Warren-like diffuse features, consistent with robust in-plane correlations and imperfect inter-bilayer registry. Inelastic
neutron scattering on DyOCl identifies
crystal-field excitations near 25-30 meV and an additional
magnetic mode near 10 meV whose temperature dependence is tied to the high-temperature anomaly. Taken together, these results establish DyOX as a tunable family of quasi-two-dimensional rare-earth magnets and point to candidate multipolar physics associated with low-lying
crystal-field states. Direct probes of quadrupolar order, such as resonant x-ray scattering or elastic-constant measurements, will be required to determine the order parameter at TQ.
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All authors F. C. Brooks, X. Bai, J. Bacsa, V. O. Garlea, S. Calder, N. Butch, M. B. Stone, M. Mourigal
Materials Science
Dynamic Ensembles of Phosphine-Stabilized Gold Nanoclusters
Caitlin A. McCandler, Disha Sanwal and Jutta Rogal
Atomically precise phosphine-stabilized gold nanoclusters are commonly characterized by single-
crystal X-ray diffraction, yet the extent to which these static structures represent finite-temperature behavior remains unclear. To explore the free-energy landscapes,
equilibrium populations, and isomerization kinetics of these nanoclusters in the gas phase, we establish a general framework that combines molecular dynamics simulations based on a machine-learned interatomic potential with Markov state models (MSMs). Analysis of the MSMs indicates that experimentally reported
crystal structures frequently correspond to minor metastable states or transient configurations rather than the dominant finite-temperature structures. Increasing ligand coverage systematically alters both the thermodynamics and kinetics of structural rearrangements, driving the transition from planar to three-dimensional gold cores while accelerating isomerization dynamics. Moreover, catalytically accessible geometries are often only minor members of the
equilibrium ensemble, highlighting a trade-off between structural stability and surface accessibility. These results emphasize that ligand-protected nanoclusters need to be viewed as dynamic ensembles and their finite-temperature behavior cannot be fully captured by their corresponding crystallographic structures alone.
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Materials Science · Cross-listed from cond-mat.soft
Layered matter that maintains spacing but loses stacking order
Osvaldo Trigueiro Neto, Paulo Henrique Michels-Brito, Bruno Ceccato Telli et al. (+5 more)
In layered materials, spacing and stacking-order extent are usually locked. Here we show that in swollen suspensions of stiff, charged nanosheets they decouple, and that this defines a distinct regime, apart from the crystalline- and Wigner-swelling regimes such systems usually occupy. The mean spacing stays sharp and salinity-tunable while scattering-weighted stacking spans only two to three layers. We demonstrate this in a near-perfect model material, so the behaviour is intrinsic, not defect-driven. X-ray and
neutron scattering, sedimentation and a Donnan analysis show the spacing is held by a parameter-free osmotic restoring slope below one pascal per nanometre. Because the slope is so weak, the spacing sits at
equilibrium while faults relax slowly, a quenched metastable registry whose ageing-like relaxation of low-dimensional periodic order has not, to our knowledge, been realised before. The same decoupling is expected across stiff, swollen nanosheets, from clays to oxide nanosheets and
graphene oxide.
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All authors Osvaldo Trigueiro Neto, Paulo Henrique Michels-Brito, Bruno Ceccato Telli, Natalie Jasmin Eichstaedt, Leide P. Cavalcanti, Tomás S. Plivelic, Josef Breu, Jon Otto Fossum
Materials Science
Cumulative X-ray Damage in Bismuth Selenide Examined by Simultaneous TXM and XRD
Sophie E Parsons, Bernard Kozioziemski, Daewoong Nam et al. (+21 more)
Bismuth selenide (Bi2Se3) is a topological
insulator with potential applications in thermoelectrics, spintronics, and optoelectronics. However, its response to radiation remains poorly understood. We investigate cumulative X-ray damage in Bi2Se3 using simultane- ous transmission X-ray microscopy (TXM) and X-ray diffraction (XRD) at the Pohang Accelerator Laboratory X-Ray Free Electron
Laser (PAL-XFEL) over 27,000 successive pulses. We observe distinct damage mechanisms: rapid hole formation via vaporization within 100 pulses, followed by slower grain refinement and material sputtering over thousands of thermal cycles. Williamson-Hall analysis reveals a progressive transformation from single-
crystal to nanocrystalline structure, with grain sizes decreasing from mi- cron to nanometer scale. Finite-element modeling confirms that X-rays penetrate 13.47 {\mu}m, driving local temperatures above 1600 K with subsequent cooling between pulses. Scanning electron microscopy identifies three characteristic morphologies correspond- ing to different thermal histories: sputter streaks, prismatic
crystals, and disordered microcrystals. Our results demonstrate that grain-boundary formation creates a feedback mechanism that accelerates damage in later pulses. This work establishes a method- ology for studying radiation damage across multiple length scales and provides insight into topological
insulator stability under extreme conditions
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All authors Sophie E Parsons, Bernard Kozioziemski, Daewoong Nam, Eric Folsom, Can Yildirim, Sean Breckling, Sungwook Choi, Eric C. Galtier, Arnulfo Gonzalez, Deja Dominguez, Emlyn Frederick, Marylesa M. Howard, Sara Jessica Irvine, Kento Katagiri, Sangsoo Kim, Seonghan Kim, Sunam Kim, Stephan Kuschel, R. Stewart McWilliams, Norimasa Ozaki, Alison M. Saunders, Hyunjung Kim, Jon Eggert, Leora Dresselhaus-Marais
Materials Science
Multi-Tool Robotics Enables In-Situ Sample Manipulation for Time-Resolved Synchrotron Measurements
Aditya Bondada, Elizabeth M. Wall, Eric Yuan Xiao et al. (+4 more)
The high
photon flux at synchrotron beamlines allows for the measurement of fast dynamical processes. However, beamline radiation-safety protocols prohibit human intervention during X-ray experiments, limiting the ability to perform versatile real-time sample manipulations during continuous data acquisition. Here we present a robotic platform at an X-ray scattering beamline to enable real-time sample handling and processing in the experimental hutch, revealing previously inaccessible transient in-situ dynamics in perovskite thin films. This modular multi-tool robotic architecture enables in-hutch sample manipulation beyond human-access constraints, establishing a foundation for automated and autonomous synchrotron experimentation.
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All authors Aditya Bondada, Elizabeth M. Wall, Eric Yuan Xiao, Quinn C. Burlingame, Yueh-Lin Loo, Esther H. R. Tsai, Ruipeng Li
Materials Science
Avalanche-like Plasticity in Complex Concentrated Alloys: A Review Across Scales
Michal Knapek, Tomáš Tayari, Kristián Máthis et al. (+1 more)
Complex concentrated
alloys (CCAs), including high- and medium-
entropy alloys, deform in chemically heterogeneous energy landscapes where dislocation glide, solute aging, twinning, phase transformation and microstructural barriers may all contribute. This review discusses avalanche-like and serrated plasticity in CCAs across scales. The first part separates the relevant length scales and methods used to access them. At microscopic and mesoscopic scales, acoustic emission (AE) and microcompression studies reveal discrete dislocation avalanches and strain bursts that may be hidden in conventional macroscopic curves. At the specimen scale, local extensometry and digital image correlation (DIC) studies of the Portevin-Le Chatelier effect show how collective defect dynamics can organize into deformation bands and macroscopic stress serrations. Together, these approaches show that plastic flow may appear smooth only as an average response, while remaining intermittent at finer scales. The second part reviews direct CCA evidence, with emphasis on AE, stress-serration statistics, microplasticity, DIC, nanoindentation and small-scale deformation. A central conclusion is that serrated flow in CCAs should not be treated as a single phenomenon. Depending on chemistry, temperature, strain rate and microstructure, it may originate from dynamic strain aging, twinning, martensitic transformation, slip localization, or a combination of these mechanisms. Reported power-law-like distributions and exponents partly overlap with those known from simpler
crystals and
alloys, and the present evidence does not establish a distinct CCA-specific universality class. CCAs are therefore best viewed as tunable systems in which chemical disorder, short range order, phase stability and microstructure can modify the nucleation, arrest and synchronization of collective plastic events.
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All authors Michal Knapek, Tomáš Tayari, Kristián Máthis, Miloš Janeček
Materials Science · Cross-listed from cs.LG
Enhancing EBSD throughput of battery electrode materials using super-resolution generative adversarial networks
John Mangum, Andrew Glaws, Francois Usseglio-Viretta et al. (+2 more)
Quantitative microstructural characterization of Li-ion battery electrode materials using electron backscatter diffraction (EBSD) has been proven as a critical method for optimizing
cell performance. However, the inherently slow nature of EBSD can hinder the throughput of analyses needed for statistical representation of a material microstructure being developed. This work demonstrates a machine learning super-resolution framework using a generative
adversarial network (SRGAN) to significantly increase EBSD throughput. The SRGAN model was trained on EBSD data of LiNixMnyCozO2 (NMC) cathode particles to computationally enhance low-resolution
datasets and its performance is compared against classical interpolation methods across various upscaling factors (2x to 12x). Both qualitative image metrics and quantitative microstructural analysis verified that the SRGAN systematically outperformed classical methods, particularly in preserving small grains and maintaining realistic grain boundaries. We demonstrate that a 5x upscaling factor, corresponding to a 25x speed-up in acquisition time or a 25x larger field of view, is practical while maintaining acceptable accuracy in key metrics like grain size and shape. For instance, at 5x upscaling, relative errors were +5.7%, +8.2%, and -14.6% on grain area-equivalent diameter, grain maximum sphere-inscribed diameter, and grain boundary length, respectively. The SRGAN methodology developed in this work significantly enhances the efficiency of EBSD acquisition for more statistically robust microstructural
dataset, enabling EBSD as a high-throughput characterization tool for materials research and industrial process development.
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All authors John Mangum, Andrew Glaws, Francois Usseglio-Viretta, Steven Spurgeon, Donal Finegan
Materials Science
JANUS: A Multi-modal Foundation Neural Sampler for Disordered Materials
Denis Blessing, Mouyang Cheng, Maximilian Schebek et al. (+4 more)
Many problems in disordered materials require sampling beyond fixed composition and volume, where coupled changes in atomic identities and structure create a prohibitively expensive discrete-continuous sampling problem. Here we introduce JANUS, a
multimodal neural sampler that couples continuous and masked discrete
diffusion through an equivariant graph neural network trained directly from energy evaluations, without pre-generated
equilibrium data. In
benchmark Ising and isobaric $\Delta\mu NPT$
alloy systems, JANUS reproduces reference Monte Carlo
equilibrium observables and recovers free energies and phase behavior with more than three orders of magnitude fewer energy evaluations. In multicomponent
alloys, JANUS enables conditional steering toward prescribed chemical short-range order and enhanced bulk modulus and, when coupled to a large
language model evolutionary
agent, performs efficient inverse design for balanced optical and mechanical properties. In
semiconductors like silicon and diamond, JANUS explores vacancies and dopants spanning 15 elements in grand-canonical $\mu VT$ ensembles, recovers established defects including the silicon $E$ centre, and identifies new candidate defect pairs and triplets for
quantum engineering, including S-Ti in silicon and B-O-O in diamond, with deep in-gap states validated by hybrid-functional density functional theory. By unifying discrete site identities with continuous structural and volumetric relaxation, JANUS provides a foundation for thermodynamic sampling, characterization and inverse design of chemically disordered materials.
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All authors Denis Blessing, Mouyang Cheng, Maximilian Schebek, Jutta Rogal, Mingda Li, Carles Domingo-Enrich, Yuanqi Du
Materials Science
Local Structure and Dynamics of Three-Dimensional Covalent Organic Frameworks
Francesco Tavani, Saber Mirzaei, Jian Yin et al. (+6 more)
Resolving and controlling the local dynamical properties of covalent organic frameworks (COFs) remains a central challenge, particularly when assembled from large, flexible building units. Here, we combine synchrotron X-ray pair distribution function (PDF) analyses with machine learning-accelerated molecular dynamics (MD) simulations to resolve the local structure and dynamics of two three-dimensional imine-linked COFs, COF-682 {[(DHP)(TAM)]$_{imine}$}, assembled from 6,13-dihydropentacene (DHP) and tetrakis(4-aminophenyl)methane (TAM), and COF-612 {[(HBC-LA$_{12}$)(HAPT)$_2$]$_{imine}$}, assembled from nanographene dodecabenzaldehyde hexakis{[3,5-bis($p$-formylphenyl)-4,6-dimethoxyphenyl]}hexabenzocoronene (HBC-LA$_{12}$) and 2,3,6,7,14,15-hexa(4-aminophenyl)triptycene (HAPT). Validated against the experimental PDFs through ensemble-averaged calculations, the simulations show that the exposed $\pi$-surface and V-shaped geometry of the DHP linker endow COF-682 with enhanced local flexibility through face-to-face and offset $\pi$-stacking interactions differing in both their average interplanar separation and their ring-plane tilt angle. In contrast, the extended nanographene linker rigidifies COF-612 by maintaining the planarity of its fused cores, while the linker pendant aryl rings equip both COFs with enhanced librational ability. The simulations further provide quantitative measures of the translational and reorientational mobility of the linkers, revealing how local COF dynamics may be tuned by balancing non-covalent interactions and different degrees of aromatic rigidity. The PDF-MD experimental-computational approach holds promise as a general method beyond conventional crystallography to gain insights into the local properties of COFs with the aim of directing their dynamic function.
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All authors Francesco Tavani, Saber Mirzaei, Jian Yin, Yen-hsu Lin, Caden Myers, Cheng-Hung Lin, A. M. Milinda Abeykoon, Simon J. L. Billinge, Omar M. Yaghi
Materials Science
Anti-spin Laue groups: classification of anti-altermagnets and their representative minimal models
Colin Lange, Rodrigo Jaeschke-Ubiergo, Alexander Mook et al. (+1 more)
Anti-altermagnets exhibit odd-parity nonrelativistic
spin splitting, yet unlike even-parity altermagnets, their momentum-space
symmetries lack a reduced classification analogous to
spin Laue groups. Here, we introduce anti-
spin Laue groups, organized into three distinct classes, and identify 21 groups describing the odd-parity partial wave character of this unconventional class. Together with the 10
spin Laue groups of altermagnets, they complete the classification of nonrelativistic unconventional magnets with collinear momentum-space
spin polarization. Anti-
spin Laue groups also provide a many-to-one reduction of
spin space (point) groups by retaining only their action on the collinear momentum-space
spin polarization, thereby directly encoding the
symmetry-enforced nodal
spin-splitting character. Based on this we develop a systematic model-construction
algorithm yielding minimal, material-oriented four-band models. This framework places odd- and even-parity unconventional magnets on equal footing within a unified momentum-space
symmetry description.
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All authors Colin Lange, Rodrigo Jaeschke-Ubiergo, Alexander Mook, Jairo Sinova
Materials Science
Ab initio-based Deep-Learning Prediction of Carrier Mobility in Strongly Anharmonic Materials
Juan Zhang, Boheng Zhao, Yang Li et al. (+4 more)
Predicting charge transport in strongly anharmonic materials, particularly ultralow thermal conductors, remains a major challenge for first-principles methods. In such systems, perturbative treatments of electron-
phonon interactions and the harmonic
phonon picture often break down, necessitating non-perturbative approaches. The ab initio Kubo-Greenwood(aiKG) formalism provides a rigorous framework for evaluating temperature-dependent carrier transport beyond the harmonic approximation. Nevertheless, its practical application is computationally demanding because it requires large supercells, extensive statistical sampling, and extrapolation to the zero-frequency limit. In this work, we introduce an artificial-intelligence(AI)-assisted aiKG framework that incorporates the deep-learning
Hamiltonian model. By predicting the Kohn-Sham
Hamiltonian with sub-meV accuracy for supercells of up to 250 atoms, the model bypasses the costly iterative self-consistent field calculations while retaining first-principles reliability within the scope of effects captured by the training data. Using a strongly anharmonic thermal
insulator, potassium iodide(KI) as a
benchmark system, we demonstrate that the proposed approach enables efficient simulations of electronic structure and transport properties from a large supercell. The framework reproduces temperature-dependent carrier mobilities, spectral functions, and effective masses in close agreement with the underlying density functional theory while reducing computational cost to 10%. These results suggest that the AI-assisted aiKG framework can make non-perturbative transport calculations tractable for strongly anharmonic materials, opening a scalable route towards realistic simulations and accelerated discovery of new functional materials.
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All authors Juan Zhang, Boheng Zhao, Yang Li, Yong Xu, Hao Zhang, Kisung Kang, Matthias Scheffler
Materials Science · Cross-listed from physics.chem-ph
Universal Machine-learning Molecular Dynamics at the Speed of Empirical Potentials
Tiancheng Li, Jianming Xue, Linfeng Zhang et al. (+2 more)
No interatomic potential has offered universality across chemistry, near-first-principles accuracy and the speed of empirical potentials at once. Here we introduce DPA4C, an equivariant potential whose architecture and compressed CUDA operators are co-designed under deployment constraints to pursue accuracy and efficiency together. Five variants spanning a 49-fold parameter range form the high-throughput end of the measured accuracy–throughput frontier. The largest variant approaches the accuracy of the MACE-Omat models at about two orders of magnitude higher measured throughput. The most compact reduces the energy, force and stress errors of the fastest existing universal MLIP by 61.4%, 48.1% and 34.3% at 1.92 times its saturated throughput. All five variants complete multimillion-atom simulations on a single GPU and run molecular dynamics for 2.048 billion atoms on 1,024 16-GB NVIDIA V100 GPUs at 83.3–91.2% weak-scaling efficiency. Compared with the MEAM empirical potential, DPA4C-Nano reaches 1.8 and 2.5 times the saturated throughput in single-GPU scans on the same V100 hardware for diamond carbon and FCC copper, respectively. DPA4C therefore brings
quantum-trained universal accuracy into a regime of speed and system size previously associated with empirical potentials.
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All authors Tiancheng Li, Jianming Xue, Linfeng Zhang, Duo Zhang, Han Wang
Materials Science · Cross-listed from physics.chem-ph
Molecular Implementation of the Machine-Learned Skala Exchange-Correlation Functional in CP2K through GauXC
Franz Pöschel, Johann Pototschnig, Frederick Stein et al. (+6 more)
Machine-learned exchange–correlation (XC) functionals offer a route to improve Kohn–Sham density-functional theory without incurring the cost of explicitly correlated electronic-structure methods. Their use in production simulation codes, however, requires a well-defined mapping between the learned model and the host-code density representation. We formulate and implement a Skala-1.1 interface in CP2K through the external GauXC library. CP2K supplies the geometry, Gaussian basis,
spin-resolved atomic-orbital density
matrix, and communicator, while GauXC evaluates the XC energy, atomic-orbital potential
matrix, and available nuclear derivatives. The interface accepts both all-electron and valence-only density
matrices. The latter may arise from separable dual-space pseudopotentials or molecular effective-core potentials. Implementation errors are isolated from functional differences by comparing the Perdew–Burke–Ernzerhof (PBE) functional evaluated through GauXC with native CP2K PBE. The resulting interface gives consistent energies, forces validated against finite-difference total-energy checks, and force-based molecular-virial diagnostics for representative molecular cases. The dietGMTKN55
benchmark suite is evaluated with an all-electron Gaussian augmented plane-wave treatment for elements up to bromine and def2 effective-core potentials for the heavier elements. The resulting aggregate mean absolute deviation of 1.255 kcal/mol is within 0.012 kcal/mol of the corresponding Skala reference value of 1.243 kcal/mol. This work establishes a validated molecular implementation of Skala in CP2K through GauXC.
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All authors Franz Pöschel, Johann Pototschnig, Frederick Stein, Andreas Knüpfer, Thijs Vogels, Stefano Battaglia, Sebastian Ehlert, Jürg Hutter, Thomas D. Kühne
Materials Science
The role of weak interfaces in the tensile deformation and fracture of particle-filled polymers studied by phase-field model
Xu Chen, Ya Duan, Xiaoying Zhuang et al. (+1 more)
Weak particle-
matrix interfaces play a critical role in the tensile fracture of particle-filled
polymer composites, but how they govern progressive debonding, fracture localization, and the resulting changes in macroscopic mechanical properties remains insufficiently understood. In this study, a cohesive-zone phase-field model incorporating a hyperelastic
polymer matrix and a smeared interface is employed to investigate the coupled
evolution of interfacial debonding and
matrix fracture in particle-filled
polymer composites. The model is calibrated against and compared with uniaxial tensile responses of particle-filled polyurethane composites and then used to study how interfacial strength, interfacial fracture energy, and
matrix fracture properties affect the macroscopic stress-strain response and damage
evolution. The results show that weak interfaces can induce an intermediate softening regime in the stress-strain response, characterized by a reduced effective tangent stiffness and associated with distributed interfacial damage. Interfacial strength mainly controls the initiation of debonding, whereas interfacial fracture energy affects whether debonding can develop progressively in a distributed manner or rapidly localizes into a dominant crack band. Comparisons with well-bonded reference systems further demonstrate that weak interfaces may reduce the maximum stress but increase the strain at break by promoting distributed debonding around particles and delaying the formation of a dominant crack band. These findings clarify the dual role of weak interfaces and provide a mechanistic understanding of interface-controlled tensile failure in particle-filled
polymer composites.
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All authors Xu Chen, Ya Duan, Xiaoying Zhuang, Timon Rabczuk
Materials Science
Ultrafast order-selective electron imaging and spectroscopy
Jan Philipp Bange, Till Domröse, Claus Ropers et al. (+2 more)
Ultrafast pump-probe spectroscopies in energy and momentum have become indispensable for probing non-
equilibrium dynamics in
quantum materials, revealing pathways in ultrafast energy conversion and light-induced phase transitions. Different modalities uniquely access the coupled
lattice, charge, and
spin degrees of freedom that underpin the functionality of these materials. However, investigating technologically relevant nanoscale devices also requires high spatial resolution. Although electron microscopy provides nanometer-scale imaging, it frequently lacks the simultaneous ultrafast temporal resolution and spectroscopic specificity needed for such studies. In this perspective, we review recent advances in dark-field electron and photoelectron microscopy, focusing on two complementary techniques: femtosecond photoelectron momentum microscopy and ultrafast transmission electron microscopy. Their application enables comprehensive insights into the ultrafast dynamics of the electron,
lattice, and
spin subsystems. These order-selective electron imaging and spectroscopy techniques open broad scientific opportunities for a microscopic understanding of non-
equilibrium phenomena in
quantum materials, nanostructures and devices.
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All authors Jan Philipp Bange, Till Domröse, Claus Ropers, Stefan Mathias, Marcel Reutzel.
Materials Science
Detecting Magnetic Phase Transitions in Ion-Irradiated CrSBr Through Resonant Raman Scattering
Daria I. Markina, Alison Pfister, Priyanka Mondal et al. (+9 more)
Controlling
magnetic phases and accurately determining their transition temperatures are essential for the development of low-dimensional
magnetic materials. Here, we demonstrate that He$^+$ ion irradiation provides a versatile route for engineering
magnetic phases in layered CrSBr and establish temperature-dependent polarization-resolved Raman spectroscopy as a sensitive optical probe for identifying irradiation-induced
magnetic phase transitions. We reveal that the
magnetic response of the modified CrSBr is governed by both irradiation dose and
crystal thickness. The temperature
evolution of the Raman tensor elements resolves the antiferromagnetic transition in pristine CrSBr at T$_N \approx 132$ K as well as irradiation-induced
magnetic transitions at T$_C \approx 105-110$ K and T$_D \approx 40$ K corresponding to ferromagnetic and defect-related
magnetic phase transitions. Complementary magneto-optical measurements confirm the progressive suppression of antiferromagnetic order and the emergence of new defect-engineered
magnetic phases, including pure ferromagnetic behavior at high irradiation doses. These findings establish irradiated CrSBr as a platform for controllable
magnetic phase engineering while demonstrating polarization-resolved Raman spectroscopy as a rapid, non-destructive, and broadly applicable method for probing
magnetic phase transitions in van der Waals magnets.
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All authors Daria I. Markina, Alison Pfister, Priyanka Mondal, Lukas Krelle, Sai Shradha, Regine von Klitzing, Kseniia Mosina, Zdenek Sofer, Fangchao Long, Ulrich Kentsch, Shengqiang Zhou, Bernhard Urbaszek
Materials Science · Cross-listed from math.NA
A shifted energy barrier approach for phase-field modeling of tensile-dominated brittle fracture
Yaode Yin, Luigi Greco, Hongjun Yu et al. (+1 more)
The classical AT1 phase-field model contains an intrinsic energy barrier for crack nucle ation, which makes the predicted strength depend on the fracture toughness and the regularization length. For tensile-dominated brittle fracture, this barrier is shifted by mapping the Rankine criterion, evaluated on the effective stress, onto a state-dependent active-energy threshold. The prescribed tensile strength then controls crack nucleation, while the AT1 crack-density functional, stiffness degradation, and degraded stress response remain unchanged. Since the threshold depends on the current stress state, the field equations are derived from a restricted variational principle. A microforce formulation identifies the barrier shift as a dissipative resistance and provides the corresponding lower bound on the regularization length. In one-dimensional tension, closed-form solutions recover the prescribed peak strength and give a cosine-type localization profile that ap proaches the classical AT1 profile as the shift vanishes. Numerical examples show that, within the admissible range, the nucleation load is nearly insensitive to the regularization length and the predicted multiaxial nucleation states follow the Rankine envelope. Under overall compression, crack nucleation remains associated with local tensile stress concen trations. The formulation also captures the transition from strength-controlled failure for small flaws to the LEFM limit for large cracks.
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All authors Yaode Yin, Luigi Greco, Hongjun Yu, Simone Morganti
Materials Science
On the temperature dependence of the optical band gap in the material system of lithium niobate and lithium tantalate
Maximilian Henneke, Michael Ruesing, Nina A. Lange et al. (+13 more)
Lithium niobate and lithium tantalate see widespread use in optics and electronics, and are increasingly used for cryogenic applications. Despite their broad deployment, their optical band gap and its relation to the
crystal stoichiometry are not well characterised as a function of temperature. In this work, we study the optical absorption properties of congruent, stoichiometric, MgO-doped and Er-doped lithium niobate as well as congruent lithium tantalate across the temperature range between 7~K and 1000~K by means of optical transmission spectroscopy. Our results demonstrate that the difference of the optical band gap typically observed at room temperature between different stoichiometries is not primarily attributable to the intrinsic electronic structure, but rather to different electron-
phonon couplings and the average
phonon energies. Additionally, we exemplarily study the temperature shift of the 523 nm absorption line in Er-doped lithium niobate due to the increased interest in optically active dopants. To facilitate future analyses, we present the open-source software suite PhoQS-Treat (Tauc Regression Edge Analysis Tool), which enables automated Tauc regressions alongside additional analytical capabilities. This work advances the development of high-performance lithium niobate-based devices.
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All authors Maximilian Henneke, Michael Ruesing, Nina A. Lange, Timon Schapeler, Noah Spiegelberg, Ernst-Lukas Kuhlmann, Elke Beyreuther, Philipp Mues, Ludmila Eisner, Lukas M. Eng, Laura Padberg, Donat J. As, Klaus-Dieter Becker, Tim J. Bartley, Christine Silberhorn, Christof Eigner
Materials Science
Revisiting the topological properties of XMg2Bi2 (X = Ca, Sr, Ba, Yb and Eu)
Antoni Facca, Xujia Gong, Amar Fakhredine et al. (+2 more)
Density functional theory is known to underestimate band gaps in
semiconductors and to over- estimate inverted band gaps, frequently exaggerating the predicted size of the topological phase diagram of materials. Employing hybrid functionals and calculating the topological invariants, we revisit the topological properties of compounds crystallizing in the CaAl2Si2-type and demonstrate that the overestimation of the inverted band gaps is particularly pronounced in compounds with this
crystal structure. Among these, the class of XMg2Bi2 materials (X = Ca, Sr, Ba, Yb, and Eu) is topologically trivial for all considered cations. Our calculations show that these materi- als are narrow-gap
semiconductors with direct band gaps of 0.24-0.34 eV, slightly decreasing with increasing the atomic weight of the element X. We confirm this by applying uniaxial strain and hydrostatic pressure, confirming these results. We emphasize that the experimental observation of surface states alone is insufficient to establish nontrivial
topology, as trivial
semiconductors may host surface states without a surface Dirac point. Consequently, since these materials are intrinsi- cally topologically trivial, any experimentally observed topological signatures should be attributed to extrinsic effects such as doping or surface reconstruction. Our results underscore the importance of accurately treating electronic correlations when assessing topological character, even in materials containing heavy elements with strong
spin-orbit coupling, such as bismuth.
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All authors Antoni Facca, Xujia Gong, Amar Fakhredine, Carmine Autieri, Asiyeh Shokri
Materials Science
Linear and nonlinear optical responses in the chiral multifold semimetal BeAu: A quantum-geometric perspective
Babu Baijnath Prasad and Taisuke Ozaki
Chiral topological semimetals provide a natural platform for exploring how multifold band
topology and
quantum geometry manifest in optical and photovoltaic responses. BeAu is a chiral multifold semimetal hosting band crossings at $\Gamma$, $M$, and $R$ with Chern numbers $C_\Gamma=-4$, $C_M=-2$, and $C_R=+4$, respectively. In this work, we study the linear optical conductivity and second-order dc photocurrent responses of BeAu using fully relativistic first-principles calculations. The calculated interband linear optical conductivity, Re $\sigma_{xx}(\omega)$, is quantitatively reproduced by $(e^2/\hbar)\omega g_{xx}(\omega)$, showing that its spectral features are governed by the
photon energy factor and the variation of the
photon energy-resolved
quantum-metric spectral weight. The linear shift current conductivity is closely related to the symplectic connection, whereas the circular injection current susceptibility is governed by the transition-resolved product of Berry
curvature and the interband group velocity difference. At the Fermi level, the linear shift current conductivity reaches approximately -810 $\mu$A/V$^2$ at a
photon energy of 0.05 eV. Aligning the chemical potential with the multifold crossings strongly reshapes both responses, producing the largest linear shift current conductivity peak for $\mu=\mu_R$ and pronounced changes in the magnitude and sign of the circular injection current susceptibility. The circular photogalvanic trace is strongly
photon-energy and chemical-potential dependent and does not exhibit a broad quantized plateau, indicating competing multiband transitions. Our results establish a unified
quantum-
geometric description of the linear and nonlinear optical responses of BeAu and identify it as a promising platform for optoelectronic phenomena governed by multifold band
topology and
quantum geometry.
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Materials Science
The parity gap in crystal tensor prediction
Can Polat, Mustafa Kurban, Erchin Serpedin et al. (+1 more)
Crystal symmetry dictates whether a physical response tensor must vanish, establishing a direct test for machine learning predictions independent of property calculations. We derive the parity gap, a group-theoretic metric quantifying the piezoelectric tensor freedom permitted by a
crystal's proper rotation subgroup $SO(3)$ but eliminated by inversion
symmetry in $O(3)$. Across state-of-the-art equivariant neural network architectures, unconstrained $SO(3)$ models systematically predict forbidden non-zero responses matching the parity gap of each centrosymmetric
crystal class, while polar distortion paths dynamically map output responses to the loss of inversion
symmetry. Regression controls confirm that enforcing full $O(3)$ parity incurs no consistent accuracy cost across predictive tasks. Crucially, while training interventions using explicit zero labels reduce violation magnitudes, they leave residual forbidden outputs. Exact physical compliance instead requires structural enforcement through $O(3)$ representation design or explicit output antisymmetrization. The parity gap thus provides a unified framework to distinguish empirical error reduction from exact structural compliance with physical law.
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All authors Can Polat, Mustafa Kurban, Erchin Serpedin, Hasan Kurban
Materials Science
Thickness-dependent degradation and optical access in epitaxial 2H-MoTe2 protected by metallic capping layers
Wojciech Ryś, Iaroslav Lutsyk, Michał Piskorski et al. (+13 more)
We investigate degradation and surface protection of epitaxial 2H-MoTe2 films grown by molecular beam epitaxy on GaAs(111)B substrates. Using X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy, atomic force microscopy (AFM), Kelvin probe microscopy (KPM), Raman spectroscopy, and density functional theory (DFT), we examine the structural, chemical, and electronic
evolution of MoTe2 protected by Co and Ni capping layers. XPS shows that the metallic caps effectively suppress oxidation during short-term air transfer, while revealing a pronounced Te-rich near-surface composition. With time, the caps become increasingly difficult to remove, suggesting gradual interfacial bonding promoted by excess tellurium and defect-rich MoTe2 interfaces. AFM and KPM reveal pronounced thickness-dependent ageing, with ultrathin regions showing markedly different contact-potential
evolution from thicker films. DFT calculations support the sensitivity of work function and density of states to thickness and surface chemistry. Raman measurements through approximately 20 nm thick metallic caps demonstrate partial optical access to the protected material. Additional AFM and Raman observations suggest local formation of Te-rich nanostructures under
laser illumination or near mechanically damaged regions. These results provide practical guidelines for protecting, transferring, delaminating, and optically characterizing air-sensitive MoTe2 and related van der Waals materials.
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All authors Wojciech Ryś, Iaroslav Lutsyk, Michał Piskorski, Maxime Le Ster, Maciej Rogala, Paweł Dąbrowski, Paweł Krukowski, Katarzyna Ranoszek-Soliwoda, Jarosław Grobelny, Zuzanna Ogorzałek-Sory, Bartłomiej Seredyński, Wojciech Pacuski, Janusz Sadowski, Marta Gryglas-Borysiewicz, Karol Szałowski, Paweł J. Kowalczyk
Materials Science
Néel-order-dependent transverse transport in noncoplanar antiferromagnet $\text{MnTe}_{2}$
Qi Feng, Yilin Han, Yongkai Li et al. (+9 more)
Antiferromagnets hold appealing potential in next-generation spintronic devices with higher frequency and scalability, thanks to their alternating
spin orientations that cancel out net magnetization. However, the lack of a nonzero magnetization makes the detection of the
magnetic configuration of antiferromagnet difficult, hampering the applications of antiferromagnets. Here, we report a new transverse transport effect in noncoplanar antiferromagnet $\text{MnTe}_{2}$. This effect is antisymmetric in both
magnetic field and Néel order, but symmetric in its two indices. It can be understood in terms of the contribution induced by both
magnetic field and
geometric quantities, as confirmed by our theoretical calculations. Our discovery of a new Néel-order-dependent transverse transport effect provides opportunities to the advancing antiferromagnetic spintronics.
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All authors Qi Feng, Yilin Han, Yongkai Li, Yuqing Hu, Mo Tian, Qiuli Li, Huimin Peng, Jinrui Zhong, Zhiwei Wang, Zhi-Ming Yu, Junxi Duan, Yugui Yao
Materials Science
Three-temperature atomistic spin-lattice dynamics in LAMMPS: a moment-consistent, fluctuation-dissipation-correct extension and its validation on ultrafast demagnetization and all-optical switching of GdFeCo
Chun-Yeol You, Jiwan Kim and Dong-Hyun Kim
Atomistic
spin dynamics (ASD) codes like VAMPIRE simulate femtosecond-
laser-induced ultrafast demagnetization and all-optical switching (AOS) on a rigid
lattice; the
SPIN package of the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) instead propagates
spins and
lattice together, but until now could couple its
spin thermostat only to a single global temperature, precluding three-temperature (3TM) simulations. We present a validated 3TM extension with two new fixes: langevin/
spin/ttm, coupling the
stochastic spin bath to the local electron-temperature field of fix ttm; and moment/scale/
spin, supplying the per-atom moment-dependent ($1/\mu_i$) prefactor required for heterogeneous-moment systems, with deterministic terms scaling as $1/\mu_i$ and, as required by the fluctuation-dissipation
theorem,
stochastic noise scaling as $1/\sqrt{\mu_i}$. We validate the framework on single-species
benchmarks-precession, the bcc-Fe Curie curve, a continuous demagnetization-remagnetization-precession trajectory, and a
lattice-strain acoustic-
phonon pulse unavailable to
spin-only ASD codes-then on heat-induced AOS of GdFeCo with literature parameters (Radu/Ostler exchange constants, moments, and damping). The corrected integrator reproduces the experimentally reported transient ferromagnetic-like sublattice
alignment, field-insensitive thermal switching, a switching probability approaching unity across a genuine 8x8 literature damping phase diagram, a non-monotonic critical-cooling-duration boundary that disappears above $T_e^0 \approx 2000 \text{ K}$, a composition-dependent switching window centered on angular-momentum compensation, and convergence in system size with monotonic, physical damping dependence. These results establish LAMMPS as a quantitatively validated platform for three-temperature
spin-
lattice simulations of ultrafast magnetism.
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Materials Science · Cross-listed from cond-mat.str-el
Universal thermal breakdown of polaron coherence in one, two, and three dimensions
Jeet Shannigrahi, Janez Bonča and Mona Berciu
How a polaron loses its quasiparticle coherence with increasing temperature is a long-standing open problem. Holstein addressed it in 1959 only in the extreme antiadiabatic, strong-coupling limit, while more recent numerically exact approaches are largely restricted to one dimension. Here we solve this problem on square and simple cubic
lattices across the weak-, intermediate-, and strong-coupling regimes. We show that the polaron effective mass $m^*$ and inverse lifetime $1/\tau$ increase monotonically with temperature until, at $T \sim 0.5\,\Omega$, the quasiparticle peak dissolves into a broad incoherent thermal continuum. The
phonon frequency $\Omega$ therefore defines a universal coherence scale, independent of dimensionality and coupling strength, validating Holstein's prediction far beyond the regime in which it was derived. These results follow from a finite-temperature generalization of the Momentum Average (MA) approximation, yielding a closed-form, diagrammatically derived self-energy that is asymptotically exact in the strong-coupling limit at all temperatures.
Benchmark comparisons demonstrate excellent quantitative agreement of the resulting 1D spectral functions with the numerically exact Variational Exact Diagonalization-Finite-Temperature Lanczos Method (VED-FTLM) and finite-$T$ Density
Matrix Renormalization Group (DMRG).
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Materials Science
Operando Raman probing of mode selective electron phonon coupling in two dimensional halide perovskites
Tufan Paul, Helena Boom, Lilian Skokan et al. (+8 more)
Electron
phonon coupling governs charge transport, carrier relaxation, and polaron formation in halide perovskites, yet its microscopic origin in low dimensional systems remains poorly understood. Here, we combine operando, bias dependent Raman spectroscopy with density functional theory (DFT) calculations to directly probe carrier
lattice interactions in two-dimensional Ruddlesden Popper perovskites,(PEA)$_2$PbI$_4$ and its fluorinated analogue, (PEA-F)$_2$PbI$_4$. Under applied electric fields, both systems exhibit mode-selective Raman linewidth broadening predominantly near 100 cm$^{-1}$, whereas other
phonon modes remain largely unaffected, revealing highly selective coupling between injected carriers and specific
lattice vibrations. DFT calculations identify these modes as hybrid organic inorganic vibrations involving coupled motion of the organic spacer and symmetric Pb I equatorial stretching, rather than purely inorganic
phonons. Fluorination fundamentally reconstructs the vibrational landscape by modifying molecular packing,
crystal symmetry, and organic inorganic coupling, resulting in changes to the
phonon density of states, longer
phonon lifetimes, and an enhanced carrier mediated
lattice response. Notably, electrical bias produces opposite
phonon lifetime
evolution in thin films and single
crystals: the
phonon lifetime decreases by approximately 17 to 22% in thin films but increases 20 to 26% in single
crystals. These contrasting responses demonstrate that structural order plays a fundamental role in determining carrier
phonon interactions and
phonon relaxation pathways in two-dimensional halide perovskites.
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All authors Tufan Paul, Helena Boom, Lilian Skokan, Viren Tyagi, Mostafa Shagar, Aditi Sahoo, Silvia Colella, Geert Brocks, Andreas Ruediger, Shuxia Tao, Emanuele Orgiu
Materials Science
Room-temperature ferroelectrically switchable quantum geometry in few-layer WTe2 for complementary in-memory computing
Ruihan Wang, Pengfei Wang, Haoyun Chen et al. (+10 more)
Quantum geometry, describing the inherent
geometric structure of electron wavefunctions in momentum space, transcends the traditional charge degree of freedom and provides a novel physical basis for information encoding and processing. The key to such new computing paradigms is the non-volatile electrical programming of
quantum geometric states at room temperature, which, however, has not been established. Here, we demonstrate ferroelectrically switchable
quantum geometry in few-layer WTe2, which uniquely enables complementary convolutional processing. By employing the intrinsic coupling between ferroelectric polarization and
quantum geometry in few-layer WTe2, we show that the second- and third-order nonlinear anomalous Hall effects (NLAHE) can be deterministically and electrically switched in a nonvolatile and correlated manner. The switching is robust at room temperature for ~104 cycles and retention of ~105 s. Furthermore, leveraging the opposite switching behaviors of second- and third-order NLAHE at room temperature, we demonstrate complementary in-
memory computing and implement a hardware-level complementary convolution kernel. This kernel overcomes the inherent directional specificity of conventional convolutional networks and achieves a texture recognition accuracy of 98%, thereby illustrating a viable pathway towards physics-native computing through exploiting exotic physics in
quantum materials.
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All authors Ruihan Wang, Pengfei Wang, Haoyun Chen, Yunze Peng, Bingyan Liu, Junlin Xiong, Xueyuan Zhang, Chen Pan, Xin Chen, Shengyuan A. Yang, Shi-Jun Liang, Feng Miao, Peng Song
Materials Science
Room-Temperature Polarity Control of the Anomalous Nernst Effect in a High-Magnetic-Anisotropy Topological Nodal-Line MnAlGe
Nanhe Kumar Gupta, Keisuke Masudaa, Masaaki Kakoki et al. (+7 more)
Controlling the polarity of anomalous Nernst thermopower is a promising strategy for enhancing the performances of thermoelectric applications. However, realizing such control at room temperature (RT) in topological ferromagnets with high
magnetic anisotropy (Ku) remains challenging. Here, we report RT polarity control of the anomalous Nernst effect (ANE) in quasi-two-dimensional nodal-line MnAlGe epitaxial thin films through Al/Ge compositional tuning while preserving robust high Ku. This polarity reversal originates from intrinsic Berry
curvature contributions modulated by sublattice-selective carrier doping, as supported by
spin-resolved electronic band structure analysis and hard X-ray photoemission spectroscopy. To demonstrate the practical feasibility, we also fabricated a meander-structured device combining MnAlGe with positive and negative polarity enhanced the thermoelectric output. Our results demonstrate that tuning the Fermi level relative to the nodal-line electronic structure while preserving high Ku enables controllable ANE polarity reversal within a single material, providing a route toward RT transverse thermoelectric devices.
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All authors Nanhe Kumar Gupta, Keisuke Masudaa, Masaaki Kakoki, Benugopal Bairagya, Satoki Tazawaa, Weinan Zhoua, Hirofumi Sutoa, Ryo Toyama, Akio Kimura, Yuya Sakuraba