Materials Science · Cross-listed from cs.CL
A literature-guided descriptor-based framework for filtering composition search spaces
Lei Zhang and Markus Stricker
Scientific literature contains latent knowledge about materials behavior, but much of this knowledge is expressed through words, contexts, and recurring associations rather than explicit design principles. This raises a central question: how can large-scale scientific corpora be used for practical problems in materials discovery? Here, we present a literature-guided descriptor-based filtering framework for reducing composition search spaces. For a given performance metric, the framework selects two descriptors from a filtered vocabulary in a literature-trained word
embedding model and uses the selected descriptors to construct a Pareto-based filter for candidate compositions. Across the evaluated performance metrics and composition search spaces, the framework filters out an average of 74.27% of the candidate compositions, with an average best-value error of 1.93% relative to experimental measurements. Compared with expert-chosen and random descriptors, our performance metric-dependent descriptors provide a more controlled balance between retained fraction and best-value error. These results show that literature-derived
embeddings can support intuitive and reproducible filters for narrowing candidate composition spaces while preserving high-performing compositions.
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Materials Science
Full Minimal Coupling All-Electron Real-Time TDDFT for X-Ray-Matter Interactions
Daniel Schacher, Tod A. Pascal, Craig P. Schwartz et al. (+1 more)
Standard real-time time-dependent density functional theory (RT-TDDFT) couples light to matter through a spatially uniform (dipole) vector potential, an approximation that breaks down in the X-ray regime, where the
photon wavelength approaches interatomic scales. We present an all-electron, numeric-atom-centered-orbital implementation of full minimal coupling in FHI-aims that retains the spatial structure of the vector potential in both the paramagnetic and diamagnetic couplings, implements a reciprocal-space-resolved current diagnostic, and extends the propagation to periodic systems through a perturbative
photon-momentum sideband coupling that recovers the density response at the
photon wavevector. Four
benchmarks ranging in energy from 100 eV to 5 keV validate the implementation and exercise its reach. The retained
photon momentum proves physically consequential throughout, from measurable beyond dipole corrections to the enabling of channels forbidden in the dipole limit. On an all-electron footing, the implementation lays the groundwork for a general ab initio treatment of X-ray light-matter interaction across molecules, surfaces, and solids.
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All authors Daniel Schacher, Tod A. Pascal, Craig P. Schwartz, Keith V. Lawler
Materials Science · Cross-listed from physics.comp-ph
Highly Parallel Real-Space Random Phase Approximation Using Lanczos Quadrature and Interpolation
Abir Haque, Edmond Chow, Shikhar Shah et al. (+3 more)
We present a highly parallelizable,
matrix-free, real-space method for computing the random phase approximation (RPA) correlation energy within Kohn-Sham density functional theory. In particular, we avoid the explicit construction and eigen-decomposition of the response function
matrix and use Lanczos quadrature to evaluate the trace of a
matrix function on a real-space grid. We also show it is possible to exploit the spatial smoothness of the RPA correlation energy density in real-space to reduce computational cost. Specifically, we compute the energy density on a coarse grid, then reconstruct an approximation to the full, fine grid via interpolation. We implement this formulation within the SPARC electronic structure package and demonstrate its convergence, accuracy, agreement with planewave results, and scaling. Interpolation can enable an $8\times$ reduction in the computational prefactor. Given the embarrassingly parallel nature of the proposed method, we achieve near-ideal speedups and near-cubic scaling, thus allowing us to compute the RPA correlation energy for a silicon system with 256 valence electrons at chemical accuracy in less than 30 minutes on 4,096 CPU cores.
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All authors Abir Haque, Edmond Chow, Shikhar Shah, Andrew J. Medford, John E. Pask, Phanish Suryanarayana
Materials Science
Domain-wall energy governs coercivity in ordered and disordered additively manufactured Fe–49Co–2V
Dennis Boakye and Chuang Deng
Additively manufactured soft-
magnetic Fe–Co is consistently harder than wrought material of the same composition, and controlling that excess is the central obstacle to printing electrical machines from these
alloys. The literature attributes it to B2 chemical ordering, untested because the anisotropy of the ordered state had not been measured for this
alloy and because printed material had never been compared with wrought material at matched grain size. In this study we supply both. Calibrating on wrought Fe–49Co–2V at a known order parameter fixes the ordered-state domain-wall energy and caps every pinning channel independent of grain size. Ordering then falls orders of magnitude short of the measured excess, and a tenfold change in antiphase-domain size leaves coercivity unchanged. What ordering controls is the wall energy, and that effect is small and bounded. The excess is retained defect content, which moves process optimization from post-build annealing to in-build defect control.
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Materials Science
Breaking the Wiedemann-Franz limit in thermoelectrics via separated flat bands
Illia Serhiienko, Fabian Garmroudi, Stefan Enzner et al. (+3 more)
Controlling the charge and
spin degrees of freedom of electrons in solids has been at the heart of condensed-matter science for centuries. One hallmark of metallic conduction is the Wiedemann-Franz law which implies that a moving charge carries
entropy. Despite centuries of dedicated research, disentangling charge and heat transport has remained an unsolved issue so far. Here we present a direct route to reduce thermal conductivity of conduction electrons with respect to their electrical conductivity via energy-dependent scattering. By constraining electronic transport to a boxcar-type distribution asymmetrically around the Fermi energy, a large Seebeck coefficient and electrical conductivity can be realized simultaneously while electronic heat conduction is suppressed. Based on the case of monolayer Ni$_3$In, which comprises two flat bands around the Fermi energy, we propose flat-band systems as a promising, tunable platform for scattering phase space engineering. Besides this novel approach, our large-scale assessment of $\approx 5\times 10^4$ data sets in a 'Wiedemann-Franz plot' of $zT$ vs. $S^2$ provides an effective tool to identify reports of $L\ll L_0$ from literature - pointing towards either new and interesting physical mechanisms - or overlooked measurement artifacts.
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All authors Illia Serhiienko, Fabian Garmroudi, Stefan Enzner, Izem Dural, Giorgio Sangiovanni, Andrej Pustogow
Materials Science
Two-Dimensional Materials toward CMOS-Compatible Scalable Quantum Hardware
Mara Lieberegts and Ye Wang
Manufacturability is one of several constraints on developing solid-state
quantum processors, along with
qubit performance, control, connectivity, cryogenic operation, and fault tolerance. Chemical residues, structural disorder, and non-uniform interfaces introduced during fabrication can compromise
qubit coherence. Two-dimensional (2D) materials, with their atomically thin
crystals and van der Waals interfaces, offer routes to address some of these challenges. Their concurrent development as next-generation CMOS channel materials motivates an examination of whether relevant processes can be transferred to
quantum chips. This Perspective evaluates the opportunities and limitations of 2D materials for CMOS-compatible
quantum hardware.
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Materials Science · Cross-listed from cond-mat.str-el
Charge order before superconductivity in the doped kagome Dirac spin liquid
Yasir Iqbal
Doping a
quantum spin liquid is expected to produce a
superconductor. We show that for the Dirac
spin liquid on the kagome
lattice the doped charge orders first. The charge is carried by a chargon doublet whose two gauge components are degenerate on the square and triangular
lattices, and the kagome
lattice, as the line graph of the honeycomb
lattice, splits them. One component disperses and condenses in four valleys. The other has flat lowest bands and stays empty over a window in the bare mass whose width, $(\sqrt6-1)t$, follows from the band structure alone. Within that window, in the mean-field chargon theory constructed from the projective
symmetry group of the
spin liquid, the doped state forms charge and loop-current
crystals with the electromagnetic U(1) unbroken and no superconductivity. Pairing requires a gapped descendant of the
spin liquid as the parent and then takes the form of a pair-density wave, with no uniform $d+id$ channel at leading order and none at any order for the
crystals at the $M$ point. The predicted charge order is odd under the twofold rotation and has no cubic invariant, which distinguishes it from the charge order of the kagome metals.
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Materials Science
An Open-Source Hardware and Software Toolkit to Enable Agentic RHEED-Guided Thin-Film Synthesis
Asraful Haque, Christopher M. Rouleau, Rama K. Vasudevan et al. (+1 more)
Reflection high-energy electron diffraction (RHEED) provides rich information about evolving surfaces during thin-film growth, but non-automated, operator-dependent
alignment and fragmented analysis workflows limit its potential in fully autonomous synthesis. Here, we present an open-source hardware and software toolkit that makes RHEED control and quantitative analysis accessible to operators and artificial intelligence (AI)
agents. Demonstrated on a pulsed
laser deposition system, the toolkit provides programmable electron-optics control, automated beam
alignment and rocking-curve acquisition, and a training-free method for crystallographic azimuthal
alignment. The auto RHEED application extracts structural and growth-related observables through shared graphical and programmatic interfaces, including a Model Context Protocol (MCP) server. An
agent-driven demonstration shows how natural-
language requests can guide the selection, configuration, and execution of quantitative analyses. An extensible adapter interface streamlines the incorporation of community-developed methods for AI analysis and RHEED simulation as they emerge, supported by Markdown implementation guides designed for AI coding
agents. These capabilities support complementary descriptions of surface
evolution through physical measurements and learned image representations while providing a practical route for incorporating new computational methods. Together, these tools reduce barriers to automated and agentic RHEED measurements and establish a foundation for future agentic control of thin-film synthesis guided by the evolving surface.
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All authors Asraful Haque, Christopher M. Rouleau, Rama K. Vasudevan, Sumner B. Harris
Materials Science · Cross-listed from physics.chem-ph
Toward Predictive Hydride Bond Energetics with Neural-Network Wavefunctions
Aqsa Shaikh, Lubos Mitas, P. Ganesh et al. (+1 more)
Accurate prediction of transition-metal hydride (TM-H) bond dissociation energies (BDEs) remains challenging because of strong electron correlation, relativistic effects, and nuclear
quantum contributions. Here, we assess the performance of neural-network variational Monte Carlo (NN-VMC) based on the Psiformer ansatz for systems with increasing complexity (LiH, OH, TiH and NiH), and compare it against CCSDT(Q)/CBS as well as available theoretical and experimental data. Throughout this study, both NN-VMC and ab initio calculations employ a common ccECP
Hamiltonian to enable tractable and consistent comparisons. To reduce finite-training errors, we introduce complementary zero-variance and infinite-step extrapolation schemes. For LiH and OH systems, NN-VMC yields total energies that differ within sub-milli Hartree compared to CBS extrapolated ab initio results and the BDE differences remain under 2$\sigma$. In case of Ti and TiH, the variational NN-VMC energies at the end of training are already consistent with CCSD(T)/CBS, while post-training extrapolation systematically closes the gap towards the CCSDT(Q)/CBS results. In contrast, NiH provides a stringent test of wavefunction expressivity, where increasing the number of determinants in NN-wavefunction ansatz improves the recovered correlation energy. The comparison of NiH BDE reveals that, while the existing theoretical predictions cluster into distinct high and low BDE groups, the broad scatter in available experimental data prevents a definitive assessment of the most accurate theoretical approach. This work demonstrates that NN-VMC with ccECPs
Hamiltonian provides a competitive framework for quantitative prediction of main-group and early TM-H energetics, while identifying late TM-H as an important
benchmark for future developments in neural-network wavefunctions and electronic structure theory.
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All authors Aqsa Shaikh, Lubos Mitas, P. Ganesh, Jaron T. Krogel
Materials Science
High-Temperature Hydrogen Sensors Based on Gallium Oxide Heterojunction Diodes
William A. Callahan, Kingsley Egbo, Anna Sacchi et al. (+5 more)
Long-term, high temperature operation of Ga2O3 devices is a crucial hurdle that must be overcome before widespread adoption of the technology can be achieved, but is largely absent from the overall body of work. Demonstrations up to this point show devices are either limited by material or dopant instability that leads to performance degradation with time. Herein, Ga2O3-based hydrogen sensors employing Pt Schottky and Cr2O3/Ga2O3 p-n diodes (Mg- and N-doped) were fabricated and evaluated for long-term stability at 600C for 800-1,800 hours, with cyclic exposure to N2 and low-concentration H2 (500-1,500 ppm). Transient current density (measured at -0.1 V) and periodic J-V characterization were used to track performance. Despite gradual declines in sensor signal and sensitivity, devices distinguished hydrogen concentrations throughout weeks of operation. Degradation was architecture-dependent: Cr2O3:Mg degraded gradually, consistent with known Mg migration; the Pt Schottky diode showed dramatic changes after 1,000 hours; and Cr2O3:N showed the lowest but most stable performance before failing at 800 hours. Thermionic emission and Lambert W-based modeling confirmed hydrogen exposure reduces interfacial barrier height via a
proton-induced dipole mechanism common to both diode types. TEM of aged Pt Schottky diodes revealed Pt grain growth and microvoid formation as key degradation mechanisms. TOF-SIMS confirmed nitrogen dopants remain confined to the Cr2O3:N layer, supporting N-doping as a stable, lower-performance alternative to Mg-doping
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All authors William A. Callahan, Kingsley Egbo, Anna Sacchi, Michelle Smeaton, Michael Walker, Anna Staerz, Ryan O'Hayre, Andriy Zakutayev
Materials Science · Cross-listed from cond-mat.str-el
Chiral Antiferromagnetism from Momentum-Space Resonance in a 2D Semiconductor
R. Okuma, T. Ikenobe, Y. Fujisawa et al. (+28 more)
Understanding the principles governing the emergence of chiral
quantum phases is a fundamental challenge, not only for uncovering new mechanisms of
quantum-state formation but also for realizing giant electronic responses and transport phenomena arising from chirality and
topology. While Fermi-surface instabilities in metals can stabilize complex ordered states through multiple competing scattering channels, their microscopic origin is often obscured by the complexity of the underlying electronic structure, limiting the development of general microscopic design principles. Here, we introduce a complementary strategy based on the simplicity of
semiconductor band extrema. Using the layered van der Waals
semiconductor GdGaI, whose low-energy electronic structure consists of simple electron and hole valleys, we discover the spontaneous emergence of an intertwined chiral triple-$q$ antiferromagnetic state accompanied by a cooperative reconstruction of the electron-hole band edges, beyond the conventional expectation of a single-$q$ ground state. This collective reconstruction generates substantial momentum-space Berry
curvature, giving rise to a pronounced spontaneous anomalous Hall effect despite the semiconducting character and negligible net magnetization. Remarkably, this chiral state is realized within an atomically well-defined ($\approx2a$), topologically nontrivial
magnetic texture, showing that such collective
quantum states can emerge at an exceptionally small length scale from a simple two-dimensional
magnetic semiconductor. More broadly, our results introduce a remarkably simple design concept for chiral
quantum matter: using simple
semiconductor band extrema as building blocks for resonance-like interplay in momentum space, providing a route to Berry
curvature, topological transport, and emergent
quantum phases.
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All authors R. Okuma, T. Ikenobe, Y. Fujisawa, K. Yamagami, H. C. H. Wu, T. Nakamura, Y. Ihara, H. Ishikawa, H. Suwa, H. Ishizuka, Y. Akagi, T. Kaneko, C. H. Hsu, Y. Obata, N. Tomoda, M. Dronova, K. Nagasawa, H. Saito, D. Ueta, H. Sagayama, J. Yamaura, M. Arita, K. Yogendra, S. Ideta, K. Kindo, T. Nakajima, S. J. Blundell, T. Kondo, K. Shimada, Y. Okamoto, Y. Okada
Materials Science
Microstructure-Resolved Impedance Modeling of Solid-State Batteries
Kaniza Islam, Chengyin Wu, Noriko Katsube et al. (+1 more)
Solid-state batteries (SSBs) with solid electrolytes (SEs) are attracting substantial investment from the automotive industry to enable fast-charging and safer next-generation electric vehicles. The microstructure of the SE critically affects the battery performance. Electrochemical impedance spectroscopy (EIS) is a powerful, non-destructive probe of charge-transfer and transport processes within SEs and across electrode/SE interfaces but quantitatively connecting measured impedance spectra to the underlying microstructural features remains an open modeling challenge. Here we present a modeling framework that predicts the microstructure-resolved impedance response of a Li/Li6PS5Cl/Li symmetric
cell. Taking the Li6PS5Cl SE microstructures from phase-field sintering simulations, we find that increasing porosity shifts the Nyquist semicircle to higher impedance while improved inter-particle contact reduces it, and that impedance decreases monotonically as sintering proceeds. We also isolate the effect of solid electrolyte interphase (SEI) formation: grain boundaries raise impedance only slightly, but SEI volume fraction, and the conductivity of each SEI phase (Li2S, Li3P, LiCl), both strongly affect it. A realistic multi-phase SEI increases interfacial impedance by about two orders of magnitude compared with a grain boundary only network. We further demonstrate that the same pipeline can operate directly on experimental micrographs by extracting pixel-level phase information with AI-assisted image segmentation and using it to predict an impedance spectrum, illustrating a path toward quantitative microstructure-impedance correlations grounded in real, imaged SE microstructures.
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All authors Kaniza Islam, Chengyin Wu, Noriko Katsube, Yanzhou Ji
Materials Science
How Accurately Can We Describe Spin Crossover?
Angel Albavera-Mata, Daniel Mejía-Rodríguez, Niranjan Govind et al. (+3 more)
The complicated physicochemical properties of metal complexes that exhibit thermal
spin crossover make it difficult for routine electronic structure calculations to yield an accurate transition temperature prediction, $T_{1/2}$. The difficulty lies in the intricate connection between the
spin-crossover energy, which is a molecular spectroscopic property, and $T_{1/2}$, a condensed phase property. Here we show how to obtain
spin-crossover energies systematically by reverse engineering of experimental $T_{1/2}$ data. The protocol is based upon fitting the range separation parameter, $\omega$, in the hybrid LC-$\omega$PBE density functional to reproduce the experimental $T_{1/2}$ values for a series of metal complexes. We provide insights into the sources of variations of at least $\pm 15$ kJ mol$^{-1}$ found from common exchange and correlation functionals by comparing their performance against our reference data. By analysis of the sensitivity of transition temperatures to $\pm 1$ % shifts in the range separation parameter, we determined a typical uncertainty of $\pm 50$ K for them, and a $\pm 2$ kJ mol$^{-1}$ uncertainty in the extracted
spin-crossover energies due to $\pm 1$ % variations of $T_{1/2}$. Lastly, we present results from the high-level, all-electron coupled cluster method for eight of the smaller molecules in the reference data set, and discuss the influence of the truncation of the excitation series upon the
spin state energies.
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All authors Angel Albavera-Mata, Daniel Mejía-Rodríguez, Niranjan Govind, Ajay Panyala, Richard G. Hennig, S.B. Trickey
Materials Science
Proximity-induced charge density waves in a moiré heterobilayer
Christopher T. S. Cheung, Arash A. Mostofi and Johannes Lischner
Twisted heterobilayers of two-dimensional materials have emerged as a platform for studying emergent phases of matter. In this work, we investigate charge density waves (CDW) in a twisted NbSe$_2$/MoSe$_2$ bilayer using first-principles calculations. We observe CDW formation in both layers, even though MoSe$_2$ does not feature a CDW in its monolayer form. Moreover, we find that the CDW is highly non-uniform with filled-center, hollow-center and hexagonal CDWs coexisting in the moiré unit
cells of both layers. We assess different mechanisms of CDW formation in the MoSe$_2$ layer and conclude that the dominant one is the steric repulsion between Se atoms across the van der Waals gap. The strength of this effect is highly sensitive to the interlayer separation, which explains why the CDW amplitude in the MoSe$_2$ layer depends strongly on the local stacking arrangement. Our work demonstrates that novel broken-
symmetry phases can be induced in twisted heterobilayers through proximity effects.
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Materials Science · Cross-listed from cond-mat.mes-hall
Spatiotemporal programming via asymmetric dielectric engineering for nonvolatile 2D optoelectronics
Xiaoguang Luo, Xiaolong Zhang, Honglei Chen et al. (+11 more)
Ambipolar two dimensional (2D)
semiconductors integrated with floating-gate architectures offer a promising platform for nonvolatile, reconfigurable electronics. However, the switching between p-n and n-p junction polarities has conventionally required complex multi-gate designs, hindering the scalability and integration density. Here, we demonstrate a spatiotemporal programming strategy using a dual-floating-gate architecture with a
symmetry broken tunneling dielectric. An asymmetric dielectric stack creates distinct tunneling thresholds for two floating gates, enabling a single input gate to encode spatial doping profiles in the 2D channel via defined voltage pulse sequences. We achieve on demand, nonvolatile, and reversible switching between p-n and n-p configurations with excellent retention and endurance. The reconfigurable homojunction serves as a multifunctional platform for logic encoding, rectification, photodetection, and in sensor computing. This work establishes a design paradigm that replaces spatial input complexity with spatiotemporal programming, paving the way for high-density, multifunctional intelligent hardware.
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All authors Xiaoguang Luo, Xiaolong Zhang, Honglei Chen, Jiaming Wang, Fan Liu, Jiongtao Zhang, Junqiang Zhang, Yihan Yin, Jinpeng Xu, Lei Ying, Renjing Xu, Yingchun Cheng, Xuetao Gan, Wei Huang
Materials Science
Freestanding Antiferromagnetic Oxide Membranes: Synthesis and Characterization of Cr$_2$O$_3$
Ella Blake, Tiffany C. Wang, Yi Cui et al. (+9 more)
Antiferromagnetic (AFM)
insulators stand out as a promising class of materials for fast switching, energy-efficient
magnon-based technology, but our understanding of how to tune these properties with the
lattice remains limited. As an AFM
insulator with strong magnetoelectric response, Cr$_2$O$_3$ membranes stand out as a promising platform to explore multi-modal tunability via strain. However, fabricating these membranes is challenging due to the scarcity of etchable sacrificial layers with compatible
lattice constants and sufficient surface quality. We address this issue by utilizing La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) as a sacrificial layer, enabling successful fabrication of millimeter-scale Cr$_2$O$_3$ membranes. Substrate-free characterization reveals that strain due to the
lattice mismatch during growth is released by the formation of small polycrystalline domains, preserving single-crystalline order over ~90% of the membrane area. Bulk-like structural properties are confirmed by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and second-harmonic generation spectroscopy. Platinum Hall measurements reveal an above-room-temperature N$\'e$el transition. These results establish Cr$_2$O$_3$ membranes as a viable platform for strain-tuning antiferromagnetism and magnetoelectricity.
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All authors Ella Blake, Tiffany C. Wang, Yi Cui, Minyong Han, Yinchuan Lv, Christopher T. Parzyck, Octave Duros, Yan Che, Matthias C. Hoffmann, Wei-Sheng Lee, Yi Cui, Harold Y. Hwang
Materials Science
Twin Domains in Van der Waals Quaternary Oxides
Dorothée S. Mader, Niels Brumby, Xiaosheng Yang et al. (+10 more)
Optical anisotropy is the basis for many intriguing phenomena in van der Waals materials, including
hyperbolic polaritons and extreme birefringence. Stacking and twisting van der Waals materials along the out-of-plane direction emerged as a powerful route to tailor this anisotropy, but designing lateral interfaces remains a challenge. Here, twin domains are reported in the van der Waals quaternary oxides MgTeMoO$_6$, MnTeMoO$_6$, ZnTeMoO$_6$, and CoTeMoO$_6$ - materials that possess strong in-plane optical anisotropy and second-order nonlinearity. The domains naturally form in their orthorhombic
crystal structure and extend over hundreds of micrometers. It is proposed that this stability is achieved by the domain wall acting as a diagonal mirror plane in the
crystal structure, parallel to the (1-10) or (110)
crystal planes, resulting in nearly opposite birefringence between domains. This hypothesis is experimentally confirmed by determining the angle between the
crystal axes of neighboring domains using polarization-resolved optical microscopy, infrared-visible sum-frequency generation microscopy, and transmission electron microscopy. The latter further allowed an estimate of the domain wall thickness. Overall, the observation of twin domains with orthogonal optical anisotropy opens new routes to use van der Waals quaternary oxides for birefringent waveguiding, polariton steering, and frequency conversion applications.
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All authors Dorothée S. Mader, Niels Brumby, Xiaosheng Yang, Nele Stetzuhn, Eduardo Ortega, Christian Carbogno, Katayoun Gharagozloo-Hubmann, Sebastian F. Maehrlein, Martin Wolf, Kirill Bolotin, Peining Li, Niclas S. Mueller, Alexander Paarmann
Materials Science
The Case Against Hall-Petch Hardening in High Entropy Carbide Ceramics
Ali Sarikhani, Ana C. Feltrin, Gregory E. Hilmas et al. (+5 more)
Grain size is often used with the Hall-Petch relationship to justify differences in hardness in ceramic materials. Herein, hardness does not vary systematically with grain-size for fully dense, single-phase (Cr,Mo,Ta,V,W)C1-{\delta} high
entropy carbide ceramics for grain sizes that varied by a factor of three. Fully dense, single-phase ceramics with grain sizes from 9.3+/-0.3 to 28.8+/-0.7 microns exhibited a pronounced indentation size effect, with Vickers hardness decreasing from ~28-30 GPa at 0.49 N to ~20-21 GPa at 9.81 N, and Berkovich nanohardness ranging from 26 to 30 GPa at 10 mN. However, at a given load, hardness remained within a narrow range across the grain-size series, and no consistent Hall-Petch dependence was resolved. The lack of grain-size dependence likely indicates that the deformation volume sampled by the indenter was not controlled by grain-boundary interactions; instead, hardness was governed primarily by indentation load and local response of the rock salt carbide
matrix.
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All authors Ali Sarikhani, Ana C. Feltrin, Gregory E. Hilmas, David W. Lipke, Douglas E. Wolfe, Stefano Curtarolo, Shen J. Dillon, William G. Fahrenholtz
Materials Science
Beyond binary at submicron dimensions: crossed-ellipse MTJ free layers as multi-state cells for spintronic crossbars
Arup Ghosh, Ariel Zaig, Colin Ducarme et al. (+3 more)
Spintronic crossbars are promising hardware platforms for energy-efficient neuromorphic computing, but conventional
magnetic tunnel junctions (MTJs) are binary, limiting the information density and synaptic precision of each crosspoint. Here, MuMax3 micromagnetic simulations are used to investigate how size and aspect ratio control the switching and remanent-state landscape of crossed-ellipse MTJ free layers, with permalloy as the main model system and CoFeB checks for transferability. At fixed 8:1 aspect ratio, shrinking the device from 16 micron x 2 micron to 80 nm x 10 nm lowers the absolute switching current but raises the switching field from about 11 Oe to about 301 Oe and increases the SOT current density. At fixed major axis 1.6 micron, aspect-ratio tuning produces a low-field four-state regime, while lower aspect ratios stabilize additional remanent states with lower switching fields and current densities. A 1.6 micron x 0.8 micron device exhibits twelve accessible remanent plateaus in its angle-resolved planar Hall response, with the resolved state count depending on both aspect ratio and absolute size. Projected MTJ readout gives multiple electrical levels, while minimum-energy-path calculations show that the twelve configurations are not all thermally independent. Independent MuMax+ calculations reproduce the multistate
topology and reveal lower-barrier multistep escape pathways between nominally distant states. These results define a geometry-dependent design window for scalable multistate spintronic crossbar
cells.
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All authors Arup Ghosh, Ariel Zaig, Colin Ducarme, Thomas Coppée, Flavio Abreu Araujo, Lior Klein
Materials Science
Lukas Cvitkovich, Klaus Zollner and Jaroslav Fabian
Active control of
magnetic damping is a crucial capability for the development of low-power, tunable spintronic devices. In this work, we demonstrate that the intrinsic
magnetic damping of 2D materials is highly sensitive to the position of the Fermi level relative to
spin-orbit driven anti-crossings, or “
spin hot spots.” Starting from a minimal multi-band model evaluated via Kamberský's breathing Fermi surface theory, we elucidate the fundamental role that energy gaps and band
alignment play in governing
magnetic dissipation. We then translate these theoretical insights to van der Waals
heterostructures, proposing a concrete mechanism for strongly tunable
magnetic damping via electrostatic gating. This concept is validated from first principles via density functional theory calculations on a realistic Fe$_3$GeTe$_2$/
graphene heterostructure. Our calculations reveal that an out-of-plane electric field selectively shifts the relevant energy bands, enabling the modulation of the
heterostructure's
magnetic damping over several orders of magnitude. These findings establish a robust theoretical framework and a promising materials platform for electrically tunable magnetization dynamics.
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Materials Science
Effect of Near-surface Thermal Spikes on Radiation Hardness of Gallium Oxide
Tomás Fernández Bouvier, Umutcan Bektas, Alexander Azarov et al. (+10 more)
Gallium oxide (Ga$_{2}$O$_{3}$) stands out as an extraordinary high radiation-tolerant
semiconductor, because its
lattice displacements induce polymorph transitions, holding material crystalline instead of leading to amorphization. Meanwhile, under extremely severe irradiation conditions many
crystals become amorphous, often starting from surfaces where the translation
symmetry breaks. Here, we show that the surface amorphization may prevail over the crystallisation in Ga$_{2}$O$_{3}$, however only if the mass and energy of irradiated ions produce sufficiently dense heat spikes in the immediate vicinity of the free surface. Applying machine-learned molecular dynamics simulations together with experimental broad-beam and focused ion-beam irradiations, we conclude that the presence of the free surface enables asymmetric displacements of Ga and O atoms, leading to a local non-stoichiometry. Consequently, when the affected cascade volume is sufficiently large, this compositional imbalance suppresses recrystallization and promotes amorphization. As such, our results are ready to use for tailoring irradiation conditions to either prevent or induce surface amorphization, depending on the requirements of the intended applications in Ga$_{2}$O$_{3}$ or other compound
semiconductors.
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All authors Tomás Fernández Bouvier, Umutcan Bektas, Alexander Azarov, Ru He, Nico Klingner, René Hübner, Paul Chekhonin, Aleksi Leino, Kai Nordlund, Javier García Fernández, Andrej Kuznetsov, Gregor Hlawacek, Flyura Djurabekova
Materials Science
From bending to stretching driven peeling of heterogeneous adhesives
Laurent Ponson
We study theoretically the peeling behavior of adhesives. Adopting a fracture mechanics approach, we derive the equation of motion of the adhesion front propagating at the interface between the adhesive and the substrate from which the peel strength is inferred. The originality of our approach lies in the description of the interplay during peeling between the stretching and the bending modes of deformation of the adhesive that is described as a F{\”o}ppl-Von Karman's thin film. Considering first a straight adhesion front, we retrieve the most salient feature of homogeneous adhesives, namely a peeling angle dependent peel strength driven by bending at large angles and by stretching at low angles. We also derive the shape of the adhesive that can be described using a single bending length scale derived from our model. We then investigate the impact of adhesion heterogeneities. We evidence that the deformations of the adhesion front are governed by a non-local interface elasticity the strength of which decreases with the peeling angle. This phenomenon reflects the transition between a stretching dominated peeling at low angle to a bending driven peeling at large angles that is captured in our model. This transition impacts the stability of adhesive fronts that relaxe more slowly from perturbations and gives rise to a stronger toughening effect in presence of a disorder distribution of adhesion energy at low peeling angles. Overall, this study sheds light on the central role played the elastic deformations of adhesives on their peeling behavior. The proposed framework unfolds the complex interplay between the deformation of adhesives and the peeling driving force that may be leveraged to engineer heterogeneous adhesives with enhanced properties. It also provides rich insights on the mechanisms underlying the emergence of non-local elasticity in interface problems.
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Materials Science
Optical properties of single-crystal As2Se3 from first principles
Juan J. Meléndez
Crystalline As2Se3 is a promising layered chalcogenide for mid-infrared photonics and optoelectronic applications, yet its fundamental electronic and optical properties remain debated. This paper combines density functional theory with G0W0 quasiparticle corrections and Bethe-Salpeter equation (BSE) calculations to deliver a robust description of its band structure and optical response. The G0W0 results reveal an indirect band gap of 2.31 eV with nearly degenerate direct transitions at Gamma, while the BSE spectra exhibit strong polarization-dependent anisotropy and pronounced excitonic effects. Several bound
excitons are identified near the absorption onset, clarifying the role of electron-hole interactions and resolving previous controversies regarding the nature of the optical gap and the contribution of lone-pair states. This work provides a unified and quantitatively accurate picture of As2Se3, reinforcing its potential for next-generation infrared and anisotropic photonic devices.
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Materials Science
Benchmarking Machine-Learning Interatomic Potentials for Dynamical Stability in Inorganic Semiconductor Nanocrystals: A CdSe Case Study
M. Usman, M. Suleymanova, Z. U. Abideen et al. (+2 more)
Machine-learning interatomic potentials (MLIPs) enable nanosecond-scale atomistic simulations of inorganic
semiconductor nanocrystals, but low errors on held-out configurations do not necessarily guarantee stable molecular dynamics. We
benchmark five graph-neural-network MLIPs, SchNet, PaiNN, NequIP, Allegro and MACE, for dynamical stability in a chloride-passivated cadmium selenide nanocluster containing 149 atoms. The models were trained under harmonized conditions on 1,000 configurations and evaluated against 2,000 held-out configurations generated using density functional theory, considering force accuracy, computational efficiency, uncertainty and structural stability during 1 ns simulations at 300 K. Allegro produced the lowest validation force mean absolute errors, ranging from 12 to 14 meV per angstrom, whereas SchNet produced the largest, ranging from 84 to 110 meV per angstrom. This ranking did not predict dynamical robustness: NequIP remained stable for 1 ns without additional training data, whereas MACE became stable only after an ensemble-based active-learning procedure added 34 uncertainty-selected configurations. PaiNN and Allegro remained unstable after the addition of 100 and 95 configurations, respectively, and SchNet also failed to achieve stable dynamics within the tested augmentation budget. Under the
benchmark hardware conditions, the machine-learning potentials required 6-66 ms per molecular-dynamics step, compared with approximately 20 s for density functional theory. These results show that held-out prediction errors alone are insufficient for selecting interatomic potentials for finite, surface-dominated nanostructures. Reliable deployment requires long-timescale dynamical testing combined with uncertainty-guided refinement, while the effectiveness and data efficiency of active learning remain strongly architecture dependent.
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All authors M. Usman, M. Suleymanova, Z. U. Abideen, M. Fernández-Pendás, I. Infante
Materials Science · Cross-listed from cond-mat.str-el
Twinning of domains and spin anisotropy in K$_5$Fe$_4$Ag$_6$Te$_{10}$
Jiayu Guo, Hengyang Zhong, Dongsheng Yuan et al. (+12 more)
The Fe-based
superconductors are derived from metallic parent compounds with nematic and stripe
magnetic orders, which lead to two types of
magnetic domains. Recently it was found that K$_5$Fe$_4$Ag$_6$Te$_{10}$ (KFAT), an Fe-based
semiconductor, exhibits similar nematic and stripe
magnetic orders, and is thus an analogue to the Fe-based
superconductors in the limit of localized electrons. In this work, the superstructure and
magnetic domains of KFAT are elucidated by fully mapping the reciprocal space using time-of-flight single
crystal neutron diffraction. In KFAT, Fe and Ag atoms order to form a $\sqrt{5}\times\sqrt{5}$ superstructure containing $2\times2$ Fe blocks, which leads to two superstructure domains with identical main Bragg peaks but distinct superstructure peaks. Below $T_{\rm N}\approx35$~K,
magnetic and nematic orders break in-plane rotational
symmetry of the tetragonal $\sqrt{5}\times\sqrt{5}$ superstructure, and further give rise to two
magnetic domains. These four equally populated domains account for the complex scattering pattern observed in our time-of-flight elastic
neutron scattering measurements. Using polarized
neutron scattering, we demonstrate a prominent
spin anisotropy with an easy-plane spanned by the $c$-axis and the intra-block antiferromagnetic Fe-Fe bond direction. Such an anisotropy at ${\bf q}\neq0$ persists well above $T_{\rm N}$, accounts for the in-plane ${\bf q}=0$
magnetic anisotropy observed in uniaxial-strained KFAT, and offers an indicator for discovering similar piezomagnetic effects in other materials.
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All authors Jiayu Guo, Hengyang Zhong, Dongsheng Yuan, Xuejuan Gui, Youzhe Chen, Nathan Giles-Donovan, Naomi Kawamura, Masaaki Matsuda, Yaohua Liu, Feng Ye, Rongyan Chen, Robert J. Birgeneau, Xingye Lu, Jincheng Wang, Yu Song