Materials Science · Cross-listed from physics.comp-ph
Second-Order Homogenization of Particulate Elastomeric Composites for Structural-Scale Damage Analysis
Krishna Murthy Pabbu, Tarkes Dora Pallicity and Nelson Muthu
Damage prediction in particulate elastomeric composites is challenging due to the strong material heterogeneity, nearly incompressible behavior of the
matrix, and the presence of localized stress concentrations arising from
matrix-inclusion interactions. In the present work, a computational framework is developed for damage propagation analysis of particulate elastomeric composite structures. The effective constitutive response of the heterogeneous material is first determined using the second-order homogenization method. The resulting homogenized response is subsequently used to identify equivalent hyperelastic material parameters for structural simulations. A three-parameter isotropic damage model is incorporated to capture damage-induced softening. A mixed displacement-pressure finite element formulation, is used to alleviate volumetric locking associated with nearly incompressible property of elastomers. The proposed framework is validated through full-scale simulations and homogenized response involving composites with varying inclusion volume fractions. Numerical investigations demonstrate that the homogenized models is able to reproduce the global force-displacement response within 2% error and damage
evolution characteristics of the heterogeneous composites while significantly reducing the computational cost.
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Materials Science · Cross-listed from cond-mat.mes-hall
Magnon chiral damping beyond the Dzyaloshinskii-Moriya interaction
Darpa Narayan Basu, Subhadip Ghosh, Peter M. Oppeneer et al. (+2 more)
Magnon chiral damping denotes damping that is asymmetric with respect to the
magnon wave vector. Such nonreciprocity has been attributed to antisymmetric Dzyaloshinskii-Moriya
spin interactions. Here, we provide an alternative theoretical explanation of
magnon chiral damping using linear
spin-wave theory and antisymmetric Gilbert damping introduced within the Landau-Lifshitz-Gilbert equation of motion. First, employing a minimal model of a single sublattice ferromagnet on a rectangular
lattice, we show that the effective
magnon damping is independent of the system's energy, including contributions from Dzyaloshinskii-Moriya interactions. Considering scalar nonlocal Gilbert damping, the effective damping parameter $\alpha_{\rm eff}$ becomes wave-vector dependent. In the long-wavelength limit, $\alpha_{\rm eff}$ acquires a quadratic dependence on $\bf{k}$. Furthermore, the antisymmetric component of the Gilbert damping tensor gives rise to asymmetric (nonreciprocal)
magnon damping. We find the asymmetry to be linear in $\bf{k}$ in the long-wavelength limit, consistent with recent experiments. Extending the analysis to a two-sublattice system, we consider cross-sublattice Gilbert damping. In the presence of only scalar Gilbert damping, broken reciprocity in
magnon relaxation arises from Dzyaloshinskii-Moriya interactions. In contrast, the cross-sublattice antisymmetric component of the Gilbert damping tensor can generate nonreciprocal
magnon damping even if the Dzyaloshinskii-Moriya interaction is parametrically set to zero, providing an alternative mechanism for asymmetric
spin-wave relaxation. Notably, the nonreciprocity induced by antisymmetric Gilbert damping is roughly an order of magnitude larger than that arising from Dzyaloshinskii-Moriya interactions.
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All authors Darpa Narayan Basu, Subhadip Ghosh, Peter M. Oppeneer, Alexander Mook, Ritwik Mondal
Materials Science · Cross-listed from cond-mat.str-el
Quantum metric induced nonlinear transport in the hidden loop-current phase of kagome metal RbV$_3$Sb$_5$
Jia-Chen Shi, Shupeng Xu, Utkarsh Khandelwal et al. (+4 more)
A hidden low-temperature phase with possible loop-current order has been proposed in the kagome metals AV$_3$Sb$_5$ (A=K, Rb or Cs), but its experimental signatures remain subtle and indirect. Here, we use third-order nonlinear transport to probe this hidden phase in RbV$_3$Sb$_5$. At ~35 K, the longitudinal cubic response develops a strong kink and pronounced directional anisotropy with a strong departure from common relaxation time scaling, while the transverse cubic response acquires a
magnetic field-odd component at the same temperature. Their coincident onset identifies the third-harmonic response as a sensitive marker of the low-temperature electronic reconstruction with time-reversal broken
symmetry. Crucially, we find that the
quantum metric quadrupole contributes directly to the longitudinal third-order response. In a loop-current charge-density-wave model, its direction selective enhancement captures the observed angular reconstruction. Our work shows how higher-order nonlinear transport translates subtle changes in electronic
symmetry and
quantum metric into measurable electrical signatures in
quantum materials that is important for studying complex electronic phases of matter.
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All authors Jia-Chen Shi, Shupeng Xu, Utkarsh Khandelwal, Nashra Pistawala, Luminita Harnagea, Steven J. May, Ritesh Agarwal
Materials Science
Directional strain control of magnetism in MnBi$_2$Se$_4$, MnSb$_2$Se$_4$, and MnSb$_2$Te$_4$ freestanding monolayers
Swarnava Ghosh, Tanvir Sohail and Markus Eisenbach
MnBi$_2$Se$_4$, MnSb$_2$Se$_4$, and MnSb$_2$Te$4$ are layered
magnetic quantum materials of interest for spintronic and topological electronic applications, where control of
magnetic order at the atomic scale is essential. These materials are particularly sensitive to strain. We investigate their strain-dependent magnetism in the monolayer limit using first-principles calculations across the full two-dimensional strain space spanned by independent variations of the two in-plane strain components. Our results show that the Mn-projected local moments depend primarily on the volumetric strain, whereas the
magnetic ground state, exchange interactions, magnetocrystalline anisotropy, and ordering temperature show pronounced directional and composition-dependent responses. We also observe strain-induced competition between the phases, with MnBi$_2$Se$_4$, and MnSb$_2$Se$_4$ monolayers exhibiting a more diverse range of competing
magnetic states, while MnSb$_2$Te$_4$ monolayer remains ferromagnetic over a larger portion of strain space. MnSb$_2$Te$_4$ also exhibits a substantially larger out-of-plane magnetocrystalline anisotropy, while showing a weaker dependence on strain than the Se-based materials. The calculated
magnetic ordering temperature maps further highlight the role of two-dimensional strain to tune thermal
magnetic stability in these materials. These results establish magnetoelastic trends across this family of Mn-based chalcogenide monolayers.
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Materials Science
Fundamental concepts of thermal phonon coherence
Theodore Maranets, Haoran Cui, Milad Nasiri et al. (+2 more)
As scientists seek to transcend traditional material property relationships, novel structures with artificial periodicity, configurational complexity, and disorder are increasingly being explored. For
phonons, these architectures can induce significant phase correlations, which strongly shifts
lattice heat conduction away from the conventional framework of particle-like scattering. This thermal
phonon coherence can develop in space and time separately, resulting in distinct wave-like phenomena. Here we rigorously outline the theories of
phonon spatial and temporal coherence. Crucially, this review focuses on demystifying and building conceptual understanding of the fundamental principles linking the various thermal conductivity and
phonon property results reported in the literature. Furthermore, we use this understanding to establish a comprehensive physical picture of the wave nature of thermal
phonons, unifying the spatial and temporal coherence theories. Altogether, the theoretical dissections in this review provide an extensive knowledge base for understanding and engineering thermal
phonons in complex materials.
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All authors Theodore Maranets, Haoran Cui, Milad Nasiri, Evan Doe, Yan Wang
Materials Science · Cross-listed from cond-mat.mes-hall
Unveiling Three-Dimensional Skyrmion Transitions Through Vortices and Monopoles
Melissa E. Henderson, Daichi Kurebayashi, Benjamin Heacock et al. (+9 more)
Magnetic skyrmions represent
vortex-like
spin configurations that provide a robust platform for next-generation spintronic technologies. Although they are often treated as two-dimensional objects with integer topological charge, their extension into three-dimensional strings realizes other composite structures with unique device functionalities that transcend planar frameworks. Unfortunately, a lack of bulk probes has failed to realize such higher-dimensional topological structures and their implementations. Here, we report the first experimental visualization of three-dimensional topological $Q = 0$ skyrmion structures using
neutron scattering
tomography techniques across the
equilibrium phase of a Co$_8$Zn$_8$Mn$_4$ sample. Disordered skyrmion states reveal metastable skyrmioniums and composite topological objects novel to bulk systems.
Vortex-antivortex
lattices mediate changes in
topology, with unprecedented transition pathways via a coupling of merons and monopoles. The present realization of bulk Q = 0 quasiparticles and meron-mediated dynamics paves the way for higher-dimensional spintronic frameworks through multi-bit encoding architectures, unidirectional transport schemes, and monopole-mediated controls.
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All authors Melissa E. Henderson, Daichi Kurebayashi, Benjamin Heacock, Wangchun Chen, Charles W. Clark, David G. Cory, Dusan Sarenac, Shannon Watson, Jonathan S. White, Lisa DeBeer-Schmitt, Oleg A. Tretiakov, Dmitry A. Pushin
Materials Science
Fracture of Lattice Materials from Low to High Relative Density
Adam P. Taylor, Sage Fulco and Kevin T. Turner
Lattice materials have highly tunable mechanical properties that are controlled by their internal geometry and base material behavior. While fracture models for low-density
lattices are well-established, the fracture of
lattices at relative densities above 30% remains largely unexplored. Here, we present an analytical model that combines homogenization methods and blunt-crack fracture theory to predict the fracture toughness of triangular and hexagonal
lattices over a wide range of relative densities. Finite element modeling corroborates the analytical framework and demonstrates a shift in failure mechanisms between low and high relative density regimes. At high relative densities, failure is dominated by nodal stress concentrations, which are strongly influenced by the local crack-tip geometry and the macroscopic crack path. Significant stress redistribution is observed as the relative orientation and
lattice fillet radius are varied, resulting in increased fracture toughness relative to baseline geometries. Furthermore, quasi-brittle poly(methyl methacrylate) (PMMA)
lattices achieve about a 1.6x enhancement in fracture toughness relative to perfectly brittle
lattices as failure is delayed by localized plasticity. Notably, some quasi-brittle
lattices are found to exceed the fracture toughness of their base material – a feature only possible when the
cell size is large compared to the base material's plastic radius. Experiments on
lattice fracture specimens made from
laser-cut PMMA validate the finite element results, but highlight the
stochastic nature of failure in brittle
lattice materials, especially at higher relative densities.
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Materials Science
Facet- and thickness-dependent band-edge alignment at ZrSe\texorpdfstring{$_3$}{3} surfaces: hybrid-functional calculations with spin-orbit coupling
Sandro G Holanda, Bruno Ipaves, Astrid Campos-Mata et al. (+4 more)
Transition-metal trichalcogenides MX$_3$ are quasi-one-dimensional van der Waals materials whose layers form through lateral chain binding, giving them an interlayer cleavage plane and in-plane electronic anisotropy. Among them, ZrSe$_3$ is stable under ambient conditions and semiconducting. Exfoliated
crystals expose four crystallographic planes, and electrocatalytic measurements on an individual
crystal assigned the hydrogen
evolution activity to the high-energy (210) facet rather than to the basal plane. Those non-basal surfaces remain uncharacterized, since the available calculations treat either the bulk
crystal or the free-standing basal monolayer. Here, we compute the surface energies and the
equilibrium morphology of these four surfaces with a dispersion-corrected semilocal functional, and their band-edge
alignment with the HSE06 hybrid functional including
spin-orbit coupling. The surface energies span nearly an order of magnitude, from \SI{0.097}{\joule\per\meter\squared} for (001) to \SI{0.869}{\joule\per\meter\squared} for (010), and the Wulff shape exposes the four observed planes with area fractions of \SI{17.1}{\percent}, \SI{4.4}{\percent}, \SI{71.4}{\percent}, and \SI{7.0}{\percent}. The ionization potential varies by \SI{0.45}{\electronvolt} between facets and the electron affinity by \SI{0.80}{\electronvolt}, the gap of (210) falls from 1.43 to \SI{0.94}{\electronvolt} between 10 and \SI{23}{\angstrom}, and (010) remains metallic. The facets separate according to whether the cut preserves or distorts the Se-Se dimer, and the distorted dimers concentrate the frontier states. Because the same dimer governs the bulk electronic structure of the MX$_3$ family, the criterion transfers to the related trichalcogenides.
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All authors Sandro G Holanda, Bruno Ipaves, Astrid Campos-Mata, Shreyasi Chattopadhyay, Pulickel M Ajayan, Douglas S Galvao, Marcelo L Pereira Junior
Materials Science
Altermagnetism produces pair emission and absorption from dark excitons and magnons in La$_2$O$_3$Mn$_2$Se$_2$
Birender Singh, Xian Xu, Sabrina R. Hatt et al. (+21 more)
Altermagnets' (AMs) non-relativistic
spin splitting enables novel states, spintronic and magneto-optical devices, though their optical signatures remain elusive. Here, we report
exciton-
magnon emission and absorption: optical sidebands from a
spin-forbidden dark
exciton, a direct consequence of altermagnetic
symmetry. Combined optical spectroscopy and first-principles calculations reveal that La$_2$O$_3$Mn$_2$Se$_2$ is an altermagnetic
insulator, hosting a strongly bound,
spin-forbidden dark
exciton and a higher-energy bright
exciton. Photoluminescence (PL) and absorption reveal mirror-image sidebands, Stokes-shifted in emission and anti-Stokes-shifted in absorption, symmetric about the dark
exciton, whose energy shifts and spectral shapes match the
magnon energy scale and density of states measured independently by inelastic
neutron scattering. The PL intensity tracks the full equal-time
spin-
spin correlator, combining static and dynamical contributions, and rules out alternative processes. This directly couples PL to magnetism, with potential for magneto-optical devices. These results establish
exciton-
magnon spectroscopy as a new route for optically identifying and exploiting AMs.
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All authors Birender Singh, Xian Xu, Sabrina R. Hatt, Suvodeep Paul, Yu-Mi Wu, Chao-Chun Wei, Violet Williams, Kyung-Mo Kim, Yihao Zhang, Mohamed Shehabeldin, Cameron Grant, April Li, Michael Geiwitz, Xiaoyin Li, Garrett E. Granroth, Feng Liu, Qiong Ma, Benedetta Flebus, Judy J. Cha, Vinod M. Menon, Benjamin A. Frandsen, Diana Y. Qiu, Huiwen Ji, Kenneth S. Burch
Materials Science
Far-field terahertz spectroscopy across the charge-density-wave transition in 2H-NbSe$_2$
Dmitriy Yavorskiy, Adil Rehman, Wojciech Brzezicki et al. (+7 more)
Charge-density-wave (CDW) formation in 2H-NbSe$_2$ modifies the low-energy electronic structure and gives rise to collective excitations coupled to the
lattice. Here, we investigate bulk 2H-NbSe$_2$ single
crystals using far-field terahertz time-domain spectroscopy (THz-TDS) in reflection geometry across the CDW transition at $T_{\mathrm{CDW}} \approx 33$~K. Below $T_{\mathrm{CDW}}$, the THz response shows a pronounced high-frequency feature near 1.5~THz together with longer-lived sub-THz oscillations. Both responses progressively weaken upon warming and are strongly suppressed across the CDW transition, supporting their association with the CDW state. Using time-dependent Ginzburg–Landau simulations, we reproduce the main features of the experimental THz response, associating the high-frequency response mainly with CDW amplitude dynamics and the sub-THz response with defect-pinned phase dynamics. The $\sim1.5$~THz feature lies close to the frequency range reported for the Raman CDW amplitude mode, while coupling to
lattice degrees of freedom may also influence its spectral position. We also performed complementary angle-resolved photoemission spectroscopy measurements, which reveal momentum-selective redistribution of near-Fermi-level spectral weight across the transition. Together, these results show that far-field THz spectroscopy provides a sensitive probe of collective CDW dynamics in bulk 2H-NbSe$_2$.
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All authors Dmitriy Yavorskiy, Adil Rehman, Wojciech Brzezicki, Jan Skolimowski, Marcin Białek, Wojciech Knap, Dawid Wutke, Natalia Olszowska, Andrzej Wiśniewski, Ashutosh S. Wadge
Materials Science
Accelerating phase-field simulations on exascale computing systems for faster-than-real-time precipitate aging predictions
Stephen DeWitt, David J. Gardner, Philip Fackler et al. (+4 more)
Three-dimensional phase-field simulations are a gold-standard for microstructure prediction for materials, but their computational cost often limits application-relevant calculations to modest domain sizes and timescales. Here, we present a holistic approach for accelerating
Fourier pseudospectral phase-field simulations by combining performance-portable GPU computing, large-scale distributed-
memory parallelism, and high-order implicit-explicit time integration within the MEUMAPPS C++ framework. We demonstrate this approach with a 1.5-billion-grid-point simulation of the growth and coarsening of 1,920 gamma” precipitates in a Ni-Nb-Fe
alloy. The simulated seven-hour heat treatment is completed in 5.5 hours, making the calculation faster than real time and an estimated 217-501x faster than a CPU-only, first-order baseline. This performance makes three-dimensional simulations of thousands of interacting precipitates tractable, enabling quantitative studies ocollective microstructural phenomena, large simulation ensembles, and real-time integration into controlling and interpreting experiments. Benchmarking shows single-node GPU speedups of up to 17.5x relative to comparable CPU resources, near-ideal strong scaling to 4096 GPUs for a 12-billion-grid-point problem, and a further 2.6-2.9x acceleration from fourth-order time integration at scientifically relevant error tolerances. These results establish a performance-portable strategy for exploiting leadership-scale GPU systems that is applicable to a broad class of
Fourier pseudospectral simulations beyond phase-field models such as fluid dynamics and
crystal plasticity simulations.
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All authors Stephen DeWitt, David J. Gardner, Philip Fackler, Yonggil Song, Miroslav Stoyanov, Carol S. Woodward, Balasubramaniam Radhakrishnan
Materials Science
Measuring trainable degrees of freedom in materials graph neural networks: a random-subspace intrinsic dimension analysis
Shehroz Ahmad Shoaib and Kangming Li
Final predictive accuracy is the standard basis for comparing graph neural networks (GNNs) in materials-property prediction, but it does not show how strongly performance depends on access to trainable parameter-space directions. Here, we introduce trainable-degree dependence as a complementary characterization of materials GNN learning. Using random-subspace intrinsic-dimension analysis, we train CGCNN, ALIGNN, and DimeNet++ in randomly oriented parameter subspaces across six prediction tasks and measure how performance recovers as independent trainable degrees of freedom are restored. The resulting recovery curves separate endpoint accuracy from the trainable-dimensional demand required to recover it. They reveal distinctions that final errors alone miss: metallic classification and log-bulk-modulus regression recover near-reference performance from small fractional subspaces, formation-energy and band-gap prediction show stronger architecture dependence, and
phonon prediction is most sensitive to dimensional restriction.
Dataset-size sweeps show that band-gap models require larger fractional subspaces as training data grows, whereas formation-energy and bulk-modulus responses are more stable. A width sweep shows that fractional thresholds can remain stable while absolute threshold dimensions increase with model size. Random-subspace analysis therefore provides a targeted stress test for how materials GNNs use their optimization space.
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Materials Science
Linking Topological Medium Range Order and Density-Wave Coherence to Metallic Glass Ductility
Minhazul Islam, Muchen Wang, Andrea Fantin et al. (+10 more)
Metallic glasses exhibit pronounced composition-dependent mechanical properties, yet identifying the structural origins of these changes remains difficult. An outstanding issue is how to correlate different forms of medium range order (MRO), defined at different length scales and accessed through different experimental observables, and to understand their connection to properties. We combine synchrotron reduced density function, G(r), with machine-learning-assisted four dimensional scanning transmission electron microscopy (4D-STEM) to examine
geometric and topological MRO in five Zr-based metallic glasses. Density wave analysis of G(r) provides a
geometric MRO descriptor through the coherence length of atomic density correlations, while 4D-STEM reveals nanoscale topological and chemical MRO motifs, including
crystal-like local ordering with distinct rotational
symmetries. We show that the G(r)-derived coherence length captures an important baseline tendency for cooperative ductile relaxation, while composition-dependent topological MRO provides an additional structural contribution that helps explain the observed mechanical responses. In particular, increasing Zr content suppresses Cu-rich FCC-like MRO, increases the cooperative coherence volume, and promotes fine Zr-rich HCP-like local order associated with enhanced ductility. These results identify the combined structural influence of
geometric and topological MRO as a key basis for composition-dependent mechanical response in metallic glasses.
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All authors Minhazul Islam, Muchen Wang, Andrea Fantin, Geun Hee Yoo, Ji Young Kim, Hamdan Ashfaq, Eun Soo Park, Robert Maass, Yunzhi Wang, Yue Fan, Hee-Suk Chung, Sang-Chul Lee, Jinwoo Hwang
Materials Science · Cross-listed from cond-mat.str-el
Spectroscopy of phonon-coupled integer and fractional Chern insulators: emergence of polarons and chirality deficit of graviton mode
Min Long, Yuzhu Wang and Zi Yang Meng
Strong electron-
phonon coupling can destabilize both Chern
insulators (CIs) and fractional Chern
insulators (FCIs) in favor of charge order, but whether the instabilities in CI and FCI share a common microscopic mechanism remains unclear. In this paper, we address this question by studying a flat-band Haldane model coupled to dynamical Holstein
phonons at integer and fractional fillings using density-
matrix renormalization group with local basis optimization. We find that the low-energy effects of
phonons are dominated by their dressing of charge-neutral collective modes. In the CI and FCI,
phonons dress
excitons and magnetorotons into composite modes that we identify as
exciton polarons and magnetoroton polarons, respectively. These modes soften strongly upon approaching the transition, while the momenta of their energy minima anticipate the ordering wave vectors of the charge-ordered phases. The
phonon spectrum, in turn, acquires dispersive features inherited from the
exciton and magnetoroton modes, providing direct
lattice signatures of these neutral excitations. Within the FCI phase, electron-
phonon coupling also enhances the opposite-chirality spectral weight of the graviton response, thereby resulting in a chirality deficit. Our results provide a unified excitation-based picture of
phonon-driven instabilities in CIs and FCIs and establish
lattice dynamics as a probe of their neutral collective modes.
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Materials Science · Cross-listed from astro-ph.GA
Photoelectron and electron microscopy investigation of laboratory grown Mg-silicate space dust analogues
Steffen Friis Holleufer, Mie Andersen, Frederik Granzow Doktor et al. (+9 more)
The atomic structure at the surface of interstellar silicate dust particles likely plays a key role in a variety of chemical processes occurring in
star- and
planet-forming regions of the interstellar medium (ISM). Here, we use the photoelectric effect to characterize, in situ, the local chemical structure of Mg-silicate nanoparticulate films, and ex situ electron microscopy to trace changes to morphology resulting from different starting compositions. Nanoparticulate films are prepared via co-deposition of Si, Mg and O atoms on a graphitic substrate under ultra-high
vacuum (UHV) and are characterised with X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure measurements. Analysis, supported by density functional theory calculations, shows that adjusting the Mg-to-Si ratio from 3.5 to 1.8 changes particle composition from a mixture of MgO and Mg-silicate towards predominantly Mg-silicate. Annealing in UHV also pushes the composition towards Mg-silicate, however, non-stoichiometric chemical motifs are always observed, presenting a distribution of potentially catalytically active sites. Electron microscopy images show composition-dependent film morphologies that restructure differently upon thermal annealing. The Mg-silicate nanoparticulate films presented here are characterised as a 2D version of ISM analogue dust particles prepared via
laser ablation and are therefore a more readily suitable model for surface science investigations into the catalytic properties of interstellar Mg-silicate dust.
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All authors Steffen Friis Holleufer, Mie Andersen, Frederik Granzow Doktor, Lars Eric Borchert, Martin Wibrand Larsen, Duncan S. Sutherland, Zheshen Li, Alexei Preobrajenski, Jeppe Vang Lauritsen, Cornelia Jäger, Liv Hornekær, Andrew Cassidy
Materials Science
Catalogue of Collinear Magnetic Structures in Stoichiometric Materials
Liangliang Huang, Houhao Wang, Yuanze Song et al. (+3 more)
Magnetic materials persistently serve as a fertile platform for exploring novel
quantum emergent phenom ena and advancing information technologies. Reliably determining their
magnetic structures (MSs), which is essential for understanding their emergent
quantum properties, usually depends on experiments such as
neutron scattering. Here, noting that around half of the MSs in MAGNDATA (a database of experimentally determined MSs) are collinear, we adopt the
spin space groups (SSGs) to preset the candidate MSs for a given nonmagnetic
crystal structure to be collinear from the outset. On the other hand, more than 80% of the collinear magnets in MAGNDATA are subject to maximal subgroups of nonmagnetic groups which are collinear SSGs, and we then enumerate all collinear MSs formed at Wyckoff positions by the maximal collinear SSG subgroups of the 230 nonmagnetic space groups. With such exhaustive enumeration, we categorize all
symmetry-allowed collinear MSs for the 72,075 nonmagnetic stoichiometric structures in Inorganic
Crystal Structure Database, obtaining 365,639 collinear MSs. We then determine the ground-state SSG
symmetries of 7,824 collinear magnets among the 21,315 selected materials using first-principles calculations. These magnets then undergo a comprehensive topological classification combining SSGs and
magnetic space groups, outputting thousands of new
magnetic topological materials. The experimentally determined MSs in MAGNDATA represent the tip of the iceberg in our computational database of collinear magnets, expected to guide MS characterization by experimentalists and further investigation towards spintronics applications.
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All authors Liangliang Huang, Houhao Wang, Yuanze Song, Ruixi Pu, Xiangang Wan, Feng Tang
Materials Science
A Si-on-SiC Platform for Interfacing with Vanadium Dopants in the Telecom O-Band
Timothy Draher, Nolan Bitner, Vasileios Niaouris et al. (+6 more)
Vanadium color centers in silicon carbide (SiC) offer telecom O-band emission, sub-microsecond optical lifetimes, and second-scale
spin relaxation times, rendering them promising candidates for
quantum network nodes. However, efficient
photon extraction from the high-refractive-index SiC host remains challenging. Here, we introduce a silicon-on-SiC heterogeneous photonic platform in which silicon nanocavities evanescently couple to shallow vanadium dopants in commercial 4H-SiC, enabling efficient zero-
phonon line (ZPL) collection under resonant excitation. In as-grown ensembles, we observe Purcell-enhanced photoluminescence with transient spectral hole burning linewidths of 50 MHz on microsecond timescales. In dilute implanted samples, we isolate individual vanadium centers with high-purity single
photon emission and a Purcell-enhanced lifetime of 109 ns. The entire optical interface operates through a single lensed fiber, including a 905 nm repump
laser that recovers the vanadium charge state with 95% efficiency. These results establish Si-on-SiC as a scalable, foundry-compatible platform for telecom-wavelength
spin-
photon interfaces.
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All authors Timothy Draher, Nolan Bitner, Vasileios Niaouris, Claire E. McDermott, David Czaplewski, Supratik Guha, David D. Awschalom, F. Joseph Heremans, Alan M. Dibos
Materials Science
Pyroelectric thermo-wave probing of BaZr0.2Ti0.8O3 ceramics
Nicholas V. Morozovsky, Yuriy O. Zagorodniy, Mykola Yelisieiev et al. (+9 more)
BaxZr1-xTiO3 ceramics with 0.15 < x < 0.25, which have high dielectric permittivity, small leakage currents and low dissipation factor, are promising materials for tunable capacitor devices, multilayered ceramic capacitors and piezoelectric actuators. These materials reveal relaxor properties due to the local chemical strains caused by the isovalent substitution of Ti4+ ions by Zr4+ ions with a larger ionic size. However, to the best of our knowledge, the pyroelectric properties of BaxZr1-xTiO3 ceramics with x~0.2 have not been studied. To fill the gap in knowledge, we perform the pyroelectric thermo-wave probing of BaZr0.2Ti0.8O3 ceramics prepared by the solid-state synthesis. Results of the thermo-wave probing of the most interesting polar states, namely polarized, depolarized, relaxed and restored polarized states, reveal the pronounced pyroelectric response that can be strongly asymmetric with respect to the opposite surfaces of the ceramics. The asymmetry and profiles of pyroelectric response depend significantly on the pre-history of the electric field cycling indicating possible non-ergodic relaxor-type polar states in the ceramic sample. X-ray diffraction spectrum, recorded at room temperature, reveals the virtual absence of the macroscopic tetragonality and the weak asymmetry of the (200) peak, which indicate the small tetragonality inside the Ti-enriched polar nanoregions. Decrease of the relative intensity of the Raman band at 714 cm-1 occurring upon heating evidences the diffuse ferroelectric-paraelectric phase transition between 30 C and 40 C. The temperature dependence of the dielectric permittivity obeys modified Curie-Weiss law with power 1.4, indicating that both ordered ferroelectric and relaxor states coexist in the BaTi0.8Zr0.2O3 ceramics.Results can be useful for elaboration of lead-free relaxor ferroelectric ceramics for advanced pyroelectric applications.
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All authors Nicholas V. Morozovsky, Yuriy O. Zagorodniy, Mykola Yelisieiev, Oleksandr S. Pylypchuk, Mykola O. Semenenko, Iryna V. Kondakova, Lesya P. Yurchenko, Viktor Bovtun, Valentin V. Laguta, Eugene A. Eliseev, Volodymyr M. Dzhagan, Anna N. Morozovska
Materials Science · Cross-listed from cs.LG
Bounding Retraining Equivalence and the Deletion Floor in Materials Machine Unlearning
Can Polat, Mustafa Kurban, Erchin Serpedin et al. (+1 more)
In materials machine learning, closely related retained structures can sustain accurate property predictions even after removing a specific record, rendering post-deletion prediction error an ambiguous metric for machine unlearning. To resolve this ambiguity, we define the deletion floor as the expected target loss under a specified retraining procedure at the deleted request. Standard indistinguishability constraints yield a sharp interval bounding an update's target loss around this baseline reference. Theoretically, a conditional neighbor bound links a low deletion floor directly to retained fit, prediction regularity, and local label agreement, while an exact ridge identity isolates residual fit from the prediction change induced by record deletion. Empirically, controlled redundancy sweeps show an $\approx 8\times$ drop in median normalized retraining loss when one retained relative remains after deletion. Across two distinct fitting regimes in a paired Materials Project study, the lower-floor regime also exhibits a larger prediction change on more than 50% of the shared requests. Systematic comparisons against approximate updates and the original model decouple deliberate target suppression from preserved overall model utility. Consequently, request-level unlearning evaluations should report reference loss, prediction change, and retained utility together, interpreting post-deletion accuracy against what retraining itself leaves behind.
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All authors Can Polat, Mustafa Kurban, Erchin Serpedin, Hasan Kurban
Materials Science
Density functional perturbation theory of meta-generalized gradient approximations using algorithmic differentiation
Bruno Ploumhans, Niklas Frederik Schmitz and Michael F. Herbst
Density functional perturbation theory (DFPT) is an established framework for the computation of derivatives in plane-wave density functional theory (DFT). We present an implementation of DFPT for exchange-correlation (XC) functionals $E_\mathrm{xc}(\rho,\tau)$ that incorporate an explicit dependence on both the density $\rho$ and the kinetic energy density $\tau$. This covers the popular class of semilocal meta-generalized gradient approximations (meta-GGAs) as well as broader nonlocal parametrizations. We sidestep the derivation of cumbersome XC second energy derivative expressions by recasting these derivatives as a Jacobian-vector product of the XC potentials, which we evaluate with algorithmic differentiation (AD) techniques. Integration with our previously developed AD-DFPT framework [N. F. Schmitz et al., npj Comput. Mater. 12, 6 (2026)] provides access to derivatives of arbitrary ground state quantities with respect to arbitrary perturbations. We employ AD-DFPT to compute a range of response properties for ZnO and BaTiO3, and find that the recent r2SCAN01 meta-GGA functional generally outperforms LDA and PBE. Finally, we showcase the optimization of a neural-network meta-GGA to self-consistently reproduce hybrid-DFT reference densities of bulk silicon, using AD-DFPT gradients. Overall, these results establish AD-DFPT as a versatile route for computing DFT derivatives at the meta-GGA level, be they common response properties or the unusual derivatives required for the gradient-based training of novel XC functionals.
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Materials Science
AI-Assisted Identification of Magnetic Orders and Skyrmions
Haowen Yang, Sophia Huerta and Yingying Wu
Exotic
magnetic orders in two-dimensional (2D) materials are attracting huge interest for energy-efficient spintronic applications, yet realizing robust high-temperature van der Waals antiferromagnets and topological
magnetic states remains challenging. In this work, we develop a machine-learning framework for identifying
magnetic orders and predicting magnetization using structural, compositional, and electronic information derived from the Materials Project. Fixed-length descriptors are constructed for two complementary tasks: ferromagnetic (FM) versus antiferromagnetic (AFM) classification and quantitative magnetization prediction.
Magnetic order is classified using a LightGBM model trained on structure-derived descriptors without explicitly including
magnetic descriptors. Five-fold cross-validation grouped by chemical system is used to reduce chemical leakage, together with hyperparameter and classification-threshold optimization. On an isolated test set, the classifier achieves a balanced accuracy of 93.6% in the testing set. Magnetization is predicted using a residual multilayer perceptron with compositional, structural, electronic, and task-specific initial-state descriptors. A logarithmic target transformation and robust weighted loss are used to account for the broad magnetization distribution, while three independently trained models are combined into a final ensemble. The model achieves a mean absolute error of 0.686 {\mu}B/formula unit. For selected
magnetic candidates, simulated
magnetic imaging and phase-reconstruction analysis are further used to investigate magnetization textures and skyrmion-like features through normalized magnetization profiles and topological charge. This framework provides an efficient approach for screening 2D
magnetic materials and prioritizing candidates for antiferromagnetic and topological spintronic applications.
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Materials Science
Ultra-high vacuum Raman platform for in situ characterization of graphene nanoribbons
Jeong Ha Hwang, Amogh Kinikar, Lukas Rotach et al. (+9 more)
Atomically precise
graphene nanoribbons (GNRs) exhibit tunable electronic and
magnetic properties governed by edge
topology and finite-size effects, which make them versatile platforms for next-generation electronic and spintronic applications. However, the unpaired pi-electrons responsible for their
magnetic properties simultaneously make them highly susceptible to chemical degradation under ambient conditions. This intrinsic reactivity poses a central experimental challenge: accessing vibrational and electronic signatures of air-sensitive GNRs during synthesis and under controlled environments without breaking
vacuum. Once the material has been exposed to air, standard characterization techniques would probe oxidized or chemically modified species rather than the pristine form. Here, we overcome this limitation by developing a home-built ultra-high
vacuum (UHV) Raman platform designed to preserve sample integrity by preventing air exposure and to enable in situ investigation of material properties. The portable Raman
vacuum suitcase (RVS) integrates temperature control and precise gas dosing, allowing direct monitoring of growth kinetics,
lattice dynamics, and reactive-edge responses under well-defined thermal and chemical environments. Using this platform, we monitor the on-surface synthesis of 7- and 9-atom-wide armchair GNRs (7- and 9-AGNRs), quantify the
evolution of 7-AGNR Raman modes over a wide temperature range (162-748 K), and resolve chemical changes upon controlled O2 exposure that are consistent with oxidation at the reactive zigzag sites. These results establish UHV Raman spectroscopy with the RVS as a route to accessing the intrinsic vibrational signatures of low-dimensional
quantum materials under controlled environments.
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All authors Jeong Ha Hwang, Amogh Kinikar, Lukas Rotach, Andres Ortega-Guerrero, Carlo A. Pignedoli, Klaus Muellen, Thorsten G. Englmann, Xinliang Feng, Pascal Ruffieux, Roman Fasel, Mickael L. Perrin, Gabriela Borin Barin
Materials Science
High-Throughput Imaging of Degradation-Inducing Microscopic Impurities in Perovskite Solar Cells
Sofiia Kosar, Anil R. Pininti, Vladyslav Hnapovskyi et al. (+6 more)
The scalable fabrication of high-quality, large-area perovskite thin films is hindered by microscopic inhomogeneities, particularly residual compositional impurities formed during processing. Identifying these impurities, understanding their impact on device operation, and enabling their rapid detection are essential for upscaling perovskite solar
cells (PSCs). Here, nano-
Fourier transform infrared spectroscopy combined with high-resolution optical and scanning probe techniques was used to identify detrimental impurities in wide-bandgap perovskite films relevant to tandem solar
cells. Photo-stress experiments revealed that degradation of the perovskite layer initiates at impurity-perovskite interfaces, demonstrating that impurities act as failure nucleation sites. Leveraging these insights, a rapid, non-invasive, and high-throughput framework based on high-resolution reflected light microscopy and machine learning-supported image analysis was developed, enabling detection and quantification of harmful impurities in as-prepared films within seconds. Films with higher impurity density show accelerated early degradation, establishing this parameter as an early-warning metric for stability screening. Extending this framework to degradation tracking further reveals coupled photo- and thermo-chemical contributions to impurity-mediated instability. Overall, this work establishes a practical chemically-validated diagnostic imaging framework for rapid pre-screening of perovskite films to enable stable and scalable PSCs.
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All authors Sofiia Kosar, Anil R. Pininti, Vladyslav Hnapovskyi, José P. Jurado, Subhashri Mannar, Lorenzo Mardegan, Anand S. Subbiah, Frédéric Laquai, Stefaan De Wolf
Materials Science
Pressure-induced s,p-d electron redistribution accompanies structural transformation in amorphous Zr-Cu alloy under compression
P. Dziegielewski, J. Antonowicz, K. Georgarakis et al. (+6 more)
Extreme compression can reorganize atomic valence states, in some regimes driving charge from spatially extended orbitals into more compact ones. We investigate this effect in amorphous Zr67Cu33 metallic glass by combining high-pressure X-ray absorption fine structure measurements up to 69 GPa with molecular dynamics simulations and density functional theory calculations. The Zr K-edge XANES spectra show a pronounced increase in the pre-edge intensity and a change in its pressure dependence, whereas the Cu response is markedly weaker. Molecular-dynamics simulations reproduce the measured EXAFS spectra and provide reliable input for the electronic-structure calculations. The calculated Mulliken populations reveal pressure-induced depletion of Zr s and p-states, accompanied by an increase of the d-state population, while the density of states indicates enhanced p-d hybridization under compression. These results provide experimental and computational evidence for pressure-induced s,p-d electronic redistribution in zirconium and link this effect to the previously reported anomalous structural
evolution of the compressed amorphous
alloy.
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All authors P. Dziegielewski, J. Antonowicz, K. Georgarakis, O. Lord, M. Amboage, D. Daisenberger, L. Clough, T. Irifune, T. Shinmei
Materials Science
Machine-learning-guided exploration of domain walls in the hybrid improper ferroelectric Ca3Ti2O7
Ida C. Skogvoll, Erik Fransson, Leo Ö. Westin et al. (+4 more)
Ruddlesden-Popper phases are highly tunable and naturally layered structures, in which polarization can arise via a hybrid improper ferroelectric mechanism. This enables a complex domain wall (DW) structure where multiple order parameters, like octahedral rotations, polar distortions and strain, interact. In this work, we explore the rich set of DW structures in prototypical Ca3Ti2O7, mapping out the DWs in the {100}, {110} and {001} pseudo-tetragonal planes using group theory and machine-learned interatomic potentials (MLIPs). The trained potential reproduces the density functional theory (DFT) order parameter and polarization profiles for all wall types and orientations considered. A charge-aware training framework combined with reference Born effective charges reduces the prediction errors for the DW formation energies by 70%, revealing the importance of including long-range electrostatics to model
symmetry-broken interfaces. Finally, the MLIP is used to identify minimum energy pathways at the atomic scale with nearly the precision of DFT calculations, revealing a low-energy antipolar configuration for polarization switching.
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All authors Ida C. Skogvoll, Erik Fransson, Leo Ö. Westin, Benjamin A. D. Williamson, Nicholas C. Bristowe, Sverre M. Selbach, Paul Erhart
Materials Science
First Principles Magnetic Initialisation Made Simple
Kit D. Brown and Robert A. Lawrence
A fundamental issue with first principles electronic structure calculation is the requirement for
magnetic initialisations, which are usually derived from experimental results. In this paper, we present a new and computationally inexpensive method to predict
magnetic structures from first principles, based upon
symmetry analysis and a non-
magnetic band structure only. We demonstrate that this method of creating initialisations successfully reproduces the known
magnetic ground state for a wide class of
magnetic materials, including ferromagnetic BCC Fe, antiferromagnetic L1$_0$ PtMn, and frustrated antiferromagnetic L1$_2$ IrMn$_3$, while also predicting non-
magnetic materials to remain non-
magnetic.
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Materials Science
Optimization of InAs/InAlGaAs/InP quantum dots for O-band laser applications
Anna Penkała, Paweł Podemski, Vinayakrishna Joshi et al. (+3 more)
The O-band telecommunication spectral range combines minimal chromatic dispersion with low transmission loss, making it highly suitable for optical communications.
Semiconductor telecom
lasers utilizing low-dimensional active regions, such as
quantum dots, offer low threshold power and high thermal stability. However, long-wavelength
quantum dot emitters often suffer from thermal carrier escape through excited states when the energy separation between the ground and excited states is insufficient. Here we demonstrate the optimization of InAs
quantum dot emitters grown on InP by molecular-beam epitaxy for O-band
laser active regions. By optimizing the design for better carrier capture efficiency and tuning the emission wavelength to the O-band, we show ways of improving the carrier confinement. Absorption spectroscopy on the finalized structure confirms substantial energy separation between the
quantum dot ground and excited states, effectively suppressing thermal carrier escape even at elevated temperatures. These results highlight critical design for improving carrier capture and retention in long-wavelength
quantum dot
lasers.
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All authors Anna Penkała, Paweł Podemski, Vinayakrishna Joshi, Vitalii Sichkovskyi, Johann P. Reithmaier, Grzegorz Sęk
Materials Science
Chemical site bases and average-atom potentials for the atomic cluster expansion
Lorenzo Piersante and Anirudh Raju Natarajan
Interatomic potentials are central tools in the atomistic modeling of materials. The atomic cluster expansion (ACE) parameterizes such potentials from ab initio data, conventionally encoding the chemical degrees of freedom with a one-hot representation that yields chemically stratified models. The alternative chemical representations used in on-
lattice configurational cluster expansions have not been assessed for interatomic potentials. Here we revisit the multicomponent ACE for an arbitrary chemical site basis. We then establish an exact analytical mapping between a fitted linear ACE and the average-atom potential that describes a perfectly random
alloy. We
benchmark potentials built on the occupational, Chebyshev, and conventional ACE bases against solute binding and vacancy formation energies in Mg-Nd, and against the mixing enthalpies of the Mo-Nb and Cr-W solid solutions. When training data are scarce, the occupational basis converges fastest and offers the best control over targeted material properties, while the conventional and Chebyshev bases face challenges in reproducing these properties. The occupational basis likewise yields the most reliable average-atom description of disordered
alloy thermodynamics. In the large-data limit the three bases perform identically. The chemical basis is therefore a design choice that governs data efficiency. Its explicit treatment opens a route to average-atom potentials for the thermodynamic, mechanical, and kinetic properties of concentrated
alloys.
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Materials Science
Phase compositions of Si oxynitride: A comprehensive thermodynamic modeling study
Andrey Sarikov, Mariia Babiichuk, Mariia Voitovych et al. (+1 more)
In this work, a comprehensive thermodynamic description of the formation of phases in amorphous SiOxNy (0 <= x <= 2, 0 <= y <= 4/3) films as a function of the film chemical composition and fabrication temperature is presented. Two possible phase states, namely homogeneous single-phase Si oxynitride and two-phase mixture of Si oxide and Si nitride phases, are analyzed in terms of the lowest values of the Gibbs free energy. The characters of the modification of the phase composition upon changing the SiOxNy stoichiometry indices and fabrication temperature are determined. Moreover, characteristic features of the chemical composition of the Si oxide and Si nitride phases in two-phase Si oxynitrides are revealed. Particular
attention is given to the thermodynamic origin of the boundaries between different phase states of the SiOxNy films and to determining the critical stoichiometry values separating them. A comprehensive phase diagram indicating single- and two-phase SiOxNy regions as functions of the fabrication temperature is constructed. The peculiarities of the transitions between different SiOxNy phase states, along with underlying mechanisms, are discussed with reference to this phase diagram. The obtained results extend our understanding of the fundamental properties of Si oxynitride films and their dependence on the film fabrication conditions, and may be used for tailoring SiOxNy characteristics for practical applications.
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All authors Andrey Sarikov, Mariia Babiichuk, Mariia Voitovych, Sergii V. Mamykin1
Materials Science · Cross-listed from cond-mat.str-el
Quantum-Geometric Amplification of Nonperturbative Interaction Scales
Stefano Bilamour, René Meyer, Johanna Erdmenger et al. (+1 more)
Weak interactions at a two-dimensional quadratic band touching (QBT) can generate an exponentially small
symmetry-breaking gap, $m\sim e^{-A/V_1}$, that cannot be captured by every finite order of perturbation theory. We show that the singular
quantum geometry of the gapped QBT converts this beyond-all-orders scale into an algebraically enhanced response. The
quantum metric develops a momentum-space hot spot whose Brillouin-zone integral diverges logarithmically, and therefore grows algebraically when the gap is dynamically generated by interactions. Through the inverse-frequency Souza–Wilkens–Martin optical sum rule, the same amplification appears in the negative-first longitudinal optical moment, even though the ordinary optical conductivity remains $O(e^2/\hbar)$ and its absorption threshold is exponentially small. We establish these results analytically for a massive QBT and verify them microscopically in an interacting kagome
lattice model known to develop a spontaneous
quantum anomalous Hall mass at its QBT from loop currents order. Our results identify
quantum geometry as an asymptotic amplifier of nonperturbative interaction scales.
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All authors Stefano Bilamour, René Meyer, Johanna Erdmenger, Domenico Di Sante