Materials Science · Cross-listed from cond-mat.str-el
Spectral signatures of spin textures and the emergence of a pseudogap
Matteo Quinzi, Andrea Pintus, Tommaso Chiarotti et al. (+2 more)
Periodic solids with strongly interacting electrons display phenomena – from Mott localization to high-temperature superconductivity – that escape conventional band theory. Efforts to address this unconventional physics have been typically cast in the
language of Green's function theories and the associated frequency- and momentum-dependent self-energies capturing strong correlations beyond the reach of mean-field theories. Here, we underscore that frequency- and momentum-dependent self-energies emerge also from mean-field solutions that break translational
symmetry, and that these self-energies can display the characteristic fingerprints of strong correlations for certain, physically meaningful, spatial patterns. We showcase this perspective by studying the paradigmatic case of the 2D Hubbard model. We find that already at the mean-field level the doped antiferromagnet displays, in addition to stripes, many quasi-degenerate self-consistent solutions with antiferromagnetic textures organized into antiphase domains separated by hole-rich interfaces, reminiscent of the phase-separation scenario. Remarkably, these solutions map into spectral functions that display very distinctively the phenomenology of the pseudogap, including the nodal-antinodal dichotomy of the self-energy, Fermi arcs, and a complementary Luttinger surface. The result is a conceptually simple description of such an intricate many-body state: the pseudogap emerges as the momentum-space spectral portrait of the real-space interplay between antiferromagnetic domains and the metallic interfaces, which echoes the role of
spin-fluctuations identified by nonperturbative methods.
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All authors Matteo Quinzi, Andrea Pintus, Tommaso Chiarotti, Massimo Capone, Nicola Marzari
Materials Science · Cross-listed from math-ph
On the Mathematical Structure of Helical Shear in Anelastic Continua
Souhayl Sadik, Giuseppe Saccomandi and Luigi Vergori
We study helical shear of a thick-walled tube made of an incompressible, isotropic hyper-anelastic solid carrying a radially symmetric distribution of axial screw dislocations. Through the Bilby–Kröner–Lee decomposition, the dislocations are encoded in a Weitzenböck material
manifold, whose Riemannian metric alone enters the elastic response.
Equilibrium reduces at each radius to an algebraic system for the azimuthal and axial shear strains, whose cross terms are proportional to the dislocation strength and to the dependence of the strain energy on the second invariant; the two shear modes therefore couple only in the presence of dislocations. Exact solutions are obtained for neo-Hookean, Fung–Demiray, Gent, Knowles, and Mooney–Rivlin materials, and numerical ones for Gent–Gent materials. The universal relations of Horgan and Saccomandi are extended to dislocated generalized neo-Hookean tubes. Dislocations stiffen the tube when the strain energy stiffens with the first invariant, couple the two shear modes chirally when it depends on the second, and may restrict admissibility: they cap the dislocation strength in Gent and Gent–Gent materials, and contract the admissible traction region in Knowles materials with power-law index below n = 1/2. A weakly nonlinear analysis to third order in the applied tractions and dislocation strength shows that, at first order (linear elasticity), the dislocations leave the shear response unaffected while carrying a residual stress. The chiral coupling enters at second order, through the dependence of the strain energy on the second invariant, so that every dislocated material couples the modes as the Mooney–Rivlin solid with the same second- and third-order moduli. At third order, no new coupling arises; the modes interact through stiffness corrections involving the fourth-order modulus, which the dislocations further correct mode by mode.
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Materials Science · Cross-listed from math-ph
On optimal Wannier decay in dimension three
Simon Becker, Zhongkai Tao and Mengxuan Yang
For a Chern nontrivial Bloch bundle over the three
torus, we construct an orthonormal Wannier basis with the optimal pointwise decay $\mathcal{O}(|x|^{-5/2})$. All but one of the generators decay exponentially. This resolves the question left open in arXiv:2505.01999.
Materials Science
Symmetry-selected extreme shear compliance in a stable carbon monolayer
J. W. González, M. Pachecho and J. D. Correa
Solids that are stiff to most loads and extremely compliant to one are normally built, not found. That internal atomic relaxation lowers elastic constants is textbook; what has remained untested is whether it can be driven far enough to separate the elastic scales of a
crystal by an order of magnitude while leaving it mechanically stable. Density functional theory calculations of the complete in-plane elastic tensor of four non-hexagonal carbon monolayers sharing a square
lattice metric show that it can: their longitudinal stiffnesses agree to within a factor of two while their shear constants span more than a factor of fifty. Twin T-
graphene, previously reported as elastically isotropic from normal strains alone, is the extreme case, with $C_{66}=3.03$~N\,m$^{-1}$, nearly fifty times below
graphene, at an axial stiffness typical of semiconducting monolayers, and a soft Kelvin
eigenvalue a factor of $29$ below the others while the Born criteria hold.
Symmetry confines the strain-induced relaxation to the $B_{2g}$ sector, a counter-torsion of the carbon sublayers about the short mid-plane bonds that removes $96\%$ of the clamped-ion shear stiffness with almost no bond stretching and leaves the semiconducting gap intact. Transverse acoustic
phonons, finite-temperature dynamics, and large-deformation simulations show that the channel survives beyond the harmonic, zero-temperature limit. Because the selection rule is a point-group statement rather than a chemical one, it yields a screening criterion for other
crystals and other strain components.
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Materials Science
Engineering Correlated Transparent Conductors via Metal-Insulator Transition Proximity
Amit Cohen, Nofar Tuval, Maria Baskin et al. (+5 more)
Transparent conductors are key functional materials in modern optoelectronic devices. Their performance is governed by an inherent trade-off between optical transparency and electrical conductivity. Correlated metallic oxides offer an attractive workaround to this compromise, where narrow partially-filled bands provide high conductivity, while the absence of visible-range transitions enables optical transparency. Despite this promise, transparency and conductivity remain coupled through carrier density and electronic coherence. Here, we use proximity to a metal-
insulator transition (MIT) as a design principle for engineering this balance in correlated-oxide transparent conductors. Epitaxial Ti-substituted $SrVO_3$ films serve as a model platform where the optical window and
metallicity are tuned simultaneously. We demonstrate and explain a systematic broadening of the optical window to regimes relevant for silicon photovoltaics. This gain is counterbalanced by carrier depletion and disorder, which drive the loss of coherent transport near the composition-driven MIT. A Haacke figure-of-merit analysis identifies the optimal composition range near the MIT, where the loss of metallic transport is accompanied by persistent near-Fermi-level spectral weight, indicating disorder-assisted localization together with correlation-driven spectral-weight redistribution. These findings establish proximity to an MIT as a general materials-design strategy, using electronic filling as a tuning knob for the transparency-conductivity balance in correlated-oxide transparent conductors.
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All authors Amit Cohen, Nofar Tuval, Maria Baskin, Tien-Lin Lee, Tom Tiwald, Scott A. Chambers, Sophie D. Beck, Lior Kornblum
Materials Science · Cross-listed from cond-mat.other
A Conservative Darcy-Brinkman-Stokes Formulation for PHREEQC-Coupled Reactive Transport with Cell-Based Surface Complexation
Hannah P. Menke, Florian Doster and Julien Maes
We present a mass-conservative Darcy-Brinkman-Stokes (DBS) formulation for reactive transport with
cell-based surface complexation in image-based porous media, coupled to PHREEQC and implemented in GeoChemFoam, an OpenFOAM-based toolbox. Dissolved species are transported in the physical mobile-water fraction, adsorbed species are stored as conservative
cell-scale surface inventories, and each reactive
cell is coupled to PHREEQC. Reactive surface area is prescribed independently as a
cell field, so that internal area left unresolved by segmentation of microporous phases can be represented while DBS flow and transport are retained in the resolved pore space. The implementation is verified with a test suite that isolates the coupling of transport and chemistry from the construction of reactive surface area. Aqueous and adsorbed mass balance is evaluated against a one-dimensional analytical retardation
benchmark and closed-system batch calculations. The smooth-interface surface-area
algorithms are tested on idealised two- and three-dimensional geometries. In a two-scale lithium micromodel, DBS reproduces fully resolved aqueous and sorbed inventories within 0.6% across Pe=0.1-10. The applications comprise Pb2+ retardation by hydrous ferric oxide coatings in a two-dimensional fracture network, competitive Mn2+/Mg2+ exchange in a three-dimensional Kelvin-
cell sorbent, and Sr2+/Ca2+ exchange in Estaillades limestone. In the fracture-network and limestone cases, the formulation yields spatially resolved aqueous and adsorbed inventories even where reactive surface area is only partly resolved at the image scale. The framework therefore supports conservative surface-complexation modelling in both resolved and unresolved pore structures, with relevance to contaminant retention, selective ion capture, and radionuclide transport.
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Materials Science · Cross-listed from cond-mat.mes-hall
Topological superconductivity in layered d-wave altermagnetic metals
Yijie Mo and Zhongbo Yan
We investigate multilayer d-wave altermagnetic metals with odd-parity helical p-wave pairing. In the minimal bilayer system, interlayer tunneling reconstructs the
spin-split Fermi surfaces and generates two layer-hybridized sectors with distinct effective chemical potentials. Without Rashba
spin-orbit coupling (RSOC), the emergent mirror
symmetry and subsystem chiral
symmetry stabilize phases with different numbers of helical Majorana edge-mode pairs and additional counterpropagating pairs, jointly characterized by the mirror Chern number and the winding numbers defined along high-
symmetry lines. The combination of RSOC and the altermagnetic exchange field gaps out the helical Majorana pairs while, in a certain parameter regime, leaving another pair of counterpropagating Majorana edge modes gapless, giving rise to second-order topological phases with isolated or twofold Majorana corner modes, as well as a hybrid-order phase in which gapless Majorana edge modes coexist with Majorana corner modes. We identify a layer
symmetry that elucidates the physical origin of these phases. For an arbitrary N-layer system, such a
symmetry naturally arises from the interlayer-coupling
matrix, allowing N-fold Majorana corner modes to emerge when all layer-hybridized sectors enter the nontrivial second-order regime. Our results establish the interplay among the layer degree of freedom, odd-parity pairing, and Fermi-surface configurations as a controllable route to engineering topological superconductivity in layered altermagnetic systems.
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Materials Science
Electron-Mediated Phonon Polaritons in Quantum Cavities
Mattia Udina, David Hagenmüller and Indranil Paul
Phonon-
photon coupling in
quantum materials is commonly treated as an effective direct interaction, neglecting the crucial role played by electrons. Here we develop a gauge-invariant theory of cavity
phonon polaritons that captures electronic screening, dissipation, and hybridization. We show that screening can suppress polariton formation in metals, severely constraining cavity control of
phonon-mediated superconductivity. By contrast, interband electronic resonances in time-reversal-symmetric gapped systems can strongly enhance
phonon-
photon coupling, enabling robust polariton formation down to the monolayer limit despite electronic absorption. We illustrate these effects in NbSe2, hBN, and gapped
graphene. Finally, we show that gauge invariance enforces
photon decoupling from a critical soft
phonon, establishing a general no-go mechanism for
photon condensation.
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Materials Science
Virtual-Alloy Physics-Aware Semantic System for extrapolative prediction of perovskite solar cells
Qiwei Han and Chi Zhou
Existing machine-learning models for perovskite solar
cells struggle to predict devices made from new materials. Most treat device layers as arbitrary categorical labels and represent perovskite absorbers either through featureless composition vectors or through rigid
crystal graphs that require a pre-solved unit
cell. As a result, they cannot generalize to unrecorded
alloys or unfamiliar
cell architectures. We present the Virtual-
Alloy Physics-Aware Semantic System (V-PaSS), an architecture built around the physical continuity of perovskite solid solutions. V-PaSS represents arbitrary mixed-cation, mixed-halide absorbers by interpolating relaxed
crystal graphs of 23 pure $ABX_3$ endpoint compounds via Vegard's law with learned bandgap bowing. For the device stack, it couples layer sequence and
cell polarity (n-i-p or p-i-n) with interfacial band offsets and encodes chemical descriptions with a scientific
language model. Evaluated under an institution-grouped protocol where test devices come exclusively from unseen laboratories, an untuned default configuration of V-PaSS achieves the lowest error among fourteen tested models (2.861% MAE, a 5.2% relative reduction over a gradient-boosted baseline at 3.017%, and outperforming the best tuned
benchmark at 2.912%). V-PaSS pulls furthest ahead where test devices differ most from training: reducing error by 15.7-19.0% on unseen absorber
alloys, by 16.1% on mixed absorbers from new laboratories, and widening its lead over the baseline by 3.6$\times$ on devices with unobserved transport layers. Combined with tree ensembles, V-PaSS sets a new state of the art across all five
benchmark splits.
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Materials Science · Cross-listed from cond-mat.str-el
Superexchange coupling between a dilute Gd3+ probe and orphan spins in a valence-bond glass
Patrick Colgan, Artur Solodovnyk, Jeremy P. Carlo et al. (+1 more)
The valence-bond-glass state of the 4d^1 double perovskite Ba2YMoO6 combines Mo^5+ singlets with residual paramagnetic "orphan"
spins whose coupling is hard to reach with bulk probes. We probe them by electron paramagnetic resonance of a dilute Gd^3+ ion on the Y^3+ site via broadband coplanar-waveguide transmission at 5 K. The isostructural nonmagnetic niobate Ba2YNbO6, doped with the same Gd^3+ probe, is a fixed-
lattice control. The Gd^3+ linewidth nearly doubles in the
magnetic host. Dipolar coupling to the sparse orphans is nearly an order of magnitude too weak; the excess is instead reproduced by a transferred f-d superexchange of J ~ 0.2 K, so the width is a static measure of orphan-
spin coupling. The half-field (Delta m_S = +/-2) satellite collapses in the
magnetic host, a dynamical dephasing channel, while the unchanged g-factor marks a zero-mean random internal field. Together the two channels probe the coupling and dynamics of valence-bond-glass orphan
spins.
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All authors Patrick Colgan, Artur Solodovnyk, Jeremy P. Carlo, Scott Dietrich
Materials Science
Composition-controlled optical fingerprints and anisotropy of self-trapped excitons in double perovskites
Simone Grillo, Offir Zachs Maishlos, Liya Koren et al. (+7 more)
Double perovskites (DPs) offer a compositionally versatile platform for photocatalysis and optoelectronics, but their soft
lattices favor strong
exciton-
phonon coupling and self-trapped
excitons (STEs), which produce broad, red-shifted photoluminescence (PL). Here, we combine optical spectroscopy and ab initio calculations to study lead-free, Sb-doped Cs2BInCl6 nanocrystals with B-site alloying from Na to K. Alloying tunes the PL energy from about 2.48 to 2.70 eV, while absorption features near 3.8 eV remain nearly unchanged. Calculations reveal that Sb doping enables bright radiative recombination channels and delocalizes the excitonic wavefunction. We identify STEs responsible for the large PL red shift, associated with an upward shift of dopant-hybridized in-gap states. Na-to-K substitution selectively changes the STE
lattice distortion, explaining why PL varies strongly with composition while absorption does not. Theory further predicts pronounced PL polarization anisotropy that reflects the STE wavefunction's spatial structure and depends on B-site composition. Time-resolved anisotropy measurements closely agree with these predictions, providing experimental fingerprints of the excitonic wavefunction and its
evolution with alloying. Together, these results disentangle the roles of doping and alloying in lead-free DPs and establish polarization-resolved spectroscopy as a probe of STE wavefunctions.
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All authors Simone Grillo, Offir Zachs Maishlos, Liya Koren, Rotem Strassberg, Rachel Lifer, Edi Maizenberg, Umberto De Giovannini, Angel Rubio, Yehonadav Bekenstein, Ofer Neufeld
Materials Science
Time-Resolved Phonon Dispersions of Thermally Excited Graphite at the Nanoscale
Mairi McCauley, Christoph T. Koch and Benedikt Haas
Lattice vibrations govern the propagation of heat in materials, and investigating their dynamics through time-resolved
phonon dispersion measurements would provide insight into these excitations and their interactions. However, time-resolved measurements that directly resolve the
phonon dispersion at the nanoscale have not been previously demonstrated. Momentum-resolved vibrational electron energy loss spectroscopy (EELS) provides access to
phonon energies and momenta with nanoscale spatial resolution. Here, we combine momentum-resolved vibrational EELS with pulsed
laser heating and synchronised gated electron detection to observe the
phonon dispersion of graphite during controlled heating and cooling on the microsecond timescale. Recording both the gain and loss spectra at defined times relative to
laser excitation, we determine the temperature at each time delay and follow changes to the
phonon branches as a function of temperature. The momentum-resolved spectra reveal a decrease in energy of the optical
phonon branch with increasing temperature accompanied by an increase in peak width. These changes are consistent with temperature-dependent
phonon renormalisation and scattering associated with anharmonic interactions. The approach is compatible with detector gating on timescales down to 50 ns, providing a route towards extending these measurements to faster dynamics. This work demonstrates time-resolved
phonon dispersion spectroscopy using vibrational EELS and provides a route towards probing temperature-dependent
phonon dynamics at the nanoscale with simultaneous energy and momentum resolution.
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Materials Science
Direct growth of crystalline spinel GaON films: A wide-bandgap mixed-anion semiconductor
Baikui Li, Zecheng Yang, Wenhao Yin et al. (+5 more)
Mixed-anion
semiconductors offer opportunities for bandgap engineering beyond conventional multication
alloys, but competing phases and disorder complicate their synthesis and the identification of their electronic properties. Gallium oxynitride (GaON) could connect the technologically important GaN and Ga2O3 systems, yet establishing a clear relation between its
crystal structure, composition and bandgap remains challenging. Here we report the direct growth of crystalline spinel gamma-GaON films by nitrogen-
plasma-assisted pulsed-
laser deposition. Varying the nitrogen and oxygen supply yields monoclinic beta-Ga2O3, predominantly disordered films and crystalline spinel GaON. Complementary diffraction, atomic-resolution microscopy and elemental analysis establish the spinel structure and nitrogen incorporation. Temperature-dependent photocurrent spectroscopy reveals a clear
redshift of the crystalline gamma-GaON response, supporting assignment of a band-edge transition near 4.3 eV at room temperature. These results open opportunities to investigate mixed-anion wide-bandgap
semiconductor physics and develop
heterostructures.
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All authors Baikui Li, Zecheng Yang, Wenhao Yin, Zijing Wu, Haitao Zhao, Yunwei Sheng, Honglei Wu, Jiannong Wang
Materials Science
A Transferable Machine-Learned Potential Enabling Large-Scale Copper-Carbon Simulations from Equilibrium to Extreme Conditions
Feiyu Zhou, Wei Qiu, Yan Chen et al. (+4 more)
Cu-C materials and interfaces are central to diamond thermal management, metallization,
graphene growth and carbon-coating technologies, but atomistic simulations across these applications require a potential that describes metallic Cu, diverse carbon bonding, heterogeneous Cu-C interactions and close atomic encounters. Here we develop NEP-CuC, a transferable neuroevolution potential trained on a
dataset of 2,727 uniformly relabelled configurations selected from a heterogeneous Cu-C candidate pool. Disagreement within an ensemble of five independently trained models provides an internal indicator of model sensitivity. A Ziegler-Biersack-Littmark (ZBL) correction describes short-range nuclear repulsion, while a runtime D3(BJ) correction supplements dispersion-sensitive calculations. Tests on source-derived held-out and independent external
datasets, together with structural, elastic, defect, interfacial, vibrational and finite-temperature transport
benchmarks, establish broad but property-dependent physical fidelity across elemental Cu, diverse carbon environments and heterogeneous Cu-C configurations. Large-scale simulations of amorphous-carbon formation and orientation-dependent shock compression of Cu further test transferability under strongly non-
equilibrium conditions. For Cu/diamond interfaces, the same potential describes deposition, annealing and tensile response: preparation history leaves persistent differences in interphase structure, while the mean peak nominal tensile stress at 500 K decreases from $12.35\pm0.71$ to $6.65\pm0.98$ GPa as the incident Cu energy during the initial deposition stage increases from 1 to 50 eV. NEP-CuC provides an atomistic framework for linking processing, interfacial structure and physical response across Cu-C systems, with direct relevance to Cu/diamond thermal-management interfaces, diamond metallization and non-
equilibrium Cu-C processing.
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All authors Feiyu Zhou, Wei Qiu, Yan Chen, Jiahui Liu, Yilun Liu, Shengying Yue, Penghua Ying
Materials Science
Imaging Gate-Tunable Single-Layer Molecular Kagome Lattices
Ziyi Wang, Rafal Zuzak, Weichen Tang et al. (+11 more)
Kagome
lattices provide a simple geometry for engineering electronic states that exhibit novel
quantum behavior. In conventional kagome materials, however, the relevant states are often embedded in chemically complex three-dimensional
crystals and are difficult to isolate or tune. Molecule-based kagome networks offer structural precision and tunability, but have largely been confined to metallic substrates incompatible with 2D devices. Here we report growth of single-layer Ni$_3$(HITP)$_2$ metal-organic frameworks (MOFs) on van der Waals substrates including
graphene-based field-effect devices using metal-salt molecular beam epitaxy. Low-temperature scanning tunneling spectroscopy resolves kagome-derived flat-band and van Hove singularity-based spectral features consistent with first-principles calculations. Gating hybrid 2D MOF devices allows us to energetically shift kagome spectral features, thus establishing electrostatic control of chemically programmable 2D kagome electronic
lattices.
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All authors Ziyi Wang, Rafal Zuzak, Weichen Tang, Haowen Pang, Yutang Qiao, Dhanvanth Balakrishnan, Yuqiao Yan, Aining Hu, Andrew Sun, Takashi Taniguchi, Kenji Watanabe, Feng Wang, Steven G. Louie, Michael F. Crommie
Materials Science
Flexoelectricity and Flexomagnetism
Alexander Edström and Massimiliano Stengel
Strain gradients, unlike homogeneous strain, are odd under space inversion and unlock couplings that are strictly forbidden in the parent
crystal. At the nanoscale, and in curved low-dimensional systems in particular, such gradients are readily attainable and often unavoidable, so that
curvature acts as a
symmetry-breaking field written into the
lattice itself. This chapter reviews the resulting couplings to electric polarization and magnetism. After establishing the
geometric relation between strain gradients and
curvature, we review flexoelectricity as the better-established reference case: the bulk, surface and dynamic contributions that complicate its definition, its microscopic mechanisms, its manifestation in two-dimensional materials, and the first-principles methodology now available for its calculation. Using the magnetoelectric effect as a conceptual bridge, we then develop flexomagnetism in a broad sense, covering any coupling phenomena between magnetism and strain gradients, and specifically discuss the linear magnetization response to
curvature and
curvature-induced Dzyaloshinskii-Moriya interactions, beyond the established curvilinear treatment. Finally, we briefly describe some additional effects fitting under this broad umbrella of flexomagnetism, including nonlinear ones, inhomogeneous magnetoelectric and Rashba-type phenomena, and connections to altermagnetism.
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Materials Science
Quantitative Modelling of Solvation in 2D Materials via Alchemical Decoupling and Potential Energy Surfaces
Lindsey N. Ioos, Duncan A. Peterson and Scott C. Warren
Understanding why 2D materials remain suspended in solutions is essential to understanding the mechanisms of aggregation and exfoliation. These dynamics have been difficult to model because of the long timescales and large activation energies involved in these simulations. Here we describe an improved strategy for modelling the solvation and stability of 2D materials that uses the Gibbs free energy of solvation to accurately calibrate two disconnected potential energy surfaces for the fully desolvated and fully solvated 2D materials. By joining these surfaces using solvation energy, we obtain predictions for 2D material stability in various solvents that are qualitatively different than prior simulations and that have excellent agreement with experimental results. Our approach predicts a much higher barrier to full desolvation of the material, suggesting that materials that appear to be aggregated in fact still retain monolayers of solvent between adjacent layers of 2D materials. This work provides much needed understanding on the interactions between the solvent and 2D material that can guide future experimental work.
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Materials Science
Substrate-controlled epitaxial-like growth of photochromic yttrium oxyhydride thin films
M. Zubkins, E. Strods, E. Letko et al. (+7 more)
Yttrium oxyhydride (YHO) thin films are synthesised by reactive magnetron sputtering of e̱ta}-YHx precursor films onto single-crystalline yttria-stabilised zirconia (YSZ) (111) and (100) substrates at 200 {\deg}C, followed by post-deposition oxidation in air. For comparison, reference films are also prepared on amorphous SiO2 and soda-lime glass substrates at both 200 {\deg}C and room temperature (RT). The structural (X-ray diffraction and scanning electron microscopy), compositional (elastic recoil detection analysis), and optical properties, including photochromic behaviour, of the films are systematically investigated. The results reveal a strong influence of substrate orientation on the film microstructure and crystallographic texture, leading to epitaxial-like growth with a mosaic spread of ~3-4{\deg}. YHO deposited on YSZ(100) exhibits larger crystallite sizes (10-20 nm) than YHO grown on YSZ(111) (~8 nm) and exhibits residual in-plane compressive strain while remaining largely relaxed with respect to the substrate. Compositional analysis revealed that the O/Y and O/H atomic ratios ranged from 0.71 to 0.82 and from 0.33 to 0.44, respectively, for films deposited under optimised conditions. These films exhibit photochromic behaviour under solar simulator illumination, with relative transmittance changes ranging from 7 to 22 % after 10 min of illumination. Despite the pronounced structural differences, the epitaxial-like films show no systematic improvement in photochromic response, indicating that the effect is governed primarily by composition. The study shows that the bleaching time constant increases exponentially with increasing contrast reached during illumination, rather than representing an intrinsic material constant of YHO.
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All authors M. Zubkins, E. Strods, E. Letko, H. Mändar, D. Moldarev, K. Mizohata, K. Sarakinos, V. Vibornijs, K. Kundzins, J. Purans
Materials Science
Reversible Magneto-ionic Modification of Metallic Magnetic Thin Films
Md Golam Hafiz, Hari Babu Vasili, Philippa Shepley et al. (+12 more)
Magnetic multilayers with structural inversion asymmetry, perpendicular
magnetic anisotropy (PMA), and large Dzyaloshinskii-Moriya interaction (DMI) are widely studied for
magnetic domain wall- and skyrmion-based data processing applications. In this work, we report a controlled, nonvolatile, but reversible local modification of such a system by electrically driven oxygen migration through the metallic film structure by using ionic
liquid gating. Our findings provide direct evidence for the modification of the oxidation state at the heavy metal (HM)/ferromagnet (FM) interface. As a result, we observed changes in fundamental
magnetic properties, such as an increase in the effective anisotropy constant (Keff) and coercive field (Hc) with oxidation, and a decrease with the reduction of oxygen ions. Positive gate voltages relative to the thin film extract oxygen ions from the
magnetic layer, significantly reducing the domain nucleation field. In contrast, negative voltages drive oxygen ions into the
magnetic layer, leading to a reversible increase in the extent of domain wall pinning near saturation. We observe a corresponding decrease in the
magnetic moment and DMI, with negative voltage reducing both. This magneto-ionic modulation in fully metallic structures is beneficial for spintronic device applications, particularly in field-programmable domain wall and skyrmion devices.
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All authors Md Golam Hafiz, Hari Babu Vasili, Philippa Shepley, Mannan Ali, Andrew J. Britton, Oscar Cespedes, Weibin Li, Manuel Valvidares, Rohit Pachat, Wilfried Fotso, Mourad Cherif, Shimpei Ono, Yves Roussigne, Mohamed Belmeguenai, Gavin Burnell
Materials Science
Accurately Generalizing Deep-Learning Hamiltonian Methods to Plane-Wave Density Functional Theory
Chuntian Wu, Jiaxiang Li, Qiang Xu et al. (+4 more)
Deep neural networks that predict density functional theory (DFT)
Hamiltonians from material structures offer a route to efficient electronic-structure calculations. However, extending localized atomic-orbital (AO)
Hamiltonian learning to plane-wave (PW) calculations with hybrid functionals requires a compact AO representation that preserves the effects of nonlocal operators. Here we propose a projectability-guided construction of nonorthogonal AO
Hamiltonians from a small, selected set of PW eigenstates and
eigenvalues. High-projectability states are retained, and selected higher-energy states complete the AO subspace, avoiding an empirical shift and its arbitrary contribution to the learning targets. Because the construction uses PW eigenstates and
eigenvalues, it incorporates nonlocal contributions present in the reference calculation without explicitly reconstructing their AO
matrix elements.
Benchmarks for MoS2 and sodium phases show accurate reproduction of PW bands with smaller AO bases than real-space reconstruction. The resulting PBE and HSE
Hamiltonians can be learned by equivariant neural networks, connecting PW reference calculations with electronic-structure prediction. This approach broadens the range of PW DFT calculations available for AO
Hamiltonian learning and enables compact, accurate training targets for developing more widely applicable electronic-structure models.
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All authors Chuntian Wu, Jiaxiang Li, Qiang Xu, Xuecheng Shao, Congwei Xie, Yu Xie, Yanming Ma
Materials Science · Cross-listed from cs.AI
Complex materials engineering via Provenance Action Graphs: potential, structure and demonstration
Yevgeny Rakita, Paul Todd, James R. Neilson et al. (+1 more)
This work discusses and tests the potential of reaction graphs for material synthesis, in which events consist of reaction steps (actions) and their outputs (observations). The importance comes from the requirement to synthesize technologically useful materials, especially those that are kinetically stabilized. Often, it is a science that follows years of trial and error, culminating in (published) successful recipes, but is truly driven by far more (unpublished) failures. The entry into the era of AI provides an opportunity to use learning
algorithms to encode rules from multi-dimensional synthesis pathways, regardless of their technological usefulness, and to decode both forward prediction and inverse learning modes. The main incentive is to accelerate material discovery by generating a global knowledge base that can be shared among data
agents and contributed to by them. We will focus on several scenarios in the common synthesis process during solid-state synthesis, primarily because these reactions are kinetic in nature and require closer monitoring and control of the reaction history.
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All authors Yevgeny Rakita, Paul Todd, James R. Neilson, Simon J. L. Billinge
Materials Science
Transition-Metal-Induced Uniaxial Anisotropy in YFe$_3$
M. Nur Hasan, Bruno L. Fertig, Santa Pile et al. (+13 more)
Achieving uniaxial magnetocrystalline anisotropy while preserving high magnetization and thermal stability remains a central challenge in the development of Fe-rich permanent magnets. YFe$_3$ is a promising candidate owing to its saturation magnetization and Curie temperature, but its intrinsic easy-plane anisotropy limits its potential for permanent-magnet applications. Here, we show that selective transition-metal substitution drives an easy-plane-to-easy-axis transition in YFe$_3$. Systematic first-principles screening identifies V, Nb, and Ta as effective dopants, with YFe$_{2.33}$Ta$_{0.67}$ exhibiting a large uniaxial magnetocrystalline anisotropy energy of 2.3~MJ/m$^{3}$. Calculated exchange interactions and atomistic Monte Carlo simulations show that the enhanced anisotropy is achieved while preserving robust ferromagnetic order and high thermal stability. Micromagnetic simulations further reveal that YFe$_{2.33}$Ta$_{0.67}$ exhibits the highest coercivity and strongest resistance to irreversible demagnetization, whereas YFe$_{2.33}$V$_{0.67}$ achieves a comparable maximum energy product at 300~K. Experimental characterization of V-alloyed YFe$_3$ shows that the YFe$_3$ phase can be retained at low nominal V concentrations (1-3 at.%) under the employed synthesis and heat-treatment conditions, whereas higher V contents lead to increasingly multiphase samples. Concentration-dependent MAE calculations reveal a sign reversal between approximately 11 and 14~at.% V, marking the transition from easy-plane to uniaxial easy-axis anisotropy. Consistent with this concentration dependence, electron backscatter diffraction and Kerr microscopy reveal in-plane
magnetic domain structures in the experimentally accessible low-V regime. Therefore, our work offers a promising approach to tuning the magnetocrystalline anisotropy of YFe$_3$ while retaining high Curie temperatures.
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All authors M. Nur Hasan, Bruno L. Fertig, Santa Pile, Rafael M. Vieira, Alena Vishina, Alexander Kovacs, Gotthard Rieger, Stefan Denneler, Samuel J. R. Holt, Martin Lang, Swapneel Pathak, Andrea Petrocchi, Hans Fangohr, Thomas George Woodcock, Thomas Schrefl, Heike C. Herper
Materials Science
A Topological Spin on Racetrack Memory
Benjamin Zingsem
Magnetic racetrack
memory requires localized carriers that combine rapid motion, resistance to perturbations and a detectable signal. Here we show how a 360{\deg} domain wall in a hollow ferromagnetic tube combines these properties within a single continuous
magnetic shell. Two successive magnetization reversals form a bound object whose surrounding domains point in the same direction. Analytical energetics and micromagnetic simulations establish its finite separation, recovery from tested perturbations and current driven transport without microscopic Dzyaloshinskii-Moriya interaction or a maintaining field. The texture's winding resists unwinding while radial rotation carries an energy cost, providing a specific control over stability. Relative rotation of the constituent
spins accounts quantitatively for additional displacement during current onset. The wall supports motion at hundreds of metres per second, with transient velocities approaching one kilometre per second at stronger drive. A prepared seven-bit pattern retains its carriers and local readout contrast after pulsed transport and recovery. Curved-track and differential-current tests identify radial stiffness and drive uniformity as controls for intact motion. These results establish a physical basis for fast, locally distinguishable tubular
magnetic bits and identify a continuous switching pathway that can be targeted by tailored excitation.
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Materials Science
Coherent Phonon Generation from Prethermal Carrier Populations in a Semiconductor
Mingyu Shi, Matteo Savoini, Patrick Friebel et al. (+5 more)
Ultrafast
laser excitation of carriers in
semiconductors often results in the creation of fully symmetric coherent optical
phonons, typically understood in terms of a thermalized transient carrier population. We test this understanding with systematic measurements and first-principles calculations of the
photon-energy dependence of ultrafast-
laser-driven coherent
phonon generation in tellurium, using excitation wavelengths around the electronic band gap. We observe that, contrary to the expectations of models assuming a thermalized carrier population, the coherent amplitude of the fully symmetric $A_1$ mode changes only weakly when tuning wavelength across the band gap. The measured spectral dependence is instead reproduced by a transition-resolved prethermal force weighted by optical
matrix elements and band- and momentum-dependent $A_1$ deformation potentials. Fitting this model to the data yields an excited transition state lifetime of a few femtoseconds. These results identify transition selectivity, rather than a thermalized total carrier density, as a key factor controlling coherent-
phonon generation in
semiconductors excited near a band gap.
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All authors Mingyu Shi, Matteo Savoini, Patrick Friebel, Andrea Annunziata, Thomas Metzger, Yunpei Deng, Laura Cattaneo, Steven L. Johnson
Materials Science
MINFF: A Family of Classical Force Fields for Minerals with Tunable Angle Terms
Michael Holmboe, Nathan Lavauzelle and Rogers E. Swai
Atomistic simulations of minerals are limited by the accuracy and transferability of the force field. We introduce MINFF, a force field family for layered and non-layered oxides and hydroxides of M being Si, Al, Fe, Mg, Ca, Ti, Li and F. MINFF has no M-O bond terms. Instead M-O distances follow from electrostatics and dispersion, while a single harmonic angle term on all M-O triplets controls coordination geometry. Metal charges are DDEC6 charges from reference mineral structures, and oxygen charges are assigned by nearest-neighbour charge smearing, covering basal, apical, hydroxyl and edge sites and sites adjacent to isomorphous substitutions. The oxygen Lennard-Jones parameters are based on the OPC3 water model and change by less than 5% when re-optimised per mineral, so compatibility with OPC3 and related ion-pair potentials is measured rather than assumed. Metal Lennard-Jones parameters were fitted to unit-
cell metrics, bond distances and angles, both synchronously across more than 30 reference minerals (general, GMINFF) and for individual minerals (tailored, TMINFF), each at four angle force constants (0, 250, 500 and 1500 kJ/mol/rad^2). With angle terms, MINFF reproduces experimental unit-
cells metrics to within 0.5% and atom-type distances and angles to within 0.7-1.4% and 0.1-0.4%, with Global Instability Index values as low as 0.11, below those of CLAYFF (0.34) and INTERFACE (0.21). A moderate angle constant reproduces the stiff in-plane and soft shear elastic constants of phyllosilicates and improves the Kaolinite librational bands, and in hydrated Na-Montmorillonite MINFF gives the lowest residual factor against the 2W 00l pattern of the models tested. The general and tailored sets at four angle stiffnesses give direct control over the transferability-fidelity trade-off.
Topologies can be generated with the atom (MATLAB) and atomipy (Python) libraries and at www.atomipy.io.
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Materials Science · Cross-listed from cond-mat.str-el
Unexpected stabilization of a single-$q$ charge density wave in pristine 1T-TiSe$_2$
Kimoon Higashihira Han, Dongju Hwang, Dongsin Kim et al. (+16 more)
Over the past decade, studies revisiting the classical charge-density-wave system 1T-TiSe$_2$, long understood to host the $2 \times 2$ triple-$q$ order with equivalent subcomponents, have suggested that these subcomponents may not be identical, challenging a 50-year-old paradigm. Here, we demonstrate not only that these subcomponents are non-identical but also that they develop sequentially rather than simultaneously. By tracking folded-band features, angle-resolved photoemission spectroscopy reveals that a unidirectional $2 \times 1$ single-$q$ order stabilizes first, while the other two components emerge sequentially at lower temperatures, completing the triple-$q$ phase. Our free-energy analysis explains this hierarchy through repulsive coupling among the three subcomponents, as supported by first-principles calculations incorporating
phonon anharmonicity. Consequently, the three subcomponents are inequivalent in both phase and amplitude. These results reconcile reported
symmetry breaking and differing characteristic temperatures and establish a framework in which ostensibly simple, high-
symmetry charge-density order emerges from temperature-dependent competition and cooperation among inequivalent subcomponents.
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All authors Kimoon Higashihira Han, Dongju Hwang, Dongsin Kim, Yeojin Ahn, Jaehun Cha, Seonggeon Gim, Gyubin Lee, Mingi Jho, Chan-young Lim, Sae Hee Ryu, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Jonathan D. Denlinger, Makoto Hashimoto, Donghui Lu, Young Woo Choi, Gil Young Cho, Yeongkwan Kim
Materials Science
Orientation-Resolved Nanoindentation of Single Crystal Ti-15Mo: Inverted Elastic Anisotropy and Yield-Onset Behavior Beyond Simple CRSS Predictions
Kidus Abebe, David Gaetano, Aurelia Moriyama-Gurish et al. (+4 more)
Ti-15Mo (wt%) is a well-established $\beta$-stabilized
alloy whose mechanical response is strongly governed by phase stability and deformation mechanisms that operate at the single-grain scale. Because these intragranular mechanisms are intrinsically anisotropic, understanding the orientation dependence of the elastic and plastic response is critical to the texture-engineered processing of wrought components. Here, we quantify the nanomechanical anisotropy of single-
crystal Ti-15Mo by combining EBSD with nanoindentation to correlate hardness, indentation modulus, strain rate sensitivity, and indentation yield response with the crystallographic surface normal near $\langle111\rangle,\langle124\rangle,\langle011\rangle,\langle023\rangle$, and $\langle013\rangle$ directions. While the modulus anisotropy is small (~10%), contrary to the prediction for a cubic
crystal with A>1, orientations near $\langle111\rangle$ exhibit the lowest moduli. Yield onset is likewise softest near $\langle111\rangle$ and spans 41%, while hardness spans only 6.6% and follows neither the modulus nor the yield ordering. The
alloy also exhibits yield behavior not captured by the simple CRSS/Schmid-factor models evaluated here. Strain-rate-jump tests yield V*=18-31b$^3$, consistent with kink-pair-nucleation-controlled plasticity; based on V*, the orientations separate into two groups suggestive of glide-dominated versus twin/transformation-participating response. We reveal an inversion of the elastic anisotropy expected for a homogeneous cubic $\beta$-phase and an orientation-dependent yield-onset response that is not reproduced by the simple Schmid-factor models examined here. Retained athermal $\omega$ is proposed as the contributor because $\beta\rightarrow\omega$ collapse occurs on {111}$_\beta$ planes and may provide anelastic compliance through the reversible $\omega\rightarrow\beta$ transformation.
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All authors Kidus Abebe, David Gaetano, Aurelia Moriyama-Gurish, Jana Šmilauerová, Yanfei Gao, Udo D. Schwarz, Amit Datye
Materials Science
High-throughput screening of Heusler alloys for thermoelectrics combining machine-learned densities of states and first-principles transport
Shivam Randive, Rahul Dixit and Himanshu Pandey
Thermoelectrics turn waste heat into electricity, but finding new ones requires transport calculations too costly for whole databases. Searches therefore choose what to calculate from the electronic density of states (DOS), increasingly predicted by machine learning, yet such choices are rarely tested. We test them on all 106,235 Heusler structures in the DXMag database, screening 51,257 on density-functional spectra and 54,978 on neural-network predictions, and judging both by 3,625 band-structure and transport calculations. A DOS-derived Seebeck indicator ranks most compounds passing every transport and stability test within the top 1% of their population, and ten of the eleven established half-Heusler thermoelectrics calculated pass. Predicted spectra lose most band gaps, unnoticed by spectral-similarity metrics, yet still rank passing compounds near the top. The screen certifies 80 computational candidates, 61 without reported measurements. Computed or predicted, the DOS can choose what to calculate; only a band structure shows whether a gap exists.
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Materials Science
Local-resolvent formulation and assessment of linear-scaling Kohn-Sham calculations
Albert Linda
Kohn-Sham density-functional theory is expensive because it needs orbitals that extend over the whole system. For
insulators this can be avoided by using only the diagonal of the one-electron resolvent, $g(\mathbf{r},z)=\langle\mathbf{r}|(z-\hat h)^{-1}|\mathbf{r}\rangle$, at a few complex energies $z$. We call the scheme local-resolvent density-functional theory (LRes-DFT). The density and the band energy are linear in $g$, so neither orbitals nor a kinetic-energy functional are needed. The complex energies are $M$ equally spaced points on a circle that encloses the occupied levels, offset by half a spacing so that no point lies on the real axis. Summing the resolvent over them is equivalent to occupying each level with $1/(1+u^M)$, where $u$ is the level's energy measured from the circle's center in units of its radius. This is a smooth step that is near 1 inside the circle and near 0 outside, and it stays between 0 and 1 for every $M$. If the circle moves with the chemical potential, forces at fixed electron number are exact. Gauss-Legendre and Zolotarev rules need fewer points when the gap is small. In three dimensions we use eigenpairs of small windows around each molecule instead of resolvents. This is divide-and-conquer (DC) with a different occupation function, and it is as accurate as DC with Fermi-Dirac occupations. For H$_2$ molecular
crystals of up to 1024 electrons it agrees with Kohn-Sham to $2.5\times10^{-7}$ Ha per electron. On one core it is slower than dense diagonalization below about 500 electrons and 3.5 times faster at 1024 electrons. It loses accuracy for disordered or compressed systems and for diffuse basis functions.
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Materials Science
Tellurium trioxide as an n-type wide-gap semiconductor with ultrahigh work functions from first principles
Tianwei Wang, Teruya Nagafuji, Kota Hanzawa et al. (+2 more)
The exploration of next-generation wide-gap
semiconductors with extreme work functions is highly desirable for the continued advancement of electronic and optoelectronic devices. By using first principles calculations, we show that e̱ta}-TeO3, with a wide band gap exceeding 3 eV, emerges as a promising n-type
semiconductor exhibiting ultrahigh work functions of up to ~8 eV. Intentionally or unintentionally incorporated interstitial H, Li, Na, Cu, Mg, and Zn impurities and substitutional F impurities are identified as shallow donors, whereas O vacancies act as minor carrier-compensating defects that locally trap electrons at neighbouring Te sites. The work function is evaluated across a series of low-index nonpolar surfaces. The presence of ordered O vacancies is energetically favoured on these surfaces and tends to reduce the corresponding work functions. These findings underscore the significance of precise control over the O chemical potential to suppress surface O-vacancy formation, thereby preserving the exceptional electronic performance of e̱ta}-TeO3 associated with ultrahigh work functions. Collectively, the results highlight the potential of e̱ta}-TeO3 for hole injection/extraction/transport layers as well as transparent electrodes for applications such as light-emitting devices and photovoltaic
cells, while providing useful guidance on carrier doping and surface tuning for these practical applications through elucidating the effects of the point-defect and surface configurations on the electronic properties.
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All authors Tianwei Wang, Teruya Nagafuji, Kota Hanzawa, Hidenori Hiramatsu, Fumiyasu Oba