Materials Science · Cross-listed from physics.app-ph
A Multi-Fidelity Bayesian Neural Operator for Mechanics of Spinodal Metamaterial
Pu You, Hongshun Chen, Bahador Bahmani et al. (+1 more)
Cellular metamaterials offer a vast design space for tailoring nonlinear mechanical responses, yet exploring this space with conventional modeling approaches is often infeasible or not scalable. To fully exploit their nonlinear behavior for inverse design, it is essential to learn the full stress-strain response rather than relying on bulk quantities, motivating the use of neural operators for function-to-function mapping. However, data-driven modeling of nonlinear response for metamaterials is severely constrained by the limited availability of costly experimental data. Here, we propose a
Bayesian multi-fidelity deep operator network that aggregates abundant low-fidelity finite element simulations with sparse high-fidelity experimental data from in-situ nanomechanical experiments on spinodal metamaterials, enabling heterogeneous information aggregation. A hybrid
Bayesian active learning strategy is introduced to select informative samples by jointly maximizing epistemic uncertainty and
geometric diversity of the microstructure, substantially reducing the cost of 3D nonlinear simulations. This approach adaptively trains the low-fidelity operator, which is then augmented by a high-fidelity
Bayesian residual learner. We demonstrate that only 22 strategically selected samples from a design pool of 3000 are sufficient to achieve an 84.1 percent reduction in MSE compared to the high-fidelity baseline. The framework significantly outperforms single-fidelity baselines, providing superior predictions for full nonlinear stress-strain responses as well as stiffness, strength, and energy absorption. This work provides a robust, data-efficient pathway for the inverse design and constitutive modeling of cellular metamaterials.
Read the full abstract ▾
All authors Pu You, Hongshun Chen, Bahador Bahmani, Horacio D. Espinosa
Materials Science
Temperature dependence of electronic conductivity from ab initio thermal simulation
Ridwan Hussein, Chinonso Ugwumadu, Kishor Nepal et al. (+3 more)
We present a temperature-dependent extension of the approximate electronic conductivity formula of Hindley and Mott that leverages time-averaged fluctuations of the electronic density of states obtained from ab initio molecular dynamics. By thermally averaging the square of the density of states near the
Fermi level, we obtain an estimate of the temperature dependence of the conductivity. This approach termed the thermally-averaged Hindley-Mott (TAHM) method was applied to five representative systems: crystalline aluminum (c-Al), aluminum with a grain boundary (AlGB), a four-layer
graphene-aluminum composite (Al-Gr), amorphous silicon (a-Si) and amorphous germanium-antimony-telluride (a-GST). The method reproduces the expected Bloch-Gruneisen decrease in conductivity for c-Al and AlGB. Generally, the reduction (increase) in conductivity for metallic (semiconducting) materials are reproduced. It captures microstructure-induced, thermally activated conduction in multilayer Al-Gr, a-Si and a-GST. Overall, the approach provides a computationally efficient link between time-dependent electronic structure and temperature-dependent transport, offering a simple and approximate tool for exploring electronic conductivity trends in complex and disordered materials.
Read the full abstract ▾
All authors Ridwan Hussein, Chinonso Ugwumadu, Kishor Nepal, Roxanne M. Tutchton, Keerti Kappagantula, David Alan Drabold
Materials Science
Thermodynamic assessment of machine learning models for solid-state synthesis prediction
Jane Schlesinger, Simon Hjaltason, Nathan J. Szymanski et al. (+1 more)
Machine learning models have recently emerged to predict whether hypothetical solid-state materials can be synthesized. These models aim to circumvent direct first-principles modeling of solid-state phase transformations, instead learning from large databases of successfully synthesized materials. Here, we assess the
alignment of several recently introduced synthesis prediction models with material and reaction thermodynamics, quantified by the energy with respect to the convex hull and a metric accounting for thermodynamic selectivity of enumerated synthesis reactions. A
dataset of successful synthesis recipes was used to determine the likely bounds on both quantities beyond which materials can be deemed unlikely to be synthesized. With these bounds as context, thermodynamic quantities were computed using the CHGNet foundation potential for thousands of new hypothetical materials generated using the Chemeleon generative model. Four recently published machine learning models for synthesizability prediction were applied to this same
dataset, and the resultant predictions were considered against computed thermodynamics. We find these models generally overpredict the likelihood of synthesis, but some model scores do trend with thermodynamic heuristics, assigning lower scores to materials that are less stable or do not have an available synthesis recipe that is calculated to be thermodynamically selective. In total, this work identifies existing gaps in machine learning models for materials synthesis and introduces a new approach to assess their quality in the absence of extensive negative examples (failed syntheses).
Read the full abstract ▾
All authors Jane Schlesinger, Simon Hjaltason, Nathan J. Szymanski, Christopher J. Bartel
Materials Science
Tuning Terahertz Optomechanics of MoS2 Bilayers with Homogeneous In-plane Strain
S. Patel, Jose D. Mella, S. Puri et al. (+2 more)
Homogeneous in-plane biaxial tensile strain strengthens the out-of-plane van der Waals (vdW) interaction in \MoS\
bilayers (BLs) and can be used to fine-tune their terahertz (THz) oscillations. Using ultralow-frequency Raman spectroscopy on hexagonal (2H) and rhombohedral (2R) stacked BLs, we observe a hardening of the interlayer breathing modes originating from a strain-induced Poisson contraction of the vdW separation between the layers characterized by an effective out-of-plane Poisson's ratio of $\nu_\mathrm{eff} \approx 0.19\text{--}0.24$. Strikingly, this
geometric contraction drives the system into a highly repulsive regime of the intermolecular potential, corresponding to a Grüneisen parameter of $\gamma \approx 14\text{--}20$. This value surpasses even the `
giant' one reported for phosphorene, establishing these van der Waals BLs as highly tunable nonlinear mechanical platforms that can be addressed at the THz regime without external pressure knobs.
Read the full abstract ▾
All authors S. Patel, Jose D. Mella, S. Puri, Salvador Barraza-Lopez, H. Nakamura
Materials Science
Synthesis and guided assembly of niobium trisulfide nanowires and nanowire chains by chemical vapor deposition
Thang Pham, Arindom Nag, Kate Reidy et al. (+2 more)
One-dimensional (1D) nanostructures of transition metal trichalcogenides (TMT) show unique properties through the combination of their anisotropic bonding and low dimensionality. Scalable synthesis approaches that enable control over the morphology, dimensions, and interfaces of 1D TMTs with other nanoscale materials could allow these properties to be used in novel devices. Here, we report chemical vapor deposition of a 1D TMT, namely niobium trisulfide (NbS3) in the form of nanowires, on different substrates, including bulk substrates (amorphous SiO2/Si and crystalline c-sapphire) and several two-dimensional (2D) van der Waals materials (
graphene, h-BN, CrSBr). We demonstrate high growth yield with axial growth rates of up to 40 micrometer/min and with two different growth modes: short nanowires of rectangular cross-section, and unusual long, "chained nanowires" up to 100 micrometer in length with sawtooth morphology. We discuss a mechanism that accounts for the two morphologies and discuss how the structure can be tuned through substrate choice and growth conditions. We further demonstrate guided assembly at the edges of
graphene and h-BN, as well as epitaxial growth on few-layer CrSBr and c-sapphire. These results open pathways to explore scalable synthesis and directed assembly of 1D TMT nanomaterials in unique morphologies.
Read the full abstract ▾
All authors Thang Pham, Arindom Nag, Kate Reidy, Michael A. Filler, Frances M. Ross
Materials Science
Electrically and optically active charge carrier traps in silicon-doped few-layer GaSe
M. Bissolo, R. Li, M. Ogura et al. (+9 more)
Understanding defects in atomically thin van der Waals (vdW)
semiconductors is essential for advancing their use in next-generation optoelectronic and photovoltaic devices. Here, we apply a combination of various impedance spectroscopy techniques to two-dimensional (2D) vdW GaSe doped with silicon (Si) to reconstruct deep trap states across the full bandgap. Deep-level transient spectroscopy reveals three distinct deep states 0.31, 0.88, and 1.40 eV below the conduction band edge. Complementary deep-level optical spectroscopy and photocapacitance measurements identify three deep states at 1.4 and 1.8 eV below the conduction band edge, and 2.0 eV above the valence band edge, with thermal admittance spectroscopy providing additional verification and further resolving two trap states, at 0.16 eV above the valence band edge and at 0.26 eV below the conduction band edge. By comparing the experimentally extracted ionization energies with the predictions of density functional theory, our results attribute these trap states primarily to Si-related defects and metal vacancies. This work presents a comprehensive defect map of Si-doped GaSe, providing critical insights into carrier trapping mechanisms that are essential for optimizing the design of 2D material-based devices for industrial applications.
Read the full abstract ▾
All authors M. Bissolo, R. Li, M. Ogura, Z. Sofer, S. Polesya, D. Han, A. W. Holleitner, C. Kastl, G. Koblmüller, H. Ebert, E. Zallo, J. J. Finley
Materials Science
Observation of a structurally driven, reversible topological phase transition in a distorted square net material
Xian P. Yang, Chia-Hsiu Hsu, Gokul Acharya et al. (+14 more)
Topological materials hold immense promise for exhibiting exotic
quantum phenomena, yet achieving controllable topological phase transitions remains challenging. Here, we demonstrate a structurally driven, reversible topological phase transition in the distorted square net material GdPS, induced via in situ potassium dosing. Using angle-resolved photoemission spectroscopy and first principles calculations, we demonstrate a cascade of topological phases in the sub-surface P layer: from a large, topologically trivial band gap to a gapless Dirac cone state with a 2 eV dispersion, and finally to a two-dimensional topological
insulator as inferred from theory. This
evolution is driven by subtle structural distortions in the first P layer caused by potassium adsorption, which in turn contribute to the band gap closure and topological phase transition. Furthermore, the ability to manipulate the
topology of a sub-surface layer in GdPS offers a unique route for exploring and controlling topological states in bulk materials.
Read the full abstract ▾
All authors Xian P. Yang, Chia-Hsiu Hsu, Gokul Acharya, Junyi Zhang, Md Shafayat Hossain, Tyler A. Cochran, Bimal Neupane, Zi-Jia Cheng, Santosh Karki Chhetri, Byunghoon Kim, Shiyuan Gao, Yu-Xiao Jiang, Maksim Litskevich, Jian Wang, Yuanxi Wang, Jin Hu, M. Zahid Hasan
Materials Science · Cross-listed from cond-mat.str-el
Classical Benchmarks of a Symmetry-Adapted Variational Quantum Eigensolver for Real-Time Green's Functions in Dynamical Mean-Field Theory
Aadi Singh, Chakradhar Rangi and Ka-Ming Tam
We present a variational
quantum eigensolver (VQE) approach for solving the Anderson
Impurity Model (AIM) arising in Dynamical Mean-Field Theory (DMFT). Recognizing that the minimal two-site approximation often fails to resolve essential spectral features, we investigate the efficacy of VQE for larger bath discretizations while adhering to near-term hardware constraints. We employ a
symmetry-adapted ansatz enforcing conservation of particle number $(N)$,
spin projection $(S_z=0)$, and total
spin $(S^2=0)$
symmetry, benchmarking the performance against exact diagonalization across different interaction strengths using bath parameters extracted from the DMFT self-consistency loop. For a four-site model, the relative error in the ground state energy remains well below $0.01%$ with a compact parameter set $(N_p \le 30)$. Crucially, we demonstrate that the single-particle Green's function-the central quantity for DMFT-can be accurately extracted from VQE-prepared ground states via real-time
evolution in the intermediate to strong interaction regimes. However, in the weak interaction regime, the Green's function exhibits noticeable deviations from the exact
benchmark, particularly in resolving low-energy spectral features, despite the ground state energy showing excellent agreement. These findings demonstrate that VQE combined with real-time
evolution can effectively extend
quantum-classical hybrid DMFT beyond the two-site approximation, particularly for describing insulating phases. While this approach offers a viable pathway for simulating strongly correlated materials on near-term devices, the observation that accurate ground state energy does not guarantee accurate dynamical properties highlights a key challenge for applying such approaches to correlated metals.
Read the full abstract ▾
Materials Science · Cross-listed from cond-mat.soft
Vacancy defects in square-triangle tilings and their implications for quasicrystals formed by square-shoulder particles
Alptuğ Ulugöl, Giovanni Del Monte, Eline K. Kempkes et al. (+2 more)
Almost all observed square-triangle quasicrystals in soft-matter systems contain a large number of point-like defects, yet the role these defects play in stabilizing the quasicrystal phase remains poorly understood. In this work, we investigate the thermodynamic role of such defects in the widely observed 12-fold symmetric square-triangle quasicrystal. We develop a new Monte Carlo simulation to compute the configurational
entropy of square-triangle tilings augmented to contain two types of irregular hexagons as defect tiles. We find that the introduction of defects leads to a notable
entropy gain, with each defect contributing considerably more than a conventional vacancy in a periodic
crystal. Intriguingly, the
entropy gain is not simply due to individual defect types but isamplified by their combinatorial mixing. We then apply our findings to a microscopic model of core-corona particles interacting via a square-shoulder potential. By combining the configurational
entropy with vibrational free-energy calculations, we predict the
equilibrium defect concentration and confirm that the quasicrystalline phase contains a higher concentration of point-defects than a typical periodic
crystal. These results provide a new understanding of the prominence of observed defects in soft-matter quasicrystals.
Read the full abstract ▾
All authors Alptuğ Ulugöl, Giovanni Del Monte, Eline K. Kempkes, Frank Smallenburg, Laura Filion
Materials Science
Origin of mixed anisotropy in crystalline Permalloy and amorphous Cobalt thin films individually deposited on Si substrate
Kirti Kirti, Baisali Ghadai, Abinash Mishra et al. (+2 more)
Magnetic anisotropy (MA) plays a crucial role in deciding both static and dynamic behaviour of
magnetic thin films. It controls various phenomena, such as magnetization reversal, domain formation, domain-wall motion,
spin-wave generation, and
spin-wave propagation etc. We investigate the mixed anisotropies in face-centred-cubic Permalloy (fcc-Py) and amorphous Cobalt (a-Co) thin films deposited via rf magnetron sputtering on Si (100) substrate with thicknesses, d = 5-125 nm and t = 5-150 nm, respectively. X-ray diffraction technique, atomic force microscopy, and vibrating sample magnetometry are employed to study the structural, morphological, and
magnetic properties. We adopt a qualitative approach to understand the nature of different anisotropies present in both materials. Mixed anisotropies evolve with film thicknesses for both fcc-Py and a-Co films. The role of growth conditions in the emergence of specific anisotropies is discussed in detail. An alteration of the magnetization easy axis from the conventional in-plane orientation is evidenced due to the collective influence of these mixed anisotropies. Based on the dominance of anisotropy components, their origin, and the direction of magnetization tilt, we categorize our samples as belonging to specific regimes. Introduction of magnetization tilt has been proven to be an extremely innovative way to improve the performance of spintronic devices so far. The one-to-one comparison between a sputter-deposited crystalline and an amorphous
magnetic material could be beneficial for building a stronger foundation for that.
Read the full abstract ▾
All authors Kirti Kirti, Baisali Ghadai, Abinash Mishra, Rahulkrishnan R, Sucheta Mondal
Materials Science · Cross-listed from cond-mat.stat-mech
The Mpemba effect in the Descartes protocol: A time-delayed Newton's law of cooling approach
Andrés Santos
We investigate the direct and inverse Mpemba effects within the framework of the time-delayed Newton's law of cooling by introducing and analyzing the Descartes protocol, a three-reservoir thermal scheme in which each sample undergoes a single-step quench at different times. This protocol enables a transparent separation of the roles of the delay time $\tau$, the waiting time $t_{\text{w}}$, and the normalized warm temperature $\omega$, thus providing a flexible setting to characterize anomalous thermal relaxation. For instantaneous quenches, exact conditions for the existence of the Mpemba effect are obtained as bounds on $\omega$ for given $\tau$ and $t_{\text{w}}$. Within those bounds, the effect becomes maximal at a specific value $\omega=\widetilde{\omega}(t_{\text{w}})$, and its magnitude is quantified by the extremal value of the temperature-difference function at this optimum. Accurate and compact approximations for both $\widetilde{\omega}(t_{\text{w}})$ and the maximal magnitude $\text{Mp}(t_{\text{w}})$ are derived, showing in particular that the absolute maximum at fixed $\tau$ is reached for $t_{\text{w}}=\tau$. A comparison with a previously studied two-reservoir protocol reveals that, despite its additional control parameter, the Descartes protocol yields a smaller maximal magnitude of the effect. The analysis is extended to finite-rate quenches, where strict equality of bath conditions prevents a genuine Mpemba effect, although an approximate one survives when the bath time scale is sufficiently short. The developed framework offers a unified and analytically tractable approach that can be readily applied to other multi-step thermal protocols.
Read the full abstract ▾
Materials Science
Polytype-Dependent Upconversion Photoluminescence in 3R-MoS2
Omri Meron, Idan Kizel, Dror Hershkovitz et al. (+6 more)
Ferroelectric van der Waals materials offer switchable polarization states, yet optical readout of their stacking configurations remains challenging. Here, building on the resonant
exciton-
exciton annihilation (EEA) mechanism recently identified in 2H-phase TMDs, we report the first observation of upconversion photoluminescence (UPL) in rhombohedral MoS$_2$ and demonstrate that this many-body process is strongly polytype-dependent. Using low-temperature spectroscopy, we observe anti-Stokes emission with superlinear power dependence characteristic of EEA. Beyond serving as an accurate layer-number sensor due to discrete bandgap variations, UPL provides a sensitive probe of stacking order across thicknesses. The two neutral trilayer polytypes, which remain indistinguishable by surface potential measurements and second harmonic generation, exhibit markedly different UPL intensities. This sensitivity persists in thicker samples where multiple configurations coexist. First-principles calculations suggest that the intensity contrast originates primarily from the layer confinement of the annihilating
excitons, while energy matching to the $\Gamma$ final-state
manifold provides additional intensity selectivity. Power-dependent spectroscopy further disentangles two distinct annihilation channels originating from different dark
exciton valleys, identified through their contrasting intensity scaling and opposite density-induced energy shifts. Crucially, the annihilation process doubles the energy separation of nearly degenerate dark
excitons while converting their weak emission into bright signal, providing experimental access to valley-specific responses that are obscured in direct dark-
exciton spectroscopy. Our findings demonstrate that ferroelectric configurations provide a new degree of freedom for controlling nonlinear optical processes.
Read the full abstract ▾
All authors Omri Meron, Idan Kizel, Dror Hershkovitz, Youngki Yeo, Nirmal Roy, Wei Cao, Alon Ron, Moshe Ben Shalom, Haim Suchowski
Materials Science · Cross-listed from cond-mat.soft
Ultrastable 2D glasses and packings explained by local centrosymmetry
A. Zaccone
Using the most recent numerical data by Bolton-Lum et al. [Phys. Rev. Lett. 136, 058201 (2026)], we demonstrate that ideal ultrastable glasses in the athermal limit (or ultrastable ideal 2D disk packings) possess a remarkably high degree of local centrosymmetry. In particular, we find that the inversion-
symmetry order parameter for local force transmission introduced in Milkus and Zaccone, [Phys. Rev. 93, 094204 (2016)], is as high as $F_{IS}= 0.84522$, to be compared with $F_{IS}=1$ for perfect centrosymmetric
crystals free of defects, and with $F_{IS} \sim 0.3-0.5$ for standard random packings. This observation provides a clear, natural explanation for the ultra-high shear modulus of ideal packings and ideal glasses, because the high centrosymmetry prevents non-affine relaxations which decrease the shear modulus. The same mechanism explains the absence of
boson peak-like soft vibrational modes. These results also confirm what was found previous work, i.e. that the bond-orientational order parameter is a very poor correlator for the vibrational and mechanical
Read the full abstract ▾
Materials Science · Cross-listed from physics.comp-ph
Transformation front kinetics in deformable ferromagnets
Michael Poluektov
Materials such as
magnetic shape-
memory alloys possess an intrinsic coupling between material's magnetisation and mechanical deformation. These materials also undergo structural phase transitions, with phase boundaries separating different phases. The kinetics of the phase boundaries is governed by the
magnetic field and the mechanical stresses. There is a multiplicity of other materials revealing similar phenomena, e.g.\
magnetic perovskites. To model the propagation of the phase boundaries in deformable
magnetic materials at the continuum scale, three ingredients are required: a set of governing equations for the bulk behaviour with coupled
magnetic and mechanical degrees of freedom, a dependency of the phase boundary velocity on the governing factors, and a reliable computational method. The expression for the phase boundary velocity is usually obtained within the continuum thermodynamics setting, where the
entropy production due to phase boundary propagation is derived, which gives a thermodynamic driving force for the phase boundary kinetics. For deformable ferromagnets, all three elements (bulk behaviour, interface kinetics, and computational approaches) have been explored, but under a number of limitations. The present paper focuses on the derivation of the thermodynamic driving force for transformation fronts in a general magneto-mechanical setting, adapts the cut-finite-element method for transformation fronts in magneto-mechanics, which allows for an exceptionally efficient handling of the propagating interfaces, without modifying the finite-element mesh, and applies the developments to qualitative modelling of magneto-mechanics of
magnetic shape-
memory alloys.
Read the full abstract ▾
Materials Science
Role of magnon-magnon interaction in optical excitation of coherent two-magnon modes
E.A. Arkhipova, A. E. Fedianin, I.A. Eliseyev et al. (+4 more)
Two-
magnon modes are terahertz-frequency
magnetic excitations in antiferromagnets, governed by exchange interactions, involving
magnons from the entire Brillouin zone and dominated by zone-edge
magnons. The ability to couple to light promotes two-
magnon modes as contenders for ultrafast optical manipulation of the
magnetic state, beyond conventional zone-center magnonics. While
magnon-
magnon interactions are known to critically shape the two-
magnon line in spontaneous Raman scattering spectra, their role in coherent time-domain excitations remains unexplored. We report a detailed experimental and theoretical study of the influence of
magnon-
magnon interactions on coherent two-
magnon modes in a cubic antiferromagnet excited via Impulsive Stimulated Raman scattering. We reveal the nontrivial
evolution of coherent
magnetic dynamics in the time domain and the corresponding spectrum and compare it with the spontaneous Raman scattering spectrum. By extending the
spin-correlations based theory for two-
magnon modes, we derive a unified description of their spectra in Raman Scattering and Impulsive Stimulated Raman Scattering and highlight the role of
magnon-
magnon interactions.
Read the full abstract ▾
All authors E.A. Arkhipova, A. E. Fedianin, I.A. Eliseyev, R.M. Dubrovin, P.P. Syrnikov, V.Yu. Davydov, A.M. Kalashnikova
Materials Science
Ab initio Phase Diagram of Ta2O5
Yan Gong, Huimin Tang, Yong Yang et al. (+1 more)
Tantalum pentoxide (Ta2O5) is a polymorphic wide-bandgap
semiconductor with outstanding dielectric properties and widespread use in optical and electronic technologies. Its rich structural diversity, arising from multiple polymorphs accessible under different synthesis conditions, has made Ta2O5 a long-standing subject of interest. However, a unified understanding of the thermodynamic stability and phase transitions of its polymorphs across pressure-temperature (P-T) space has remained elusive. Here, using first-principles calculations, we map the thermodynamic landscape of Ta2O5 and establish a comprehensive P-T phase diagram together with a phase-stability hierarchy. We find that Gamma-Ta2O5 and B-Ta2O5 dominate the phase diagram over a broad range of P-T conditions: Gamma-Ta2O5 is stabilized at low pressures, while B-Ta2O5 becomes thermodynamically favored at higher pressures up to ~ 60 GPa, beyond which Y-Ta2O5 emerges as the most stable phase. Crucially, the zero-point energy (ZPE), one aspect of
nuclear quantum effects (NQEs), plays a significant role in determining relative phase stability, contributing substantially to the Gibbs free energy and altering phase boundaries. A re-entrant phase transition between Gamma and B-Ta2O5 is predicted near ~ 2 GPa, revealing unexpected complexity in the phase behavior of this
oxide. More generally, we identify a characteristic temperature (T_0), at which zero-point and thermal
phonon contributions to the free energy become comparable, and show that T_0 is approximately one-third of the Debye temperature. This relationship provides a simple, physically transparent criterion for assessing the importance of NQEs in phase stability, with implications extending beyond Ta2O5 to a broad class of complex
oxides.
Read the full abstract ▾
All authors Yan Gong, Huimin Tang, Yong Yang, Yoshiyuki Kawazoe
Materials Science · Cross-listed from cond-mat.str-el
Evidence for Many-Body States in NiPS$_3$ Revealed by Angle-Resolved Photoelectron Spectroscopy
Miłosz Rybak, Benjamin Pestka, Biplab Bhattacharyya et al. (+11 more)
We present $\mu$-ARPES spectra of the Mott-insulating van der Waals antiferromagnet NiPS$_3$. Signatures of strong correlations – such as the onset of atomic or atomic-ligand multiplets and
spin-orbit-entangled
exciton have been observed in this material by various two-particle spectroscopies, but not previously in photoemission. Our measurements reveal a weakly dispersive feature at the valence-band edge that is absent in DFT+$U$ calculations and remains unchanged across the Néel transition. After critically examining and ruling out alternative interpretations, we show that an exact diagonalization of a NiS$_6$ cluster yields low-energy final-state configurations of mixed multiplet $d^7$ and $d^8\underline{L}$ character, whose energy differences are consistent with the observed additional feature. This implies that ARPES directly accesses local Ni-S multiplet physics in NiPS$_3$, revealing a many-body structure beyond mean-field theory. Our results confirm that NiPS$_3$ is an excellent model platform in which strong correlations, reduced dimensionality, and covalent metal-ligand bonding jointly shape both two- and single-particle spectroscopies, underscoring the need for a genuinely
quantum many-body description of two-dimensional
quantum materials.
Read the full abstract ▾
All authors Miłosz Rybak, Benjamin Pestka, Biplab Bhattacharyya, Jeff Strasdas, Adam K. Budniak, Adi Harchol, Vitaliy Feyer, Iulia Cojocariu, Daniel Baranowski, Yaron Amouyal, Efrat Lifshitz, Markus Morgenstern, Magdalena Birowska, Krzysztof Wohlfeld
Materials Science · Cross-listed from physics.geo-ph
Radial gradient of superionic hydrogen in Earth's inner core
Zepeng Wu, Liangrui Wei, Chen Gao et al. (+3 more)
Hydrogen is considered a key light element in Earth's core, yet the thermodynamics of its superionic phase and its distribution in the inner core remain unclear. Here, we compute ab initio Gibbs free energies for
liquid and superionic hcp and bcc Fe-H phases and construct the superionic-
liquid phase diagram over pressure-temperature conditions relevant to the Earth's inner core. We find that phase diagrams at different inner-core pressures collapse when temperatures are scaled by the melting temperature of pure iron, indicating that solid-
liquid partitioning is controlled primarily by a reduced temperature relative to iron melting and is weakly sensitive to pressure. This scaling relation further reconciles previously reported discrepancies in partition coefficients among theoretical studies and yields good agreement with available experimental data at low pressures. By applying thermochemical constraints, our free-energy results reveal a radial hydrogen gradient within the inner core. These results demonstrate that compositional gradients of superionic hydrogen in the inner core emerge naturally from
equilibrium thermodynamics and suggest a general mechanism governing the depth-dependent distribution of light elements within Earth's inner core.
Read the full abstract ▾
All authors Zepeng Wu, Liangrui Wei, Chen Gao, Shunqing Wu, Renata M. Wentzcovitch, Yang Sun
Materials Science
Skyrmions in 2D chiral magnets with noncollinear ground states stabilized by higher-order interactions
Mathews Benny, Moinak Ghosh, Moritz A. Goerzen et al. (+4 more)
Magnetic skyrmions are intriguing topological
spin textures that have attracted great
attention due to their potential for future spintronic devices. Skyrmions have so far been explored in different
magnetic materials, such as ferromagnets, antiferromagnets, and ferrimagnets. Here, we propose a new type of unconventional skyrmions stabilized in noncollinear magnets. Using first-principles calculations and atomistic
spin simulations, we demonstrate that a noncollinear ground state can be stabilized in Rh/Co and Pd/Co atomic
bilayers on the Re(0001) surface by four
spin exchange interactions, although Co – a material often used in applications – is a prototypical ferromagnet with strong pairwise exchange interaction. We further show that unconventional skyrmion
lattices and isolated skyrmions can emerge on this noncollinear
magnetic background. Transition-state theory calculations reveal that these metastable skyrmions are protected by large energy barriers, suggesting that they could be observed in experiments. These unconventional types of skyrmions in noncollinear magnets might open new possibilities for topological
spin transport or magnet-
superconductor hybrid systems.
Read the full abstract ▾
All authors Mathews Benny, Moinak Ghosh, Moritz A. Goerzen, Bjarne Beyer, Hendrik Schrautzer, Stefan Heinze, Souvik Paul
Materials Science
Emergent 3D Fermiology and Magnetism in an Intercalated Van der Waals System
Luigi Camerano, Emanuel A. Martínez, Victor Porée et al. (+16 more)
Intercalation of
magnetic atoms into van der Waals materials provides a versatile platform for tailoring unconventional
magnetic properties. However, its impact on electronic dimensionality and exchange mechanisms remains poorly understood. Using Fe-intercalated TaS$_2$ as a model system, we combine X-ray absorption and resonant inelastic scattering with angle-resolved photoemission and first-principles calculations to reveal that intercalation reshapes the host electronic structure. We identify a
spin-polarized intercalant-host hybridized band with pronounced out-of-plane dispersion crossing the
Fermi level, providing an itinerant channel for interlayer
magnetic exchange. This mechanism explains the breakdown of a purely atomic picture and establishes a direct link between
lattice geometry, electronic dispersion, and
magnetic order. Our findings demonstrate that intercalant-induced itinerancy enables tunable interlayer coupling in otherwise layered magnets, offering a general microscopic framework for engineering
magnetic dimensionality in a broad class of intercalated vdW materials.
Read the full abstract ▾
All authors Luigi Camerano, Emanuel A. Martínez, Victor Porée, Laura Martella, Dario Mastrippolito, Debora Pierucci, Franco D'Orazio, Polina M. Sheverdyaeva, Paolo Moras, Enrico Della Valle, Tianlun Yu, Moritz Hoesch, Craig M. Polley, Thiagarajan Balasubramanian, Alessandro Nicolaou, Luca Ottaviano, Vladimir N. Strocov, Gianni Profeta, Federico Bisti
Materials Science
Acceleration of Atomistic NEGF: Algorithms, Parallelization, and Machine Learning
Mathieu Luisier, Nicolas Vetsch, Alexander Maeder et al. (+8 more)
The Non-
equilibrium Green's function (NEGF) formalism is a particularly powerful method to simulate the
quantum transport properties of nanoscale devices such as transistors, photo-diodes, or
memory cells, in the ballistic limit of transport or in the presence of various scattering sources such as electronphonon, electron-
photon, or even electron-electron interactions. The inclusion of all these mechanisms has been first demonstrated in small systems, composed of a few atoms, before being scaled up to larger structures made of thousands of atoms. Also, the accuracy of the models has kept improving, from empirical to fully ab-initio ones, e.g., density functional theory (DFT). This paper summarizes key (algorithmic) achievements that have allowed us to bring DFT+NEGF simulations closer to the dimensions and functionality of realistic systems. The possibility of leveraging graph neural networks and machine learning to speed up ab-initio device simulations is discussed as well.
Read the full abstract ▾
All authors Mathieu Luisier, Nicolas Vetsch, Alexander Maeder, Vincent Maillou, Anders Winka, Leonard Deuschle, Chen Hao Xia, Manasa Kaniselvan, Marko Mladenovic, Jiang Cao, Alexandros Nikolaos Ziogas
Materials Science
Single-Atom Adsorption on h-BN along the Periodic Table of Elements: From Pristine Surface to Vacancy-Engineered Sites
Ana S. Dobrota, Natalia V. Skorodumova and Igor A. Pašti
The adsorption of single atoms on pristine and defected hexagonal boron nitride (h-BN) was systematically investigated using density functional theory. Elements from the first three rows of the periodic table, together with selected transition and coinage metals, were examined on the pristine surface and at boron- and nitrogen-vacancy sites. On pristine h-BN, adsorption is generally weak and dominated by dispersion forces, with measurable chemisorption limited to highly electronegative atoms such as C, O, and F. The introduction of vacancies transforms h-BN into a chemically active material, increasing adsorption energies by one to two orders of magnitude. The boron vacancy strongly stabilizes metallic and electropositive species through coordination to undercoordinated nitrogen atoms, whereas the nitrogen vacancy selectively binds electronegative and covalent adsorbates. Scaling of adsorption energies with elemental cohesive energies distinguishes regimes of physisorption, chemisorption, and substitutional stabilization. These insights provide a unified description of adsorption trends across the periodic table and establish defect engineering as an effective strategy for tailoring the catalytic, sensing, and electronic properties of h-BN.
Read the full abstract ▾
Materials Science
Accelerating Complex Materials Discovery with Universal Machine-Learning Potential-Driven Structure Prediction
Yuqi An and Zhenbin Wang
Universal machine-learning interatomic potentials (uMLIPs) have become powerful tools for accelerating computational materials discovery by replacing expensive first-principles calculations in
crystal structure prediction (CSP). However, their effectiveness in identifying new, complex materials remains uncertain. Here, we systematically assess the capability of a uMLIP (i.e.,M3GNet) to accelerate CSP in quaternary
oxides. Through extensive exploration of the Sr-Li-Al-O and Ba-Y-Al-O systems, we show that uMLIP can rediscover experimentally known materials absent from its training set and identify seven new thermodynamically and dynamically stable compounds. These include a new polymorph of Sr2LiAlO4 (P3221) and a new disordered phase, Sr2Li4Al2O7 (P1_bar). Furthermore, our results show stability predictions based on the semilocal PBE functional require cross-validation with higher-level methods, such as SCAN and RPA, to ensure reliability. While uMLIPs substantially reduce the computational cost of CSP, the primary bottleneck has shifted to the efficiency of search
algorithms in navigating complex structural spaces. This work highlights both the promise and current limitations of uMLIP-driven CSP in the discovery of new materials.
Read the full abstract ▾