Materials Science · Cross-listed from cond-mat.mes-hall
Landau quantization of $C_3$ high-fold fermions in honeycomb lattices
Luisa Madail and Joaquín Fernández-Rossier
We present the theory of the Landau levels of $C_3$ high-fold
fermions in honeycomb
lattices. These
fermions arise as a generalization of the tight-binding model in a honeycomb
lattice with one orbital per site, known to describe
graphene, to a family of models with several orbitals per site transforming according to representations of $C_3$, relevant for triangulene two-dimensional
crystals. The models are defined by the number of orbitals $n_a$ and $n_b$ at the $a$ and $b$ sites of the unit
cell. They feature energy bands that combine flat bands and Dirac cones, that are isomorphic to those of
graphene, the Lieb, $p_{xy}$ honeycomb, and the Kagome tight-binding models. Combining tight-binding and $k\cdot p$ methods, here we compute the Landau levels of the $(1,1)$, $(1,2)$, $(2,2)$ and $(3,3)$ models, we compare them to those of the reference models, and we explore the similarities and differences with the Landau levels in
graphene. Our findings reveal that the nature of $C_3$ high-fold
fermions combine Dirac-type Landau quantization, originating from the linear crossings and associated relativistic band dispersion, with anomalous Landau quantization rooted in the
quantum geometry of the singular flat bands.
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Materials Science
Exchange Interactions and Magnon Spectra in bcc Fe(001) Thin Films: A Computational Study
Joanna Marciniak, Wojciech Marciniak, Jorge Luis Briseño-Gómez et al. (+1 more)
We combined density functional theory with atomistic
spin dynamics to understand how surfaces influence
magnon dispersion. For this purpose, we investigate thin layers of body-centered cubic iron and compare them with the bulk material. We present how the broken
symmetry affects exchange interactions and
magnon behavior. Our results reveal enhanced
magnetic moments and exchange interactions for surface atoms compared to bulk Fe. The increase in exchange interaction integrals is mostly visible for first- and second-nearest neighbors. We also find a significant spread in exchange values within each coordination shell.
Magnon dispersion analysis shows, for the layered system, pronounced band blurring, a significant reduction of maximum frequencies relative to the previously reported bulk values, and the emergence of a low-frequency band outside the \g{}-point. Our study shows that relying on bulk exchange parameters introduces errors in the
magnon spectra of ultrathin systems, underscoring the need for a detailed, system-specific approach.
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All authors Joanna Marciniak, Wojciech Marciniak, Jorge Luis Briseño-Gómez, Jan Rusz
Materials Science
Growth-induced trade-off between polarity, electrical isolation, and structural quality in AlN grown on Si(111) by plasma-assisted molecular beam epitaxy
Hossein Yazdani, Nhu Tran, Xin Du et al. (+3 more)
We investigate the effects of substrate temperature and Al flux, at a fixed N flux, on the polarity, electrical properties, and structural quality of AlN films grown on high-resistivity Si(111) by
plasma-assisted molecular beam epitaxy. N-rich conditions result in relatively highly resistive Al-polar AlN/Si, whereas Al-rich conditions promote N-polarity and improved structural quality but simultaneously lead to increased p-type conductivity of AlN/Si stacks, consistent with unintentional Al doping of the Si substrate during AlN growth. Increasing the substrate temperature further improves the structural quality while enhancing the unwanted conductivity, revealing a growth-induced trade-off among polarity, electrical isolation, and structural quality. By reducing the substrate temperature to 575{\deg}C while maintaining slightly Al-rich conditions, an N-polar AlN/Si stack with a sheet resistance of 276 k{\Omega}/sq is achieved. These results provide guidelines for optimizing AlN/Si templates for various nitride device
heterostructures.
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All authors Hossein Yazdani, Nhu Tran, Xin Du, Vit Hornik, Roman Gröger, YongJin Cho
Materials Science
Structural identification in general crystalline systems via Voronoi cell topology
Emanuel A. Lazar and Chris H. Rycroft
Widely used methods for identifying
crystal structure in atomistic simulations are limited in practice to a handful of simple structures, leaving many important crystalline systems without automated classification techniques. Voronoi
topology analysis offers a route to classifying arbitrary crystalline and defect environments, but realizing this potential first requires enumerating the Voronoi
cell topologies that can arise under thermal perturbation of a structure of interest. We present an
algorithm that deterministically enumerates all Voronoi
cell topologies arising from generic infinitesimal perturbations of an arbitrary
crystal structure, producing structural classifiers that extend automated identification to general crystalline systems. We demonstrate the approach on several structures of general interest.
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Materials Science
Modeling electrodeposition of thin films with compact, dendritic, and random morphologies
Fábio D. A. Aarão Reis, Dung di Caprio, Sidiney G. Alves et al. (+1 more)
We summarize previously published computer simulation studies of a metal electrodeposition model that considers diffusive cation flux, a fast reaction in contact with the electrode or with the growing deposit, and adsorbed atom
diffusion in finite time windows. Simulations with various parameters show compact, fractal, dendritic deposits, and dynamic transitions between different morphologies during the growth of individual samples. The dendritic shapes are characterized by hierarchical organizations in which branches of a given order reproduce the shape and crystalline orientation of the branches of the previous order, in contrast to the random branching of the fractal deposits formed by DLA and related models. The simulations show dendrites with maple leaf shape in SC
lattices, pine tree shape in FCC
lattices, and flower-like shape in HCP
lattices, with surfaces predominantly oriented in the lowest-energy configurations of each
lattice. Simulations with nucleation restricted to a nanoscale seed show the initial formation of faceted particles followed by dendrite formation, in agreement with silver electrodeposition on substrates patterned with gold nanoparticles. A quantitative application to faceted and dendritic silver obtained in the same experiment provides values of the model parameters which are consistent with the characteristic widths of these structures being of the same order of magnitude of the
diffusion lengths of atoms on (111) and (001) surfaces. Using an extended model for iron electrodeposition on Si(100), the simulations qualitatively reproduce the initial formation of multilayer islands, small oscillations of the roughness of a polycrystalline compact film after island coalescence, and instability development. Possible directions for applying this modeling to the electrodeposition of other materials are suggested.
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All authors Fábio D. A. Aarão Reis, Dung di Caprio, Sidiney G. Alves, Ismael S. S. Carrasco
Materials Science · Cross-listed from cond-mat.supr-con
Bulk superconductivity in quintuple-layer square-planar nickelate La6Ni5O12
Mengzhu Shi, Mei Du, Hongyu Li et al. (+5 more)
Nickelate
superconductors, sharing a similar electronic environment with cuprate
superconductors, offer a promising platform for unraveling the mechanism of high-temperature superconductivity. However, the realization of superconductivity in these systems has so far been restricted to thin films or bulk samples under high-pressure. This limits the applicability of various experimental probes to study the mechanism of superconductivity, and hinders the potential application of the nickelate
superconductors. Exploring bulk superconductivity at ambient pressure is therefore essential to understand its origin and enable broader experimental research. Here, we report the realization of bulk superconductivity at ambient-pressure in quintuple-layer square-planar (SP) nickelate La6Ni5O12. The SP phase is obtained by performing topotactic reaction on the quintuple-layer Ruddlesden-Popper (RP) compound La6Ni5O16. Optimized reduction condition endows La6Ni5O12 with a superconducting state that exhibits onset transition temperature of ~ 18 K, as verified by both zero resistance and diamagnetic shielding effect. Pronounced hysteresis loops revealed by magnetization and torque magnetometry demonstrate the occurrence of
vortex pinning. Specific heat measurements on a polycrystalline pellet of La6Ni5O12 reveal a clear superconducting transition at ~18 K and a superconducting volume fraction of ~ 25%, which strongly supports the presence of bulk superconductivity. Our results establish an unprecedented bulk sample platform for investigating superconductivity in nickelates at ambient pressure, which paves the way for further experimental studies into the superconducting mechanism.
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All authors Mengzhu Shi, Mei Du, Hongyu Li, Zhiwei Wang, Zhengjie Wang, Ziji Xiang, Tao Wu, Xianhui Chen
Materials Science
A Topological\-Geometrical Descriptor (TGD) for Scalable and Interpretable Modeling of Two\-Dimensional Carbon Networks
Rômulo Uriel Liberal de Oliveira and Raphael Matozo Tromer
We introduce a compact Topological-Geometrical Descriptor (TGD) for planar two-dimensional carbon networks. Atomic coordinates are mapped to a periodic planar graph and represented through ring populations, topological-charge statistics, projected ring geometry, and dual-graph defect adjacency. The resulting modeling vector contains 19 physically interpretable features. We evaluate TGD on 120 published planar carbon allotropes using the DFT relative energy per atom with respect to
graphene as the target. Repeated five-fold cross-validation with gradient boosting yields a mean absolute error (MAE) of 0.0826 +/- 0.0138 eV/atom and R2 = 0.803 +/- 0.074. Under the same validation protocol, TGD gives a mean MAE of 0.0828 eV/atom, compared with 0.0929 eV/atom for a 203-feature Matminer representation. We further analyze 360 vacancy-defected
graphene configurations spanning 12 vacancy concentrations from 2 to 24 percent. When entire vacancy concentrations are held out, TGD gives a pooled MAE of 0.269 eV/vacancy and R2 = 0.861, outperforming simple baselines based on vacancy concentration alone or non-hexagonal-ring fraction alone. Sensitivity tests show that the inferred edge sets are stable to moderate changes in the adaptive bond factor. Finally, the mean absolute topological charge is examined as a one-variable empirical surrogate for the allotrope
dataset and is treated explicitly as
dataset-specific rather than universal. These results show that TGD combines compact prediction with direct structural interpretation while making clear the present restriction to single-layer planar carbon networks.
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Materials Science
High-Frequency Mass Transfer Enabling Over-Limiting Currents in Porous Electrodes
Md Abdul Hamid and Kyle C. Smith
Classical film theory predicts a finite
diffusion-limited current at porous electrodes. However, over-limiting currents (OLCs), which exceed this limit, are often observed and have been attributed to surface charge, confinement, or electrokinetic effects. Here, we use a frequency-domain framework to identify a different mechanism governed by the time scale of concentration variation. For perfectly reactive interfaces, the spectral Sherwood number, a frequency-dependent dimensionless measure of interfacial mass transfer relative to molecular
diffusion, grows as $\Shnd\sim\omega^{1/2}$ at high frequency, while its phase approaches $\pi/4$. This response corresponds to the semi-infinite Warburg limit of the electrochemical impedance. A scaling analysis shows that the exponent and prefactor are determined by
diffusion within a thin layer adjacent to the interface and are therefore independent of the global pore geometry. Numerical results for parallel plates, circular tubes, and twelve porous microstructures confirm this scaling. Geometry, flow strength, and flow direction affect the low-frequency response and crossover frequency, but not the asymptotic scaling in the high-frequency limit. This temporal route to OLCs requires neither surface charge nor confinement and could inform the design of systems for pulsed electrodeposition, mineral recovery and renewable-energy storage.
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Materials Science
Access Rate-Dependent Endurance Behavior of Ferroelectric Hafnium Zirconium Oxide Capacitors
Roberto Guido, Julie Laguerre, Pramoda Vishnumurthy et al. (+6 more)
Fluorite-structured ferroelectrics, such as hafnium zirconium oxide ($Hf_{1-x}Zr_{x}O_{2}$), are among the most promising materials for developing the next generation of low-power nonvolatile
memories. Emulating realistic operating scenarios for ferroelectric
memories requires performing access rate-dependent endurance tests. The access rate-dependent reduction of the switched polarization cannot be described as a mere superposition of fatigue and imprint effects, which are observed in conventional endurance and retention tests, respectively. The interplay between these degradation mechanisms and its correlation with the delay time in between the programming pulses remains unclear. Combining electrical testing through voltage pulses with ab initio and drift-
diffusion simulations provides a comprehensive perspective on the microscopic origin of the access rate-dependent reduction of the switched polarization of ferroelectric capacitors based on product-relevant 5 nm thick $Hf_{0.5}Zr_{0.5}O_{2}$ films. The role of oxygen vacancy defects accumulating at the electrode-ferroelectric interface with delay time in reducing the fraction of switchable domains is elucidated considering electron transfer processes which change the defect charge state. Building upon this theoretical understanding, a physics-based model to extrapolate the long-term access rate-dependent endurance performance is developed and experimentally verified for temperatures up to 135{\deg}C and delay times up to 2 ms.
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All authors Roberto Guido, Julie Laguerre, Pramoda Vishnumurthy, Florian Wunderwald, Kristina Holsgrove, Thomas Mikolajick, Sou-Chi Chang, Alfred Kersch, Uwe Schroeder
Materials Science
Identification of carbon-related color centers in hBN by high-resolution ab initio photoluminescence modeling
Vytautas Žalandauskas, Marek Maciaszek, Marianne Etzelmüller Bathen et al. (+3 more)
Identification of optically active defects in hexagonal boron nitride (hBN) remains challenging because different defect candidates can produce similar calculated photoluminescence (PL) lineshapes. Here, we demonstrate that force-constant
embedding methodology can be extended to calculate high-resolution, vibrationally resolved PL lineshapes in the polar layered material hBN. Benchmarking against the carbon dimer defect, responsible for the 4.1 eV emission, we show that the methodology accurately reproduces the low-energy acoustic
phonons and fine spectral features that are inaccessible when using direct supercell calculations. Applying the methodology to neutral carbon trimers ($\mathrm{C_2 C_B}$ and $\mathrm{C_2 C_N}$), we find that the calculated PL lineshape and excitation energy of $\mathrm{C_2 C_N}$ closely match the low-temperature spectrum of the emitter with a zero-
phonon line at 1.54 eV. These results establish high-resolution
phonon-sideband modeling as a powerful tool for discriminating among candidate defects in polar materials.
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All authors Vytautas Žalandauskas, Marek Maciaszek, Marianne Etzelmüller Bathen, Julius Janušonis, Tadas Paulauskas, Lukas Razinkovas
Materials Science · Cross-listed from physics.optics
Polaritonic self-hybridized critical coupling by Brillouin zone folding induced quasi-bound states in the continuum in bulk WS2 metasurfaces
Kuidong Wang, Xiongwei Guo, Fu Liu et al. (+2 more)
Maximizing the absorption of
exciton-polaritons in transition-metal dichalcogenides (TMDCs) under critical coupling conditions is crucial for developing high-efficiency polariton-based photodetectors, solar
cells, and perfect absorbers. Here, we propose a polaritonic critical self-hybridized coupling between Brillouin zone folding driven quasi-bound states in the continuum (BZF-QBIC) mode and A
excitons in a bulk WS2 metasurface. This polaritonic critical coupling shows robust behavior with respect to the asymmetric parameters of the involved BZF-QBIC mode, in contrast to the asymmetry-sensitive conventional QBIC-based critical coupling. By changing the height of WS2 metasurfaces, we observe a typical anti-crossing behavior with a Rabi splitting of 246.5 meV. Moreover, the maximum absorption value of 0.5 for
exciton-polaritons is achieved at the polaritonic critical coupling condition. The large population of
excitons provided by bulk WS2 is essential for achieving polaritonic critical coupling and can further enhance polaritonic absorption. This work enables the realization of robust, high-absorption self-hybridized polaritonic critical coupling in TMDCs, and further expedite their applications in high-absorption low-dimensional polaritonic devices.
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All authors Kuidong Wang, Xiongwei Guo, Fu Liu, Jinhai Si, Xun Hou
Materials Science
Sorption Molecular Dynamics of Point Defects in 2D Materials with a Machine Learning Potential
Nils-Ruben Skogemyr, Albin Sjöstedt, Isak Wernroth et al. (+6 more)
Defect engineering is a crucial tool for tuning and tailoring the properties of two-dimensional (2D) materials. A key challenge is identifying which defects are kinetically stable at room temperature and sufficiently promising to warrant further investigation. However, identifying stable defects with suitable properties using first-principles calculations, such as density functional theory (DFT) is computationally demanding, effectively limiting the scope of high-throughput studies. In this work, we investigate whether the machine learning interatomic potential MACE can reproduce sorption trends (adsorption vs. absorption) previously obtained from high-throughput DFT calculations and extend the analysis to elevated temperatures. A total of 17,624 defect structures from the ADAQ database are simulated using MACE-accelerated molecular dynamics (MD) at both 0 K and 300 K. The results show that MACE successfully reproduces the overall sorption trends observed in DFT calculations at 0 K at a fraction of the computational cost. Simulations performed at 300 K further indicate that the qualitative sorption trends remain largely the same when including finite-temperature effects. These findings demonstrate that MACE-driven MD can be used as an effective high-throughput prescreening tool for defect-related studies in 2D materials, specially related to sorption. While conventional first-principles methods, such as DFT, remain necessary for accurate and quantitative validation, the use of MLIPs enables MD simulations of finite-temperature defect behavior at a fraction of the computational cost of DFT-based MD.
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All authors Nils-Ruben Skogemyr, Albin Sjöstedt, Isak Wernroth, Isak Häggqvist, Isac Ljungwald, Hans-Ove Åkesson, Henricus R.A. ten Eikelder, Rickard Armiento, Joel Davidsson
Materials Science
Transverse magneto-gyrotropy driven by spin-induced ferroaxiality
Yoshihiro Okamura, Takumi Kagawa, Ayano Nakamura et al. (+5 more)
Photon chirality is inherently sensitive to structural handedness and magnetism, which break spatial inversion and time-reversal
symmetries, respectively. Ferroaxial order, by contrast, hosts two-dimensional chirality while preserving both
symmetries, thereby precluding its direct coupling to
photon chirality. Intertwining ferroaxiality with
magnetic order, however, may lift such constraints and enable unconventional coupling to
photon chirality. Nevertheless, the optical response arising from such intertwined order has yet to be demonstrated experimentally. Here, we demonstrate transverse magneto-gyrotropy arising from
spin-driven ferroaxiality in the Weyl magnet EuCd2Sb2. Whereas the conventional polar magneto-optical Kerr effect is governed by magnetization parallel to the light-propagation direction, we observe a gyrotropic response associated with magnetization transverse to the light-propagation direction. The optical rotation exhibits a characteristic 120-degree periodicity upon rotation of the in-plane
magnetic field, reflecting the threefold
symmetry of the emergent ferroaxial state and revealing the ferroaxial origin of the transverse gyrotropic response. This coupling to
photon chirality enables vectorial control of the gyrotropic response through the
magnetic field direction. Our findings establish an interaction between
photon chirality and transverse magnetization enabled by intertwined ferroaxial and
magnetic orders, demonstrating a novel form of multiferroicity with functional light-matter interaction.
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All authors Yoshihiro Okamura, Takumi Kagawa, Ayano Nakamura, Shinichi Nishihaya, Masaki Uchida, Susumu Minami, Ryotaro Arita, Youtarou Takahashi
Materials Science · Cross-listed from physics.chem-ph
High-Harmonic Generation Probes Quantum Nuclear Fluctuations in Liquid Water
George Trenins, Nicolas Tancogne-Dejean, Angana Mondal et al. (+5 more)
Nuclear
quantum effects are essential for an accurate description of the hydrogen-bonded structure of
liquid water, yet their spectroscopic signatures can be subtle and difficult to measure. Moreover, probing these effects in solution on femtosecond timescales (or below) is an open challenge that is pivotal for optical control of hydrogen bonds and ultrafast spectroscopy of
proton transfer. Here, we combine path-integral molecular dynamics with real-time time-dependent density-functional theory to explore high-harmonic generation (HHG) in
liquid water from first principles, rigorously accounting for
quantum nuclear delocalisation. Relative to classical-
nuclei simulations,
quantum sampling suppresses the harmonic yield around certain harmonics by up to an order of magnitude, inducing local structural minima. By analysing the ab initio simulations and reproducing the key effects with a simplified model
Hamiltonian, we trace the physical origins of the interference minima to the broadening of valence-band states induced by hydrogen-bond fluctuations, a mechanism expected to generalise to other hydrogen-bonded structures. Our work shows that nuclear
quantum effects are indispensable for capturing ultrafast electronic dynamics in
liquids, and demonstrates the power of
liquid HHG spectroscopy for attosecond probing of nuclear fluctuations.
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All authors George Trenins, Nicolas Tancogne-Dejean, Angana Mondal, Angel Rubio, Hans Jakob Wörner, Aaron Kelly, Ofer Neufeld, Mariana Rossi
Materials Science · Cross-listed from cs.LG
Beyond DFT electronic band structures via dual-space orbital learning
Minhyuk Kang, Beom Seok Kang, Nikolai Argatoff et al. (+4 more)
Accurate electronic band structures are essential for predicting material properties, but high-fidelity calculations are computationally demanding. We introduce O-kRystal, a dual-space orbital-learning framework that uses a lower-cost Perdew-Burke-Ernzerhof (PBE) calculation as both an energy baseline and a source of structured orbital information. Combining PBE band energies with real- and reciprocal-space orbital
matrices, O-kRystal predicts higher-level corrections for individual electronic states as a function of
crystal momentum and
spin. For states within 5 eV of the band-edge midpoint, it predicts Heyd-Scuseria-Ernzerhof (HSE06) band energies with a mean absolute error of $0.171 \pm 0.009$ eV across nearly 6,000 three-dimensional materials spanning insulating, metallic,
magnetic, and nonmagnetic systems. On a separate
benchmark of six strongly correlated materials, it reduces the corresponding PBE band-energy MAE by 68.7% and resolves orbital-dependent changes in the relative placement of transition-metal d and ligand p states. Despite training only at high-
symmetry points, it maintains comparable accuracy at unseen points along band paths and reconstructs HSE06 densities of states from dense Brillouin-zone predictions. Finally, training O-kRystal on $G_0W_0$ quasiparticle energies for two-dimensional materials demonstrates its applicability across levels of theory and the potential of orbital learning for higher-fidelity, momentum-resolved electronic-structure prediction beyond density functional theory.
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All authors Minhyuk Kang, Beom Seok Kang, Nikolai Argatoff, Miguel Nouman, Danish Khan, William A. Goddard III, Anima Anandkumar
Materials Science · Cross-listed from cond-mat.supr-con
Andreev-reflection spectroscopy of SrPt3P single crystals
Valeriy A. Stepanov, Nikolai D. Zhigadlo, Erik Piatti et al. (+1 more)
The interplay between inversion
symmetry breaking and superconducting pairing mechanisms is a long-standing puzzle of solid-state physics. Ternary platinum phosphide SrPt$_3$P is an excellent case study in this regard, since it shares the distorted anti-perovskite
crystal structure of non-centrosymmetric
superconductor CePt$_3$Si but preserves the inversion
symmetry center, enabling a direct comparison between the two compounds. Despite intense scrutiny, the superconducting pairing strength, gap
symmetry, and magnitude of SrPt$_3$P remain an open question. Here, we study the gap structure of high-quality SrPt$_3$P single
crystals with $T_c = 8.6$ K by using point-contact Andreev-reflection spectroscopy. The spectra systematically showed symmetric conductance maxima and a zero-bias minimum, as is typical of fully gapped
superconductors, and dips at finite voltage $V_\mathrm{dip}$ due to the local transition of the contact region to the resistive state. In contacts with high resistance, where the dips fall sufficiently far from the gap features, the conductance curves can be well fitted with a single isotropic $s$-wave gap. The temperature dependence $\Delta(T)$ of the gap amplitude extracted from the fit is in good agreement with the one predicted by the BCS theory, with a zero-temperature mean value $\Delta(0)=1.88\pm0.08$ meV, and a mean gap ratio $2\Delta/k_\mathrm{B}T_c = 5.2\pm0.2$.
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All authors Valeriy A. Stepanov, Nikolai D. Zhigadlo, Erik Piatti, Dario Daghero
Materials Science
A practical route to amorphous solid-state electrolyte structures by hybrid reverse Monte Carlo with foundation potentials
Xintian Wang, Xinyu Zhang, Denys Butenko et al. (+3 more)
Amorphous alkali oxychlorides are fast ion conductors, but their atomic structure remains unresolved. Total scattering sums all partial pair correlations into one curve that has no unique inversion, so the structure must be modeled. Melt-quench molecular dynamics builds a model from the interatomic potential alone, and reverse Monte Carlo (RMC) builds one from the measurement alone. The two have rarely been compared with all else held fixed. We
benchmark both routes and two hybrid schemes on amorphous \ce{Li_{0.9}NbO_{0.9}Cl_{4.1}} against one
neutron pair distribution function with one foundation potential. The hybrid schemes put the energy either in the acceptance rule (inline) or in short relaxations between blocks of refinement (alternating). Each refinement starts from a melt-quench glass or from a random packing of isolated units. The glass has the lowest energy and places the first-shell peaks correctly, but carries almost none of the oscillation beyond 6~Å (goodness of fit $R^{2} = 0.29$). Pure RMC fits the measurement to within its counting noise ($R^{2} = 0.99$), but at more than $1.3$~eV/atom above the glass, and niobium loses about half of its first-shell chlorine. Started from the glass, both hybrid schemes reach $R^{2} = 0.92$ within $0.1$~eV/atom of its energy and keep its coordination chemistry. Structures from the two inputs fit almost equally well and differ in energy by a tenth of the RMC penalty, yet they differ in whether their polyhedra are connected. The input is therefore part of the method. We recommend quenching a glass with a foundation potential and refining it against the measurement with a hybrid scheme. The resulting structure carries both the local chemistry and the medium-range order, and it is the starting point for modeling ion transport in these conductors.
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All authors Xintian Wang, Xinyu Zhang, Denys Butenko, Bolong Hong, Jinlong Zhu, Peichen Zhong
Materials Science
Nonadiabatic polaron dynamics from machine-learned hopping trajectories
Daniela Mangano, Luca Leoni, Zhongfei Xu et al. (+2 more)
The formation and motion of small polarons are ubiquitous in energy materials and influence photoinduced processes. Polaron transport is governed by thermally activated
lattice dynamics and rare hopping events, requiring spatial and temporal scales only attainable with machine-learning molecular dynamics, which enables extensive sampling of atomic trajectories and polaron configurations over nanoseconds. Moreover, the Born-Oppenheimer approximation underlying standard ab initio molecular dynamics cannot describe the nonadiabatic coupling between electronic states mediated by nuclear motion, which controls energy exchange and excited-state relaxation. Here, we develop a simulation framework that combines machine-learning-assisted polaron dynamics with nonadiabatic molecular dynamics to bridge these complementary aspects of polaron physics, and determine how different polaron-hopping mechanisms affect excited-state dynamics. The enlarged trajectory space allows us to provide the first direct dynamical confirmation of the adiabatic or nonadiabatic classification of polaron hopping regimes originally proposed on the basis of static Marcus-theory arguments, and to connect individual hopping events directly to nonadiabatic electronic transitions. In bulk TiO$_2$, nonadiabatic hoppings occur preferentially when the energy of the polaron-induced gap state approaches the conduction-band
manifold, promoting both electronic de-excitation and, via a Landau-Zener mechanism, excitation from the ground state. In MgO, the predominantly adiabatic character of hole-polaron hopping suppresses these effects, leading to longer charge-carrier lifetimes and an absence of thermally activated excitations. At the rutile TiO$_2$(110) surface, hopping events are rarer than in bulk because the excess electron is strongly stabilized in the subsurface region, leading to correspondingly longer de-excitation times.
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All authors Daniela Mangano, Luca Leoni, Zhongfei Xu, Li-Min Liu, Cesare Franchini
Materials Science
Error-controlled switching between discrete and continuum dislocations in a unified defect framework
Albert Linda
Simulating defects of every dimension together is expensive, and the savings of adaptive methods are rarely tested at equal accuracy. We present a variational framework in which fields, dislocation lines and defect densities share one free energy, one dissipation law and exact ledgers of mass and Burgers vector, so that a region can change its representation without gaining or losing defects. On this basis, an allocator switches the dislocations themselves between discrete particles, where they are sparse, and a continuous density, where they are dense. The switch is made block by block from local counts, conserves the Burgers vector exactly and is controlled by a single threshold. For $5\times10^5$ dislocations, the allocator reproduces the discrete model to within 1% in the sparse region at 14-37 times lower cost, depending on the machine; the advantage grows to 81 times at $10^6$ dislocations, and a threshold calibrated on one ensemble meets its error target on an independent one. For an idealized array of dislocation walls in copper, the allocator is 37.5 times cheaper than particle dislocation dynamics and, at almost the same cost, six times more accurate than continuum dislocation dynamics between the walls. In a three-dimensional copper model coupling grain-boundary cavitation with damage, ligaments left at nominal coalescence delay creep rupture by 25-48% (post hoc sweep). By contrast, grids refined at interfaces gain less than twofold once the active region exceeds about 30% of the domain, so representation switching, rather than grid refinement, is the effective form of adaptivity for defect-rich microstructures.
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Materials Science · Cross-listed from cond-mat.mes-hall
Magnetic field induced modulation of heat transport in CrPS$_4$ probed by TaIrTe$_4$ transverse Seebeck thermometry
Krishnaraajan Sundararajan, Sergio Alvarruiz, Cédric A. Cordero-Silis et al. (+5 more)
Understanding and controlling heat flow in low-dimensional
magnetic materials is central to thermoelectrics and
spin caloritronics. One of the challenges is the absence of sensitive probes of small, field-dependent modulations in thermal transport. Here we demonstrate transverse Seebeck thermometry using exfoliated TaIrTe$_4$ as a probe of thermal conductivity modulated by an external
magnetic field on a van der Waals magnet, CrPS$_4$. With a temperature gradient oriented at $45^\circ$ to its principal crystallographic axes, TaIrTe$_4$ exhibits a transverse thermopower exceeding $200~\mathrm{\mu V\,K^{-1}}$ for 900 nm wide and 30 $\mu$m long electrodes, enabling precise detection of variations in the local temperature gradients. Exploiting this with CrPS$_4$ in a nonlocal geometry, we resolve distinct field dependent thermal conductivity changes associated with both the
spin-flip and
spin-flop
magnetic transitions which we attribute to variations in the
magnon$-$
phonon coupling in CrPS$_4$. At 5 K, the transverse Seebeck response is modulated by more than 8$\%$ by an external
magnetic field, demonstrating strong
magnetic control of heat transport in CrPS$_4$. This all van der Waals platform offers high sensitivity to modulations of thermal conductivity and a broad adaptability to a wide range of exfoliated
magnetic systems.
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All authors Krishnaraajan Sundararajan, Sergio Alvarruiz, Cédric A. Cordero-Silis, Majid Ahmadi, Marcos H.D. Guimarães, Jagoda S\lawińska, Joseph Barker, Bart J. van Wees
Materials Science · Cross-listed from cond-mat.str-el
Beyond Kitaev exchange: $\Gamma'$-driven magnetism in Ag$_3$LiRh$_2$O$_6$
Efrain Insuasti Pazmino, Shi Feng, Ramesh Dhakal et al. (+4 more)
In Kitaev magnets, frustration arises from bond-dependent
spin anisotropic interactions, which can potentially realize sought-after
quantum spin liquid phases. However, material realizations with dominating Kitaev exchange are scarce and the broad parameter space of extended Kitaev models remains largely unexplored experimentally. Here, we use density-functional theory, cluster many-body,
spin-wave, and density-
matrix renormalization calculations to show that the recently discovered honeycomb rhodate Ag$_3$LiRh$_2$O$_6$ hosts an off-diagonal exchange $\Gamma_1'$ that is second in magnitude only to the ferromagnetic Kitaev exchange $K_1$. This combination of $K_1$ and $\Gamma_1'$ explains key experimental observations, an unusually high
magnetic ordering temperature of 94 K at ambient pressure and its rapid decrease under hydrostatic pressure as Ag$_3$LiRh$_2$O$_6$ evolves from ferromagnetic toward zigzag order within the honeycomb planes. Our
spin-wave calculations further predict an unusual
topology of the
magnon bands arising from the $\Gamma_1'$ term in the
spin Hamiltonian of the honeycomb layer. We show that the large trigonal splitting of $t_{2g}$ states enhances $\Gamma_1'$, the hitherto underappreciated term in Kitaev magnets, and opens the way to new interesting regimes of the extended Kitaev model.
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All authors Efrain Insuasti Pazmino, Shi Feng, Ramesh Dhakal, Ioannis Rousochatzakis, Stephen M. Winter, Johannes Knolle, Alexander A. Tsirlin
Materials Science · Cross-listed from cond-mat.str-el
Room-Temperature Metallic 2D Ferromagnetism Stabilized by Quantum Metric
Teng-Fei Ying, Jianqi Zhong, Songyuan Geng et al. (+3 more)
The recent discovery of long-sought dice-
lattice bands in layered electride YCl opens up unprecedented opportunities for studying correlated electrons in real dice
lattice systems. While the weakly dispersive band at the Fermi level is partially filled and density-wave states are expected due to Fermi surface nesting based on conventional theories, the ARPES measurement nevertheless revealed a uniform flat band splitting of 0.5 eV, suggesting unusual ferromagnetism (FM) borne out of the metallic 2D dice
lattice. In this Letter, we propose that the uniform metallic FM order is stabilized by the prominent
quantum metric near topological band crossing points at K and K', which reconstructs the
magnetic instability in the dice metal and tips the density-wave instability toward a uniform FM order. Importantly, our analysis based on random phase approximation (RPA) and Hartree-Fock theory predicts a remarkably high Curie temperature above room temperature for the 2D FM order. These findings establish the first example of a room-temperature 2D metallic magnet stabilized by
quantum metric, which not only exemplifies the fundamental significance of
quantum geometry in solids but also bears far-reaching applications in energy-efficient high-density
magnetic memories.
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All authors Teng-Fei Ying, Jianqi Zhong, Songyuan Geng, Fangjie Chen, Haoxiang Li, Benjamin T. Zhou
Materials Science · Cross-listed from cond-mat.soft
Emergent medium-range order in amorphous silicon
Zhen Zhang, Stephen R. Elliott, Yujie Wang et al. (+1 more)
Medium-range order (MRO) is an important feature of amorphous materials, but its nature in terms of atomic arrangement has remained elusive. Here, using large-scale machine-learning-driven atomistic simulations of amorphous silicon, we probe the MRO of this archetypal network glass. By characterizing the structure in three dimensions, we reveal that the
symmetry of the atomic arrangement around a central atom shows a crossover as a function of distance. At short distances, the structure is determined by local bonding constraints, which evolve from predominantly tetrahedral environments in low-density amorphous silicon to highly coordinated and strongly disordered local environments in very-high-density amorphous silicon. At larger distances, however, distinct cubic- and octahedral-
symmetry patterns emerge in the three-dimensional atomic-density distribution, despite the absence of these
symmetries at shorter length scales. We find that this crossover is accompanied by a quasi-periodic spatial organization of the topological rings in the structure. The characteristic spacing between ring centers matches the length scale of the first sharp diffraction peak (FSDP) in the structure factor, establishing a direct connection between this reciprocal-space signature of MRO and its real-space organization. These results demonstrate that the FSDP, the spatial correlation of the rings, and emergent orientational
symmetries are not independent manifestations of MRO, but reflect different aspects of a common structural organization. Our findings provide a unified real-space picture of MRO in amorphous silicon and suggest that intermediate-range structural order in network glasses emerges from the interplay between local bonding constraints and extended atomic arrangements driven by efficient packing.
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All authors Zhen Zhang, Stephen R. Elliott, Yujie Wang, Walter Kob
Materials Science · Cross-listed from cond-mat.dis-nn
Seismology of Glasses
Zhiyu Cao and Peter G. Wolynes
Aging and relaxation of glasses proceed through localized rearrangements that also generate long-ranged mechanical responses in their surroundings. We develop a theory that treats these rearrangements as internal microseismic sources, and thereby separates the direct effects emerging from an event from the effects from the far-field displacements it generates. These far-field disturbances propagate and relax through the viscoelastic medium through which they move, producing a
stochastic background of weak but numerous perturbations at any given location. Combining the description of local events from the Random First Order Transition theory with this propagating background, we derive a unified equation for the dynamical structure factor of a relaxing glass. The theory identifies a finite wave-vector and time window in which the growing viscoelastic far-field disturbances can produce compressed exponential relaxation, which has been observed using X-ray
photon correlation spectroscopy. At higher wave vectors that resolve local jumps, heterogeneity of the local event dynamics instead produces stretched exponential relaxation. The crossover between these behaviors depends on the event statistics and the scattering phase accumulated across the region reached through viscoelastic propagation from the numerous distant sources.
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Materials Science
Magnetic proximity beyond the interface: Layer-sequence-dependent exchange in WSe$_2$/CrI$_3$ heterostructures
Natalie Kuhn, Marc Schütte, Joachim Emming et al. (+8 more)
Magnetic proximity effects in transition metal dichalcogenide (TMD)/2D-magnet
heterostructures are often described in terms of the magnetization of the interfacial
magnetic layer. Here, we show that this picture is sufficient to describe the neutral-
exciton valley splitting of the TMD, but incomplete for its hole-doped electronic structure. We study a gate-tunable van der Waals
heterostructure composed of monolayer WSe$_2$ in direct contact with trilayer CrI$_3$. By combining spatially and helicity-resolved reflection-contrast spectroscopy with
magnetic circular dichroism, we identify two distinct
magnetic domains in the trilayer CrI$_3$: one with purely antiferromagnetic interlayer coupling and one with a mixed antiferromagnetic (AFM)/ferromagnetic~(FM) coupling. In both domains, the sign of the neutral-
exciton valley splitting of WSe$_2$ switches with the magnetization reversal of the adjacent CrI$_3$ layer. In contrast, helicity-resolved positive-trion spectroscopy of WSe$_2$ reveals a qualitatively different response. While the AFM domain shows a strongly helicity-selective trion resonance, the mixed AFM/FM domain exhibits trion resonances in both helicities. This behavior disappears when all CrI$_3$ layers are aligned in a parallel magnetization direction. Our results demonstrate that charged
excitons are sensitive to the full layer-resolved
magnetic sequence of the adjacent 2D-magnet, revealing
magnetic proximity beyond the interface.
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All authors Natalie Kuhn, Marc Schütte, Joachim Emming, Felix Hellenkamp, Leo Dreyer, Frank Volmer, Kenji Watanabe, Takashi Taniguchi, Lutz Waldecker, Christoph Stampfer, Bernd Beschoten
Materials Science
Pressure engineering of the excitonic moiré-potential landscape and exciton-charge interplay in semiconductor moiré superlattices
Wenbing Li, Tianhao Yue, Wenjian Su et al. (+10 more)
Semiconductor moiré superlattices, owing to strongly bound
excitons and pronounced electronic correlation, have emerged as an intriguing solid platform for exploring correlated bosonic phenomena, where the moiré potential landscape plays a central role. Hydrostatic pressure allows continuous, in-situ tuning of this landscape, but remains underexplored because of experimental challenges. Here we integrate a diamond anvil pressure
cell with high quality dual gated WSe2/WS2 twisted bilayers and perform cryogenic optical spectroscopy. We observe distinct pressure evolutions of moiré intralayer
excitons, which reveal drastic modulation of the excitonic moiré-potential landscape captured by a continuum model and suggest the capability of engineering the
exciton-band
topology. Moreover, we demonstrate efficient pressure control over the interplay between charges and both intralayer and interlayer
excitons: the intralayer charge-transfer
exciton becomes less sensitive to doping, likely due to reduced charge-transfer character; in contrast, the interlayer
exciton exhibits enhanced
exciton-charge repulsion. Our results establish hydrostatic pressure as a powerful tuning knob for engineering bosonic quasiparticles and Bose-Fermi interactions in moiré materials.
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All authors Wenbing Li, Tianhao Yue, Wenjian Su, Zhexu Shan, Chen Xu, Jichen Zhou, Kenji Watanabe, Takashi Taniguchi, Liguo Ma, Yuanfeng Xu, Shiyao Zhu, Yang Gao, Yanhao Tang
Materials Science
ActMOF: Mapping Reticular Synthesis through Active Learning
Hongrui Sheng, Shutian Liang, Reid A. Coyle et al. (+5 more)
Reticular chemistry allows metal-organic frameworks (MOFs) to be designed from their building units, yet their synthesis remains constrained by sparse experimental data, noisy crystallization outcomes, and the absence of
benchmarks for comparing active-learning strategies. While data-driven approaches such as
Bayesian optimization (BO) can improve synthesis success rates, selecting appropriate optimizers beforehand for mapping MOF crystallization landscapes remains largely empirical. Here we present ActMOF, an experiment-grounded
benchmark for comparing search strategies in aluminum-carboxylate MOF synthesis. ActMOF is emulated from experimentally measured microwave syntheses with each encoded condition assigned a crystallinity index calculated based on diffraction peak intensity and full width at half-maximum. By benchmarking policies guided by Gaussian processes (GP), tree ensembles and large
language models (LLM), ActMOF placed the GP family among the leading policies for active learning in sparse synthesis landscapes. It then demonstrated transferability by guiding the microwave synthesis of six reticularly related aluminum MOFs. All six campaigns gave crystalline products within a fixed budget of 12 experiments each, and established a reusable testbed for AI-driven MOF synthesis.
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All authors Hongrui Sheng, Shutian Liang, Reid A. Coyle, Shyam Chand Pal, Peter Walther, Bin Feng, Xinyu Ding, Zhiling Zheng
Materials Science · Cross-listed from cond-mat.str-el
Evidence for hidden order and its potential correlation with electron-hole asymmetry in iridate superlattices
Zhihan Qiao, Han Zhang, Hangtian Wang et al. (+12 more)
Hidden order refers to an order that shapes the properties of
quantum materials yet remains difficult to identify. Here we report signatures of a hidden order in doped iridate superlattices through an unexpected electron-hole asymmetry in the coupling between the insulating state and the antiferromagnetic (AFM) state. While carrier doping suppresses both states, they remain coupled in the electron-doped regime but decouple in the hole-doped regime. Structural analysis rules out octahedral rotation and tilting as the dominant origin of this asymmetry. Instead,
magnetic characterization reveals evidences of a hidden order that only appears in the hole-doped regime. This hidden order emerges above TN and is closely associated with the AFM state, coinciding with an exceptionally strong
magnetic scattering intensity and an anomalously robust
magnetic coherence. Our results highlight that hole-doped iridates can be a promising platform for exploring hidden and unconventional ordering phenomena in
spin-orbit-entangled
quantum materials.
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All authors Zhihan Qiao, Han Zhang, Hangtian Wang, Deyang Li, Haiyang Zhang, Enyang Men, Junlei Jiang, Jingxin Chen, Yizhou Liu, Sang-Youn Park, Xiangnan Xie, MingLiang Tian, Haifeng Du, Ning Hao, Lin Hao