Materials Science
Symmetry-constrained coexistence of charge-three and charge-one Weyl points in nonmagnetic crystals
Ze-Xin Xue, Ke-Xin Pang, Yun-Yun Bai et al. (+2 more)
High-charge Weyl semimetals (WSMs), particularly those hosting charge-three Weyl point (C-3 WPs), have attracted considerable interest owing to their unconventional topological properties and enhanced boundary phenomena. However, ideal C-3 WSMs remain rare, and the
symmetry-constrained coexistence of charge-three and charge-one Weyl point (C-1 WPs) in nonmagnetic
crystals remains largely unexplored. Here, we investigate a representative eight-node Weyl configuration, consisting of two C-3 WPs and six C-1 WPs with opposite chirality, corresponding to two identical $\{3,-1,-1,-1\}$ irreducible Weyl molecules. By combining topological charge conservation with space-group
symmetry analysis, we systematically classify all 230 space groups and identify 12 and 23 candidate groups without and with
spin–orbit coupling (SOC), respectively. First-principles calculations without SOC reveal that the boron allotropes TBR-B$_{48}$ and chiral OBD-B$_{48}$ realize this configuration, hosting hourglass-type and non-hourglass-type C-3 WPs, respectively. Surface-state calculations reveal six Fermi-arc branches at the shared projection of the charge-three pair and three at each individual projection. Reversing the structural chirality of OBD-B$_{48}$ reverses the signs of all Weyl charges, establishing a direct correspondence between
crystal and momentum-space chirality. Furthermore, breaking the protecting $C_6$
symmetry in TBR-B$_{48}$ splits each C-3 WP into three C-1 WPs and reconstructs the surface Fermi arcs. Our work establishes
symmetry-based guidelines for designing and searching for nonmagnetic WSMs hosting charge-three and charge-one Weyl-point coexistence.
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All authors Ze-Xin Xue, Ke-Xin Pang, Yun-Yun Bai, Yanfeng Ge, Yan Gao
Materials Science
Capturing Coordination Core Topology in Metal–Organic Frameworks Using Persistent Mayer Homology
Caleb Simiyu Khaemba, Chun-Long Chen and Guo-Wei Wei
Local coordination cores are critically important in metal-organic frameworks (MOFs) and polyoxometalates (POMs), as they govern the fundamental chemical and structural properties of these materials. Existing methods, including element-resolved persistent homology (ERPH), have limited ability to translate local coordination cores into quantitative, scalable, and interpretable information. Here, we introduce persistent Mayer homology (PMH) to enable the detection of the
geometric variability invisible by classical
topology. By focusing on coordination cores formed by periodic metal-centered heavy-atom, carbon, and donor channels, PMH distinguishes different arrangements of the local coordination environment, linker framework, and potential coordinating atoms. We examine explainable PMH of orders $N=3$ and $N=5$ and separately combine each with ERPH, which characterizes the multiscale organization of chemically defined element groups across the extended framework, to predict eight nitrogen- and oxygen-related adsorption and self-
diffusion properties. The resulting coordination-core PMH representations consistently improve predictive performance over ERPH alone, with the third-order Mayer representation providing the strongest overall performance. These results demonstrate that the inner coordination configurations captured by PMH contain essential structural information that is not fully represented by conventional element-resolved topological descriptors. This finding provides a quantitative interpretable topological framework for understanding local coordination environments and may facilitate the rational design of MOFs and POM-based materials.
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Materials Science · Cross-listed from cond-mat.str-el
Honeycomb Crystal in a Mass-Asymmetric Electron-Hole Bilayer
Shengdu Chai, Wangqian Miao, Yuqiang Li et al. (+3 more)
A two-dimensional electron gas in a uniform neutralizing background forms a triangular Wigner
crystal at low density. In a strongly mass-asymmetric electron-hole bilayer, localized heavy holes instead provide a nonuniform positive background that supports an electron
crystal at densities two orders of magnitude higher than for a homogeneous electron gas in the same material. Here we show that correlated mobile electrons can overturn the preference for triangular order, stabilizing a honeycomb electron-hole
crystal. Using the powerful real-space neural-network variational Monte Carlo in the Born-Oppenheimer limit with fixed holes, we find that increasing the density drives a transition from a triangular electron-hole
crystal to a honeycomb
crystal, which eventually melts into itinerant electrons coexisting with the honeycomb or the triangular hole
lattice at fixed interlayer separation. Relative to triangular order, honeycomb order emerges when gains in electronic kinetic energy and electron-hole attraction outweigh its higher intralayer Coulomb repulsion, a threshold never reached in the rigid point-dipole model. Moreover, the honeycomb hole
lattice supports paramagnetic, antiferromagnetic, and stripe-ordered
spin states. Complex polarization indicates a metal-
insulator transition, while the states on the honeycomb hole
lattice are consistent with a stripe-ordered Dirac semimetal and paramagnetic or antiferromagnetic Mott
insulators via mapping to the half-filled Hubbard model. We further propose a BLG/hBN/WS$_2$-WSe$_2$
heterostructure as a platform for the predicted honeycomb
crystal, at an experimentally feasible density $n\sim10^{11}~\text{cm}^{-2}$.
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All authors Shengdu Chai, Wangqian Miao, Yuqiang Li, Lei Wang, Xi Dai, X.C. Xie
Materials Science · Cross-listed from cond-mat.supr-con
High-Efficiency Field-Free Superconducting Diodes in Mo$_2$N/FePt Bilayers
Juan S. Cruz, Emilio De Biasi, Juan C. Zapata et al. (+3 more)
Near-ideal, field-free superconducting diode behavior is demonstrated in room-temperature-grown Mo$_2$N/FePt bilayers. The response is consistent with remanent FePt stripe domains producing polarity-dependent thresholds for flux entry and
vortex motion. Micromagnetic simulations reveal a periodic stray-field modulation across the stripes and asymmetric field enhancement near their ends at the bridge edges. One current polarity remains nearly dissipationless up to a sizable fraction of the estimated depairing current, whereas the opposite polarity develops dissipation at much lower current, yielding diode efficiencies up to approximately 85% in the thinner bilayer. The nonreciprocity can be continuously tuned by the in-plane
magnetic preparation angle and reversibly switched by reverse-field excursions through the hysteretic reversal of the FePt layer. These results support edge-controlled flux entry and
vortex motion as a route to high-efficiency superconducting diodes.
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All authors Juan S. Cruz, Emilio De Biasi, Juan C. Zapata, Yeonkyu Lee, Jeehoon Kim, Nestor Haberkorn
Materials Science
First-Principles Calculations of the Electron-Hole-Pair Creation Energy in Semiconductors and Dielectrics
Dallin O. Nielsen and Massimo V. Fischetti
We present first-principles calculations of the electron-hole-pair creation energy in
semiconductors and dielectrics, focusing in particular on AlN, 3C-SiC, 4H-SiC, Si, and SiO2. We have employed density functional theory (DFT) to calculate the band structure, density-functional perturbation theory to obtain the
phonon dispersion, and time-dependent DFT (TDDFT) to calculate the electron energy loss function (via the dielectric function). We performed full-band Monte Carlo simulations of electron thermalization for energies up to ~100 eV and calculated the average energy required to excite an electron-hole pair. We calculated pair-creation energies of approximately 12.2, 6.5, 7.3, 3.10, and 16.7 eV/pair for AlN, 3C-SiC, 4H-SiC, Si, and SiO2, respectively. These values are in good agreement with measured data, with the largest discrepancy being that of Si (about 14.9% lower than the accepted experimental value of ~3.6 eV/pair). To improve the agreement for Si, we used the GW approach and the Bethe-Salpeter equation (BSE) to calculate the quasiparticle shifts of the electronic band structure and the dielectric function, respectively. Finally, using the GW/BSE data, we calculated a creation energy of ~3.50 eV/pair. We find that the marked improvement in the accuracy of the calculated creation energy, when using the GW/BSE approach, is primarily attributable to the slight decrease in the magnitude of the electron energy-loss function when using the GW/BSE approach for energies below ~10-15 eV. Overall, it is clear that the competition between
phonon emission and ionization near the intersection of the
phonon scattering and ionization rates is largely responsible for determining the value of the creation energy, with the other major factor being the location and shape of the plasmon peak in the energy-loss function.
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Materials Science
Trust-Limited Machine-Learning-Accelerated Nudged Elastic Band Calculations for Small-Polaron Hopping in Rutile TiO2
Ashish Kumar Singh and Irina V. Lebedeva
Nudged elastic band (NEB) calculations of small-polaron hopping are demanding because nuclear motion is coupled to a self-consistent localized electronic state. Near the charge-transfer region, slow self-consistent-field convergence, localization switching, and competing electronic solutions complicate surrogate-assisted optimization. We develop a Gaussian-process-assisted NEB workflow for this regime and demonstrate electron small-polaron hopping in rutile TiO2 using
spin-polarized density functional theory with a Hubbard U correction (DFT+U ) with SIESTA. A joint energy-force Gaussian process (GP) with a Matérn covariance model advances the elastic band, while active-atom root-mean-square and maximum-atom displacement limits constrain surrogate motion relative to evaluated configurations. Reaching these limits triggers first-principles sampling without requiring full surrogate convergence. Three independently DFT-verified 96-atom [001] calculations using 11, 13, and 15 images and different surrogate settings and GP parameterizations yield barriers of 0.1645, 0.1637, and 0.1640 eV, respectively, spanning 0.793 meV. In the 15-image calculation, repeated central-image sampling activates a separately calibrated local GP during surrogate optimization. Final full-band DFT verification gives a maximum projected NEB force of 0.0346 eV/Å. A 324-atom calculation yields a lower barrier of 0.1302 eV, indicating supercell sensitivity and demonstrating feasibility at larger GP observation dimension. The workflow combines controlled surrogate extrapolation, targeted charge-transfer-region interpolation, and independent DFT verification to obtain polaron migration pathways, emphasizing reproducible barriers and full-band force convergence.
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Materials Science
Molecular Precursor Chemistry Shapes Early-Stage Reaction Pathways in Nitrogen-Doped Carbon Nanotube Synthesis
Narayan N. Som, Lukasz Nowicki, Tomasz Gizewski et al. (+10 more)
The structural characteristics of carbon nanotubes are usually discussed in terms of processes occurring during nanotube nucleation and subsequent growth from an already formed catalyst nanoparticle. Here, we show that their structural trajectory can begin much earlier, within the first nanoseconds of precursor decomposition and catalyst formation. We combine experiment and reactive molecular dynamics to compare nitrogen-free CNT synthesis with two closely related aromatic nitrogen precursors, pyridine and pyrazine, containing one and two nitrogen atoms per molecule, respectively. Experimentally, both nitrogen-containing precursors promote bamboo-like CNT formation and produce substantially more structurally disordered CNTs than the nitrogen-free reference. Notably, nitrogen incorporation does not scale simply with the amount of nitrogen supplied, demonstrating a strong contribution from precursor chemistry. Reactive molecular dynamics reveals that nitrogen-containing precursors significantly modify local Fe-carbon and Fe-SiO2 interactions during catalyst
evolution, while pyridine and pyrazine exhibit distinct decomposition pathways, with pyrazine showing significantly greater decomposition within the simulated timescale. These results demonstrate that precursor chemistry influences the local chemical environment and early catalyst
evolution, highlighting its potential role in the initial stages of CNT growth.
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All authors Narayan N. Som, Lukasz Nowicki, Tomasz Gizewski, Karolina Z. Milowska, Anna Wroblewska, Caghan Tuncer, Maciej Trzaskowski, Olga Iwasinska-Kowalska, Tomasz Plocinski, Mariusz Zdrojek, Krzysztof K. Koziol, Malgorzata Jakubowska, Agnieszka Lekawa-Raus
Materials Science
Engineering Ferroelectric Phases in BaTiO$_3$ Films via Buffer-Layer Induced Misfit Strain Reversal
A.S. Mikheykin, N.V. Lyanguzov, A.S. Konstantinov et al. (+4 more)
Controlling ferroelectric phase
symmetry through strain engineering is crucial for tailoring polarization
topology and functional properties in oxide-based devices. Here, we show that a thin conductive buffer layer can override substrate-induced strain in BaTiO$_3$ (BTO) films on MgO. Although the
lattice parameter of MgO(001) would be expected to induce tensile misfit strain, in 500~nm BaTiO$_3$ films the thermal-expansion mismatch dominates, resulting in effective compressive stress upon cooling. Inserting a 50-nm La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) buffer layer reverses the effective strain state from compressive to tensile. Using temperature-dependent polarized Raman spectroscopy, X-ray diffraction, and piezoresponse force microscopy, we reveal an unconventional phase sequence upon cooling: paraelectric $\rightarrow$ orthorhombic ($\textit{aa}$-phase, $\sim$407 K) $\rightarrow$ monoclinic ($\textit{r}$-phase, $\sim$300-345 K), characterized in-plane and tilted polarization components. The LSMO layer not only serves as a bottom electrode but also modifies the strain state, while interfacial charge redistribution induces a built-in electric field, evidenced by self-polarization and asymmetric PFM hysteresis. These findings highlight the critical role of conductive buffer layers in controlling ferroelectric
symmetry and enabling oxide
heterostructures with tailored polarization textures for low-power spintronics, tunable microwave devices, and neuromorphic computing.
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All authors A.S. Mikheykin, N.V. Lyanguzov, A.S. Konstantinov, V.B. Shirokov, E.D. Linnik, T. Bondar, A.G. Razumnaya
Materials Science
Domain-wall-to-domain interconversion in a polar conducting oxide
Martin F. Sarott, Majid Ahmadi, Johanna van Gent González et al. (+13 more)
Domain walls in ferroic
crystals are topological defects with a
symmetry distinct from the domain interior, allowing them to display functionalities that are otherwise forbidden in the host material. Despite their unique properties, domain walls are strictly confined to two-dimensional interfaces, which hinders unveiling their true nature and limits their applicability. Here, we demonstrate reversible dimensionality control by expanding nanoscale domain walls into three-dimensional functional regions in polar epitaxial tungsten trioxide ($\text{WO}_3$). This domain-wall-to-domain interconversion is enabled by the conducting, non-polar domain walls adopting the parent-phase structure. An alternating electric field applied through a scanning probe tip induces localized heating, which expands this domain-wall phase into the adjacent polar domains. This approach enables reversible spatial control to switch between mutually exclusive properties of domains (polarity) and domain walls (conductivity), offering a new paradigm for reconfigurable oxide electronics.
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All authors Martin F. Sarott, Majid Ahmadi, Johanna van Gent González, Ewout van der Veer, Mads C. Weber, Jacopo Pinna, Daniel A. Chaney, Arijit Sinha, Hamideh Hassani, Horatio R. J. Cox, Thomas Perrault, Amir Sabet Ghorabaei, Maria A. Loi, Philippe Ghosez, Bart J. Kooi, Beatriz Noheda
Materials Science
Real-space obstruction control of the shift current in two-dimensional Quantum Spin Hall insulators
Michele Bagaglini, Mattia Iannetti, Jonas Erhardt et al. (+4 more)
The search for materials exhibiting a large bulk photovoltaic effect has recently expanded to low-band-gap systems capable of operating in the infrared regime, with potential applications in optoelectronics. Among the microscopic mechanisms contributing to this phenomenon, the shift current is one of the dominant sources of photocurrent generation. Owing to its
geometric origin, the shift current is not only determined by the optical transition probability but also by the real-space displacement associated with the optical excitation, making non-centrosymmetric materials with obstructed electronic wave functions particularly promising candidates. In this work, using a tight-binding model of a
quantum spin Hall
insulator on a triangular
lattice, we investigate the nonlinear photocurrent across trivial,
quantum spin Hall, and higher-order topological insulating phases. We show that obstructed topological phases exhibit a substantially enhanced shift-current response, despite the similar electronic band structure. We identify the origin of this enhancement in optical transitions between states belonging to distinct Wannier-center sectors, which allow for a large real-space displacement upon photoexcitation and, depending on the topological phase, control the sign of the shift current. Our results extend the search for controllable bulk photovoltaic effects to materials characterized by real-space electronic obstruction and identify indenene, a monolayer of In on SiC(0001), as a promising candidate for realizing this phenomenon.
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All authors Michele Bagaglini, Mattia Iannetti, Jonas Erhardt, Jörg Schäfer, Ralph Claessen, Giorgio Sangiovanni, Gianni Profeta
Materials Science
Interlayer Registry Controls Polar Topology in Twisted Bilayer h-BN
Di Fan, Changming Ke and Shi Liu
Twisting van der Waals bilayers creates a moir'e stacking field with periodically varying local interlayer registry, enabling spatially patterned polarization. However, a systematic understanding of how this registry-controlled polar
topology evolves with twist angle, temperature, and mechanical strain is still lacking. Here, using first-principles-trained deep-potential molecular dynamics simulations, we show that spatially varying interlayer registry governs the polarization texture and can be directly tuned by twist and relative layer deformation. As the twist angle decreases, the moir'e polarization texture evolves from compact, nearly circular
vortex-like patterns to extended triangular AB/BA domains. This crossover arises from enhanced
lattice relaxation at small twist angles, which expands low-energy, oppositely polarized AB/BA regions and confines in-plane polarization mainly to domain boundaries. Despite this reconstruction, the local in-plane winding remains tied to interlayer registry and persists up to 1000 K, indicating robust
topology against thermal fluctuations. We further show that the mechanical response is dictated by whether deformation changes the relative registry: homogeneous deformation of both layers produces only weak distortions, whereas layer-selective deformation strongly reconstructs the moiré polarization texture. A mismatch-
matrix registry-mapping model is developed to capture this response, explaining deformation-induced changes in
vortex radii at larger twist angles and triangular-domain geometry at smaller twist angles. These results identify interlayer registry as the central control parameter for forming and tuning moir'e polar
topology in twisted bilayer h-BN.
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Materials Science
Theoretical Investigation of Oxygen-Vacancy Diffusion in SrTiO$_3$ using Neural Network Potentials
Kazutaka Nishiguchi, Ryota Yamamoto and Seiichiro Ten-no
Oxygen-vacancy formation and
diffusion play important roles in determining the electronic and atomic transport properties of SrTiO$_3$ (STO). Accurate analysis of such point defects requires sufficiently large-scale and long-time molecular dynamics (MD) simulations; however, direct investigations of oxygen-vacancy dynamics using ab initio MD (AIMD) based on density functional theory (DFT) are limited to relatively small systems and short time scales because of their high computational cost. In this study, we develop a neural network potential (NNP) for pristine and oxygen-deficient STO using a reference
dataset generated from AIMD simulations. The trained NNP model accurately reproduces the DFT reference energies, atomic forces, and virials for both pristine STO and STO containing an oxygen vacancy. The NNP also reproduces the supercell-size dependence of the total energies and oxygen-vacancy formation energies, including the formation energy extrapolated to the dilute limit. Large-scale and long-time MD simulations using the NNP (NNP-MD) are then performed to investigate oxygen-vacancy
diffusion. The resulting oxygen-vacancy
diffusion coefficients show substantially better agreement with experimental data than those obtained from conventional classical MD simulations. An Arrhenius analysis yields an oxygen-vacancy migration enthalpy of 0.64 eV, in close agreement with the experimental value of 0.67 eV. These results demonstrate that NNPs trained on first-principles data provide an accurate and computationally efficient framework for investigating defect formation and long-time vacancy transport in perovskite oxides.
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Materials Science · Cross-listed from cond-mat.supr-con
Superconductivity from altermagnetic fluctuations: the crucial role of sublattice polarization
Mats Barkman, Andreas Kreisel and Brian M. Andersen
Unconventional superconductivity in correlated systems often appears in the vicinity of a magnetically ordered state. This situation is also relevant for altermagnets, characterized by a nonrelativistic
spin-split electronic structure in the presence of Néel order. Many proposed altermagnetic candidates, however, never cross the
magnetic instability. We study superconductivity arising from altermagnetic fluctuations in such systems and show that the sublattice polarization (SLP) of the normal-state bands plays a pivotal role in determining the superconducting state. SLP, an inherent property of altermagnetic band structures that persists even without
magnetic order, prevents Cooper pairs from forming between different sublattices. This suppresses pairing mediated by the nearest-neighbor antiferromagnetic exchange, which favors
spin-singlet superconductivity, and leaves longer-range same-sublattice bonds dominant. When the next-nearest-neighbor exchange is ferromagnetic, as expected for frustration-free Néel order, this results in
spin-triplet superconductivity. This mechanism is fundamentally different from that in altermagnets with long-range Néel order, where the
spin-split Fermi surfaces favor equal-
spin pairing. Finally, when longer-range interactions in the disordered phase instead favor singlet pairing, SLP leads to singlet states with characteristic properties distinct from nearest-neighbor pairing states.
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Materials Science · Cross-listed from cs.AI
PXRD-Bench: How Close Are We to Determining Crystal Structures from Powder Diffraction?
Dongyeop Woo, Nofit Segal, Nayoung Kim et al. (+3 more)
Determining
crystal structures from powder X-ray diffraction (PXRD) would enable routine characterization of newly synthesized materials, including those absent from reference databases. Generative models offer a promising approach, but existing evaluations remain fragmented and largely assume single-phase samples with known composition. To fill this gap, we introduce PXRD-Bench, a unified
benchmark that extends evaluation to unknown per-element atom counts and recovery of both structures in two-phase mixtures. It provides approximately 4.1 million training structures with simulated PXRD, tests generalization to unseen compositions and structural prototypes, and evaluates recovery from experimental PXRD after excluding structurally matching training entries. To provide a strong reference baseline, we also introduce Bragglite, a PXRD-to-structure model developed through a systematic study of PXRD modeling choices. It achieves a 44.2% Top-1 match rate on experimental RRUFF patterns with known composition, 24.6% above the strongest prior baseline. Further analysis yields several key findings: some models fail to benefit from experimental PXRD, while generalization to unseen structural prototypes and recovery from two-phase mixtures remain challenging. Together, our
benchmark, systematic studies, and Bragglite clarify the capabilities and limitations of current PXRD-to-structure models.
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All authors Dongyeop Woo, Nofit Segal, Nayoung Kim, Minkyu Kim, Rafael Gomez-Bombarelli, Sungsoo Ahn
Materials Science
Modelling the dynamics of the martensitic transformation in Ni$_2$MnGa with machine-learning force-fields
Markus E. Gruner, Yulia Klunnikova, Mike J. Bruckhoff et al. (+2 more)
The martensitic transformations in stoichiometric Ni$_2$MnGa and related Heusler
alloys are governed by a delicate interplay between electronic structure, magnetism, and
lattice dynamics. While density functional theory (DFT) has successfully mapped the energy landscape of modulated martensites, it remains computationally prohibitive for capturing finite-temperature dynamics across relevant length and time scales. Here, we bridge this gap by constructing DFT-trained machine-learning force-fields (ML-FF) interpolated from ab initio molecular dynamics. We demonstrate that ML-FF trained on DFT data can reproduce key features of Ni$_2$MnGa, including the soft TA$_2$
phonon and a preference for nanotwinned martensites. Using classical molecular dynamics simulations, we explore the impact of adaptive nanotwinning on the austenite-martensite transition, which facilitates the dynamics of both, forward and backward transformation. We demonstrate, that the negative twin boundary energy along the entire transformations path predicted by DFT for $T=0$, supports the formation of ordered modulated martensites at finite temperatures. Our results pave the way for large-scale simulations of
magnetic shape
memory alloys with near-DFT accuracy.
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All authors Markus E. Gruner, Yulia Klunnikova, Mike J. Bruckhoff, Konstatin P. Skokov, Olga N. Miroshkina
Materials Science
Decoupling Trap States in Amorphous Oxide Semiconductor Transistor Using a Conductive-Semiconducting-Conductive MOS Structure
Kai Chen, Wei Zhang, Xuanyao Fong et al. (+2 more)
We propose a novel amorphous oxide
semiconductor (AOS)-based conductive-semiconducting-conductive (CSC) MOS test structure to effectively sense, discriminate, and analyze distinct trap-induced conductance losses in AOS transistors. In conventional test structures, non-ideal metal-AOS contacts convolute the conductance loss generated by various trap states. The CSC architecture mitigates these contact-related artifacts, enabling the decoupling of interface states and shallow states. Furthermore, the contributions from leakage, series resistance, and device-geometry effects are identified and calibrated. Our results yield bias-resolved trap profiles and reveal three distinct regimes: (1) In the depletion region, interface states dominate the conductance loss. These states exhibit sub-microsecond time constants and their density increases slightly with deeper depletion, which is associated with donor-like states. (2) From weak to moderate accumulation, shallow states become the primary contributor, displaying a Gaussian-like volumetric density-of-states distribution with response times spanning from microseconds to nanoseconds. (3) In the strong accumulation regime, interface states regain dominance with an increased state quantity, while their time constants remain invariant. These bias-resolved profiles clarify how different trap populations impact AOS transistors under distinct operating conditions, providing intuitive metrics for understanding reliability degradation. Consequently, the CSC structure offers a simple, scalable, and robust platform for trap characterization in AOS transistors.
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All authors Kai Chen, Wei Zhang, Xuanyao Fong, Shengman Li, Yunlong Li
Materials Science · Cross-listed from cond-mat.soft
Thermal softening of the yield stress in glasses with different stability
Tianze Wan and Ludovic Berthier
The yielding of amorphous solids has been extensively studied in the athermal limit, but the influence of thermal fluctuations is much less understood, in particular for glasses of different stability. Using molecular dynamics simulations of a model glass where the swap Monte Carlo
algorithm can be employed, we study the yield stress at finite temperature and shear rate, both in steady flow and at shear start-up, over a broad range of glass stability. Thermal fluctuations soften both the dynamic yield stress in steady state and the start-up yield stress. In all cases, the temperature dependence is compatible with the $T^{2/3}$ law expected for thermally activated yielding near a saddle-node instability, with no systematic dependence of the exponent on stability or shear rate. Extrapolations to zero temperature recover the athermal yield stresses. The amplitude of the softening at start-up, by contrast, depends strongly on stability: highly stable glasses are much less sensitive to temperature than poorly annealed ones. A description of yielding at finite temperature must therefore account explicitly for the stability of the glass.
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Materials Science
Angle-Resolved Photoemission as a Sensitive Probe of Surface Quality: Sputtered versus Annealed Cu(001)
Hyeonhee Na, Jeonghwan Oh, Jinju Lee et al. (+5 more)
Angle-resolved photoemission spectroscopy (ARPES) requires a well-ordered surface, whose quality is routinely judged from low-energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS). We compare LEED, XPS, and ARPES of a Cu(001) single
crystal measured in situ at four stages of surface preparation: as-prepared, after aging for 24 h at 6 K, after Ar$^+$ sputtering, and after annealing. The sputtered and annealed surfaces show nearly identical $(1\times1)$ LEED patterns and Cu 2$p$ core levels, but the sputtered surface yields a momentum-independent ARPES spectrum, and the band dispersion recovers after annealing. We attribute this contrast to how each probe responds to sputtering-induced defects: LEED reflects the average
lattice, which remains periodic, whereas ARPES reflects the electronic states, whose
crystal momentum is no longer well defined. Our results indicate that a sharp LEED pattern and clean core-level spectra do not guarantee a surface suitable for ARPES.
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All authors Hyeonhee Na, Jeonghwan Oh, Jinju Lee, Hanjun Sim, Myeongun Go, Jimin Sohn, Jeonggu Kang, Byungmin Sohn
Materials Science · Cross-listed from physics.ins-det
A Low-Temperature Tool for Acousto-electric Detection
Rohit Mandlik and Sunil Nair
We have developed an apparatus for the measurement of the acousto-electric effect (AEE) from room temperature to
liquid nitrogen temperatures. The AEE is excited by bulk acoustic waves (BAWs) for which a lithium niobate piezoelectric actuator is employed. A very low background noise level is realized through careful electrical and mechanical design of the setup. The validity of the setup is tested by measuring the AEE in heavily doped P-type and N-type silicon. The opposite sign of the AEE signal was seen for both samples, showing dependence of the signal on the type of charge carrier being dragged by acoustic waves. The signal showed quadratic dependence on the driving voltage, which is consistent with the AEE literature. Further, a temperature dependence of the AEE signal was measured, which exhibits a monotonic increase with a rise in temperature. The ability to probe the AEE in bulk samples at low temperatures makes this setup a promising tool to investigate the AEE and related phenomena in different materials at cryogenic temperatures.
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Materials Science · Cross-listed from cond-mat.soft
Defining Thixotropy
Yogesh M. Joshi and Ronald G. Larson
Originally coined 100 years ago to represent a shear-reversible sol-gel transition, the range of the term "thixotropy" has gradually expanded to encompass time-dependent changes in viscosity. Since this risks confusing "thixotropy" with ordinary nonlinear viscoelastic behavior, in this work we seek simple, historically faithful, quantifiable, and experimentally testable definitions of "thixotropy" that avoid this confusion. By analysing both historical tradition and published experimental data, we arrive at three complementary definitions. Definition 0 provides an idealized, purely inelastic reference useful primarily for recognizing thixotropy in a constitutive equation. Definitions 1 and 2, which are more practical, require, respectively, unusually large strains to reach steady state, and unbounded growth of the material relaxation time during rest. Definition 1 can apply in either shear-rate or stress-controlled modes, with the latter encompassing the so-called "viscosity bifurcation." These criteria are tested across diverse materials that we identify as thixotropic based on their responses clearly exceeding their viscoelastic reference scales. The framework is deliberately phenomenological and does not require specific microscopic mechanisms, allowing diverse materials to be described within a common rheological
language, as is typical for rheological terminology. We believe that these definitions provide a practical framework for assigning thixotropy a more definite place in rheological taxonomy.
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Materials Science · Cross-listed from cond-mat.str-el
Field-driven phase transition crossover in kagome antiferromagnet Mn$_{3-x}$Co$_x$Sn
Shubhankar Paul and Chanchal Sow
Mn$_3$Sn exhibits a complex
magnetic phase diagram with multiple
symmetry-breaking phenomena. Minute electron doping at the Mn site breaks the kagome
lattice symmetry in Mn$_3$Sn. In this work, we exploited this to tune the order of the
magnetic phase transition using magnetocaloric effect in Mn$_{3-x}$Co$_x$Sn single
crystals. Pristine Mn$_3$Sn shows metallic behaviour with a
spin-reorientation transition at 278 K, which shifts to 175 K upon Co doping. Additionally, Co doping also induces a weak-ferromagnetic transition near $\approx 210$ K. The effect of Co doping results inverse to conventional magnetocaloric effect, with enhanced
magnetic entropy change. Further, the scaled
entropy change reveals a field-driven
magnetic phase transition crossover from first order to second order in Mn$_{2.75}$Co$_{0.25}$Sn
crystal. Based on experimental data, a new phase diagram is constructed, depicting the field
evolution of various
magnetic orders.
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Materials Science · Cross-listed from cond-mat.mes-hall
Chirally pinned flat bands, helical minibands, and bias-controlled topology of Jackiw-Rebbi states in a periodically modulated Dirac mass texture
Tao Zhou
Flat bands amplify interactions into correlated phases, and topological bound states are robust by principle; combining the two in a model that is both exactly analyzable and experimentally accessible is therefore especially desirable. Here we show that a square-
lattice model with a slowly modulated Dirac mass texture, $m(x)=m+m_0\cos(2\pi x/L)$ with $L$ up to hundreds of sites, provides such a setting, without engineered geometries,
lattice-scale textures, or long-range hoppings. Exact nesting reduces the problem, independently at each transverse momentum $k_y$, to a $1+1$ dimensional Dirac
Hamiltonian with a position-dependent mass: every simple zero of $m(x)$ binds Jackiw-Rebbi zero modes, and the two walls of a period form an effective Su-Schrieffer-Heeger ring. The model interpolates between a chirally pinned flat band at large $L$, a helical miniband whose nodes are enforced by a boundary phase of the ring, and a bias-dimerized regime in which the sign of the bias sets a winding number. A central result is that the miniband bandwidth is not a single scale: a max-min measurement conflates three widths of different origin, the helical height $W_{\rm JR}$ exponential in the period, the zone-edge upturn $W_{\rm edge}\propto L^{-2/3}$ dominating at large $L$, and a bias bump exponential in $L$, so the flat band is robust against bias in the thermodynamic limit. We analyze two
lattice realizations, a two-orbital model with modulated inter-orbital hybridization and a single-orbital bond-order texture sharing the nodal physics while leaving the van Hove points gapless, and propose experiments on cold-atom superlattices, Kekule-ordered
graphene, STM designer
lattices, and microwave arrays.
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Materials Science
Vibrational Fingerprints of Competing Structural and Polar Phases in CuInP2S6
Pegah Mohammadi and Sobhit Singh
Layered van der Waals CuInP2S6
crystals exhibit a rich sequence of temperature- and pressure-driven phase transitions, giving rise to multiple structural phases with distinct physical properties. Despite extensive experimental and theoretical efforts, unambiguous identification of these phases remains challenging because of their structural similarities and complex vibrational responses. In this work, we employ first-principles density functional theory calculations to systematically investigate the vibrational properties of the reference paraelectric C2/c and P-31c phases and their corresponding dynamically stable ferroelectric Cc and P31c phases, as well as the antiferroelectric P-1 and P-3 phases. From calculated
phonon spectra and
symmetry analysis, we determine the Raman- and infrared-active modes of each candidate structure and identify characteristic vibrational fingerprints that enable their phase determination through vibrational spectroscopy. Furthermore, using Porto notation, we establish polarization- and
crystal-orientation-dependent Raman selection rules for different backscattering geometries and identify the modes that are expected to emerge or vanish under specific experimental configurations. Thus, our results provide a comprehensive theoretical framework for interpreting Raman and infrared measurements of CuInP2S6 and for reliably identifying its competing structural, ferroelectric, and antiferroelectric phases across temperature- and pressure-driven phase transitions.
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Materials Science
Nonrelativistic Optically-Induced Spin Torque in Noncollinear Magnets
Zhiyuan Li and Jian Zhou
Manipulating
spin using contactless and non-invasive optical approaches is one of the forefront topic in the modern spintronic science and technology. Prior studies on optically-induced
spin reorientation usually scales with
spin-orbit coupling strength, setting a limitation on composing heavy elements. In this work, we extend such a limit into nonrelativistic regime by exploring noncollinear
magnetic configuration. Using a general
spin group-theoretical investigation, we show how the symmetric operators in both
spin and
lattice spaces control the
spin torque and
quantum geometry of Bloch wavefunction–including both
quantum metric and Berry
curvature. We describe their site-resolved
spin symmetries and unravel their selection rules. Furthermore, we adopt a Kagomé
lattice model and a realistic material family to showcase the local
spin torque under light irradiation. Since the nonrelativistic
spin splitting usually spans on the order of electron-volt, significantly larger than typical
spin-orbit induced splitting, the nonrelativistic light-induced
spin torque is concomitantly much stronger. This work extends the previous opto-spintronics from relativistic to nonrelativistic limit, significantly broadening its realization platform.
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Materials Science · Cross-listed from quant-ph
Measuring higher-order bulk topology in a programmable quantum simulator
Pratik Sathe, Niclas Heinsdorf, Majid Kheirkhah et al. (+13 more)
Topological
insulators lie outside the standard Landau paradigm: Instead of being characterized by local order parameters and spontaneous
symmetry breaking, their defining properties are encoded in the global structure of their
quantum states and manifested as robust boundary states. Crystalline higher-order topological
insulators can extend this principle by hosting localized corner modes in two and higher dimensions. Although these boundary modes can be detected spectroscopically through the local density of states, determining the underlying bulk
topology, for example through nested Wilson loops, remains an outstanding experimental challenge. Here we use up to 728
qubits in a superconducting analogue-digital
quantum simulator to realize and probe a hierarchy of one-, two-, and three-dimensional topological
insulators governed by effective tight-binding
Hamiltonians. By reconstructing complex propagators from real-space measurements, we obtain complementary boundary and bulk characterizations: local densities of states reveal localized boundary modes, whereas experimentally reconstructed band projectors yield bulk topological invariants, culminating in a three-dimensional octupole moment extracted through third nested Wilson loops. These results establish a route to realizing, characterizing, and manipulating topologically protected states in programmable three-dimensional
quantum matter.
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All authors Pratik Sathe, Niclas Heinsdorf, Majid Kheirkhah, Rahul Deshpande, Fabio Altomare, Andrew J. Berkley, Martin Dehn, Richard Harris, Emile Hoskinson, Stefan Paul, Gabriel Poulin-Lamarre, Jack Raymond, Chris Rich, Mohammad H. Amin, Marcel Franz, Andrew D. King
Materials Science
An empirical model for deriving information on ion dynamics from $\mu$SR data via the conventional Kubo-Toyabe function analysis
Ryosuke Kadono
We present an empirical model that analytically relates the parameters of the extended Kubo-Toyabe (KT) function $G_z^{\rm EA}(t;\Delta,\nu_{\rm i},Q)$, which describes
muon spin relaxation ($\mu$SR) induced by jump
diffusion of ions using the Edwards-Anderson parameter $Q$, to those of the conventional KT function $G_z^{\rm KT}(t;\Delta_{\rm KT},\nu_{\rm KT})$ that serves as an approximation of $G_z^{\rm EA}(t)$. The proposed formulae successfully reproduce the anomalous temperature dependences of the linewidth $\Delta_{\rm KT}(T)$ and the fluctuation rate $\nu_{\rm KT}(T)$ which are artifacts observed upon analyzing $\mu$SR data on ion
diffusion using $G_z^{\rm KT}(t)$. Applying this model to $\Delta_{\rm KT}$ and $\nu_{\rm KT}$ published in the literature of battery materials yields activation energy $E_{\rm i}$ and pre-exponential factor $\nu_{\rm i0}$ in the Arrhenius equation for ion
diffusion, $\nu_{\rm i}(T)=\nu_{\rm i0} e^{-E_{\rm i}/kT}$, that are in excellent agreement with those deduced using other techniques, transforming peculiar artifacts into a powerful diagnostic tool.
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