Materials Science
Active-Learning Inspired $\textit{Ab Initio}$ Theory-Experiment Loop Approach for Management of Material Defects: Application to Superconducting Qubits
Sarvesh Chaudhari, Cristóbal Méndez, Rushil Choudhary et al. (+11 more)
Surface
oxides are associated with two-level systems (TLSs) that degrade the performance of niobium-based superconducting
quantum computing devices. To address this, we introduce a predictive framework for selecting metal capping layers that inhibit niobium
oxide formation. Using DFT-calculated oxygen interstitial and vacancy energies as thermodynamic descriptors, we train a logistic regression model on a limited set of experimental outcomes to successfully predict the likelihood of
oxide formation beneath different capping materials. This approach identifies Zr, Hf, and Ta as effective
diffusion barriers. Our analysis further reveals that the
oxide formation energy per oxygen atom serves as an excellent standalone descriptor for predicting barrier performance. By combining this new descriptor with
lattice mismatch as a secondary criterion to promote structurally coherent interfaces, we identify Zr, Ta, and Sc as especially promising candidates. This closed-loop strategy integrates first-principles theory, machine learning, and limited experimental data to enable rational design of next-generation materials.
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All authors Sarvesh Chaudhari, Cristóbal Méndez, Rushil Choudhary, Tathagata Banerjee, Maciej W. Olszewski, Jadrien T. Paustian, Jaehong Choi, Zhaslan Baraissov, Raul Hernandez, David A. Muller, B. L. T. Plourde, Gregory D. Fuchs, Valla Fatemi, Tomás A. Arias
Materials Science
Epitaxially-stabilized growth of wüstite FeO on 4H-SiC
Faisal Kimbugwe, Marzieh Baan, Alexandra Fonseca Montenegro et al. (+2 more)
Iron(II) monoxide (FeO) is thermodynamically stable in the halite (wüstite) structure only at elevated temperatures in a typically non-stoichiometric, Fe-deficient, Fe$_{1-z}$O form that tends to phase separate and/or transform into metallic $\alpha$-Fe and magnetite Fe$_3$O$_4$ at ambient conditions. Here we report on the successful growth of up to 180 nm thick $(111)$-oriented FeO heteroepitaxial films on slightly
lattice-matched 4H-SiC$(0001)$ using molecular beam epitaxy (MBE). The films have flat, terraced surfaces with tall multi-layer steps. X-ray diffraction (XRD), high-resolution scanning transmission electron microscopy (S/TEM), energy-dispersive X-ray spectroscopy (EDS), and core-level electron energy loss spectroscopy (EELS) collectively confirm the epilayer as phase-pure wüstite FeO, with atomically sharp FeO/SiC interfaces. The films are found to exhibit a slight misfit strain-induced rhombohedral distortion that does not appear to vary over the range of thicknesses examined. These results demonstrate the power of epitaxial stabilization for integrating a thermodynamically unstable, yet functionally interesting material with a commercially available and technologically important
semiconductor platform.
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All authors Faisal Kimbugwe, Marzieh Baan, Alexandra Fonseca Montenegro, Roberto C Myers, Tyler J Grassman
Materials Science
Spin polarization engineering in $d$-wave altermagnets
Mohsen Yarmohammadi, Marco Berritta, Marin Bukov et al. (+3 more)
Altermagnets host unconventional
spin-polarized bands despite zero net magnetization, but controlling their
spin structure remains challenging. We propose a multi-field approach to engineer
spin polarization in $d$-wave altermagnets using gating, optical driving, and in-plane electric fields, which enable tunable and switchable polarizations along multiple directions. Optical driving induces out-of-plane ($z$) polarization, while gating and in-plane fields generate $x$- and $y$-polarizations via the Edelstein effect, all of which are experimentally detectable. We further find that
spin- and band-selective doping induces
chiral optical activity, a feature unique to altermagnets. Our approach provides a versatile route for full control of
spin polarization in altermagnets.
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All authors Mohsen Yarmohammadi, Marco Berritta, Marin Bukov, Libor Šmejkal, Jacob Linder, Peter M. Oppeneer
Materials Science
Slow-phonon control of spin Edelstein effect in Rashba $d$-wave altermagnets
Mohsen Yarmohammadi, Jacob Linder and James K. Freericks
Altermagnets have zero net magnetization yet feature
spin-split bands. Here, we investigate how slow
lattice vibrations (
phonons) influence both the intrinsic and externally induced
spin polarizations in two-dimensional $d$-wave altermagnets. For the induced
spin polarization, we employ a Rashba continuum model with electron-
phonon coupling (EPC) treated at the static Holstein level and analyze the
spin Edelstein effect using the Kubo linear-response formalism to probe EPC-induced contributions. We find that, under a specific
symmetry-lowering pattern such as a piezomagnetically active strain that explicitly breaks the inherent $C_4 \mathcal{T}$
symmetry, moderate-to-strong EPC progressively suppresses the induced polarization via both intraband and interband channels, with a threshold coupling marking the onset of complete
spin Edelstein depolarization. The depolarization arises from a
phonon-induced energy renormalization that leads to a complete collapse of the
Fermi surface. While depolarization can occur even in the Rashba non-altermagnetic phase, it remains isotropic. The presence of altermagnetism makes it anisotropic and breaks the conventional antisymmetry between
spin susceptibilities that occurs with pure
spin-orbit coupling, rendering the effect highly relevant for spintronic applications. We further investigate how the
phonon coupling to the altermagnetic order, Rashba
spin-orbit strength, and carrier doping collectively tune the depolarization. Our findings demonstrate that static phononic effects offer a powerful means for on-demand control of
spin polarization, enabling reversible switching between
spin-polarized and depolarized states–a key functionality for advancing
spin logic architectures and optimizing next-generation spintronic devices.
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Materials Science · Cross-listed from cond-mat.supr-con
Uncovering origins of heterogeneous superconductivity in La$_3$Ni$_2$O$_7$ using quantum sensors
Srinivas V. Mandyam, Esther Wang, Zhipan Wang et al. (+7 more)
The family of nickelate
superconductors have long been explored as analogs of the high temperature cuprates. Nonetheless, the recent discovery that certain stoichiometric nickelates superconduct up to high $T_c$ under pressure came as a surprise. The mechanisms underlying the superconducting state remain experimentally unclear. In addition to the practical challenges posed by working in a high pressure environment, typical samples exhibit anomalously weak diamagnetic responses, which have been conjectured to reflect inhomogeneous `filamentary' superconducting states. We perform wide-field, high-pressure, optically detected
magnetic resonance spectroscopy to image the local diamagnetic responses of as grown La$_3$Ni$_2$O$_7$ samples in situ, using nitrogen vacancy
quantum sensors embedded in the diamond anvil
cell. These maps confirm significant inhomogeneity of the functional superconducting responses at the few micron scale. By spatially correlating the diamagnetic Meissner response with both the local tensorial stress environment, also imaged in situ, and stoichiometric composition, we unravel the dominant mechanisms suppressing and enhancing superconductivity. Our wide-field technique simultaneously provides a broad view of sample behavior and excellent local sensitivity, enabling the rapid construction of multi-parameter phase diagrams from the local structure-function correlations observed at the sub-micron pixel scale.
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All authors Srinivas V. Mandyam, Esther Wang, Zhipan Wang, Bijuan Chen, Nishan C. Jayarama, Anmay Gupta, Eric A. Riesel, Valery I. Levitas, Christopher R. Laumann, Norman Y. Yao
Materials Science · Cross-listed from cond-mat.str-el
Charge order through crystallization of Frenkel excitons: realization in kagome metals
Ruoshi Jiang, Bartomeu Monserrat and Wei Ku
Charge order is a widely observed and representative example of spontaneous broken
symmetries in
quantum states of matter. Owing to the large intra-atomic Coulomb energy, the charge redistribution in such an order typically implies significant alteration of the electronic and
lattice properties of materials. While the standard description of charge order, namely a "charge density wave" instability of the
Fermi surface, has been broadly and successfully applied to good metals, its applicability to correlated ionic materials has been rather limited. Here, we propose an alternative general scenario of charge order - crystallization of long-lived Frenkel
excitons - suitable for these ionic materials. We demonstrate this scenario on the recently discovered kagome
superconductors and successfully reproduce all the characteristics of experimental observations on both local charge correlations and long-range ordering. The proposed generic scenario offers a long-sought understanding of charge order applicable to modern correlated functional materials.
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Materials Science · Cross-listed from cs.LG
Transformers Discover Molecular Structure Without Graph Priors
Tobias Kreiman, Yutong Bai, Fadi Atieh et al. (+3 more)
Computational simulations play a central role in scientific discovery, and machine learning (ML) has emerged as a promising alternative to traditional physics-based modeling. However, scientific modeling requires physically meaningful predictions, raising a fundamental question for data-driven methods: to what extent can physical inductive biases-that is, prior assumptions about the structure of the physical world-emerge by learning from data alone? In this work, we study atomistic modeling, a representative field in the computational sciences where ML architectures have historically embedded strong physical inductive biases-such as
geometric locality and graph structure. We develop a systematic understanding of how physical patterns can alternatively be discovered directly from data by training a model without domain-specific priors, including any manually defined atomistic pairwise interactions. We find that the model autonomously recovers key physical structure, such as learned interatomic interaction strengths that mirror classical electrostatics and interaction cutoffs consistent with traditional physical models. We further demonstrate predictable neural scaling law behavior with increased data and compute, and find accuracy on certain metrics competitive with physics-informed architectures. Our results clarify the boundary between engineered inductive biases and learnable physical structure, suggesting that general-purpose architectures can serve as principled baselines for scientific modeling by learning fundamental physical structure directly from data.
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All authors Tobias Kreiman, Yutong Bai, Fadi Atieh, Elizabeth Weaver, Eric Qu, Aditi S. Krishnapriyan
Materials Science
Reversal of strain state in a Mott insulator thin film by controlling substrate morphology
Reetendra Singh, Abhishek Rakshit, Galit Atiya et al. (+3 more)
The V2O3 phase diagram contains two insulating phases and one metallic phase with different
lattice structures. The stability of these phases is very sensitive to pressure, offering a mechanism to tune phase transitions by inducing strain in thin films. The most studied source of strain is
lattice mismatch between the film and the substrate. In this work, however, we find that the film/substrate thermal expansion mismatch can be made to play a dominant role by modifying the substrate morphology. When grown on sapphire, the
lattice mismatch induces compressive strain in the V2O3 films, whereas thermal expansion mismatch induces tensile strain. We find that minute changes in substrate morphology may relax the compressive strain component, allowing the thermally-induced tensile component to overcome it. Thus, by simple annealing of the substrates to create either a flat or stepped morphology, strongly compressive or tensile strains may be induced in the films. This results in either full suppression of the metal-
insulator transition or stabilization of insulating phases at all temperatures, exhibiting many orders of magnitude differences in film resistivity. To elucidate the strain relaxation mechanism, we use high-resolution scanning transmission electron microscopy (HRSTEM) to image the atomic steps in the substrate and the adjacent crystallographic defects in the V2O3. These findings offer a hitherto underexplored mechanism to tune strain in thin films, deepen our understanding of the effects of structural degrees of freedom on phase stability of a canonical Mott
insulator and may allow for applications requiring
insulator-metal switching above room temperature.
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All authors Reetendra Singh, Abhishek Rakshit, Galit Atiya, Michael Kalina, Yaron Kauffmann, Yoav Kalcheim
Materials Science · Cross-listed from cond-mat.mes-hall
Emergent Hierarchy in Localized States of Organic Quantum Chains
L. L. Lage, A. B. Félix, D. S. Gomes et al. (+2 more)
Organic
Quantum Chains (OQCs) represent a newly synthesized class of carbon-based nanostructures whose quasi-one-dimensional nature gives rise to unconventional electronic and transport phenomena. Here we investigate the electronic and transport properties of recently synthesized OQCs [Nature Communications, 12, 5895 (2021)]. Structural stability was first assessed through molecular dynamics relaxation combined with density functional theory (DFT). The optimized coordinates are then used in a tight-binding model with exponentially decaying hopping parameterization, which reproduces the DFT results with high accuracy. Our calculations reveal a robust and nearly constant energy gap across several OQC configurations, in agreement with experimental data. We also identify emergent hierarchical states, characterized by distinct localization behaviors within sets of localized bands. Finally, we analyze different transport responses in scenarios involving the one-dimensional OQC coupled to carbon corrals, as observed in the experimental data, highlighting their potential as promising systems for application in carbon nanodevices.
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All authors L. L. Lage, A. B. Félix, D. S. Gomes, M. L. Pereira Jr., A. Latgé
Materials Science · Cross-listed from cond-mat.mes-hall
Phonon Spin Selective One-Way Axial Phonon Transport in Chiral Nanohelix
Jia Li, Yu-Tao Tan, Yizhou Liu et al. (+1 more)
Selectively exciting and manipulating
phonons at nanoscale becomes more and more important but still remains challenging in modern nano-energy control and information sensing. Here, we show that the
phonon spin angular momentum provides an extra degree of freedom to achieve versatile manipulation of axial
phonons in nanomaterials via coupling to spinful multi-physical fields, such as circularly polarized infrared absorption. In particular, we demonstrate the nanoscale one-way axial
phonon excitation and routing in
chiral nanomaterials, by converting the
photon spin in circularly polarized optical fields into the collective interference
phonon spin. As exemplified in the smallest
chiral carbon nanotube, we show that the rectification rate can reach nearly 100%, achieving an ideal one-way
phonon router, which is verified by molecular dynamics simulations. Our results shed new light on the flexible
phonon manipulation via
phonon spin degree of freedom, paving the way for future
spin phononics.
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All authors Jia Li, Yu-Tao Tan, Yizhou Liu, Jie Ren
Materials Science · Cross-listed from cs.LG
Catalyst GFlowNet for electrocatalyst design: A hydrogen evolution reaction case study
Lena Podina, Christina Humer, Alexandre Duval et al. (+7 more)
Efficient and inexpensive energy storage is essential for accelerating the adoption of renewable energy and ensuring a stable supply, despite fluctuations in sources such as wind and
solar. Electrocatalysts play a key role in hydrogen energy storage (HES), allowing the energy to be stored as hydrogen. However, the development of affordable and high-performance catalysts for this process remains a significant challenge. We introduce Catalyst GFlowNet, a generative model that leverages machine learning-based predictors of formation and adsorption energy to design
crystal surfaces that act as efficient catalysts. We demonstrate the performance of the model through a proof-of-concept application to the hydrogen
evolution reaction, a key reaction in HES, for which we successfully identified platinum as the most efficient known catalyst. In future work, we aim to extend this approach to the oxygen
evolution reaction, where current optimal catalysts are expensive metal
oxides, and open the search space to discover new materials. This generative modeling framework offers a promising pathway for accelerating the search for novel and efficient catalysts.
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All authors Lena Podina, Christina Humer, Alexandre Duval, Victor Schmidt, Ali Ramlaoui, Shahana Chatterjee, Yoshua Bengio, Alex Hernandez-Garcia, David Rolnick, Félix Therrien
Materials Science
-Quantum Effects or Theoretical Artifacts? A Computational Reanalysis of Hydrogen's High-Pressure Phase Stability and Properties
Stefano Racioppi and Eva Zurek
Experimental and theoretical studies of the high-pressure phases of hydrogen are highly sensitive to methodological choices. We compare the cold phase diagram of hydrogen calculated between 400-700 GPa with meta-GGA functionals (R2SCAN and SCAN0) with the commonly employed GGA-PBE functional. Molecular phases are stabilized over the atomic phase to higher pressures with the meta-GGA, in closer agreement with
diffusion Monte Carlo calculations. R2SCAN
phonon spectra show that the dynamical instabilities and anharmonic signatures predicted at the GGA level vanish, indicating that such effects may partly arise from functional deficiencies rather than
quantum nuclear effects. Bonding analysis reveals that PBE artificially weakens intramolecular H-H bonds and enhances intermolecular interactions through charge delocalization, whereas meta-GGA preserves a more localized molecular character.
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Materials Science · Cross-listed from cond-mat.mes-hall
Electrically tunable ultrafast dynamics and interactions of hybrid excitons in a 2D semiconductor bilayer
Edoardo Lopriore, Charalambos Louca, Armando Genco et al. (+12 more)
Extended efforts have been devoted to the study of strongly-interacting
excitons and their dynamics, towards macroscopic
quantum states of matter such as Bose-Einstein condensates of
excitons and polaritons. Momentum-direct layer-hybridized
excitons in transition metal dichalcogenides have attracted considerable
attention due to their high oscillator strength and dipolar nature. However, the tunability of their interactions and dynamics remains unexplored. Here, we achieve an unprecedented control over the nonlinear properties of dipolar layer-hybridized
excitons in an electrically gated van der Waals homobilayer monitored by transient optical spectroscopy. By applying a vertical electric field, we reveal strong Coulomb interactions of dipolar hybrid
excitons, leading to opposite density-dependent energy shifts of the two main hybrid species based on their dipolar orientation, together with a strongly enhanced optical saturation of their absorption. Furthermore, by electrically tuning the interlayer tunneling between the hybridized carriers, we significantly extend the formation time of hybrid
excitons, while simultaneously increasing their decay times. Our findings have implications for the search on
quantum blockade and condensation of
excitons and dipolaritons in two-dimensional materials.
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All authors Edoardo Lopriore, Charalambos Louca, Armando Genco, Irantzu Landa, Daniel Erkensten, Charles J. Sayers, Samuel Brem, Raul Perea-Causin, Kenji Watanabe, Takashi Taniguchi, Christoph Gadermaier, Ermin Malic, Giulio Cerullo, Stefano Dal Conte, Andras Kis
Materials Science
Spin-phonon coupling and isotope-related pseudo-molecule vibrations in layered Cr$_2$Ge$_2$Te$_6$ ferromagnet
Grzegorz Krasucki, Katarzyna Olkowska-Pucko, Tomasz Woźniak et al. (+4 more)
The vibrational structure of chromium germanium telluride (Cr$_2$Ge$_2$Te$_6$, CGT) is investigated and a strong
spin-
phonon coupling is revealed. The measured high-resolution Raman scattering (RS) spectra are composed of the 10 Raman-active modes: 5A$_\textrm{g}$ and 5E$_\textrm{g}$, predicted by calculation using the density functional theory and identified using polarization-resolved RS measurements. We also studied the effect of temperature on the RS spectra of CGT from 5~K to 300~K. A strong magneto-
phonon coupling in CGT is revealed at temperatures of about 150~K and 60~K, which are associated with the appearance of the local
magnetic order in the material and the transition to the complete
ferromagnetic phase, respectively. Moreover, a unique shape of the A$_g^5$ mode composed of a set of very narrow Raman peaks is simulated using a model that takes into account vibrations of Ge-Ge pseudo-molecules for various Ge isotopes.
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All authors Grzegorz Krasucki, Katarzyna Olkowska-Pucko, Tomasz Woźniak, Mihai I. Sturza, Holger Kohlmann, Adam Babiński, Maciej R. Molas
Materials Science
Enhancing the Efficiency of Time-Dependent Density Functional Theory Calculations of Dynamic Response Properties
Zhandos A. Moldabekov, Sebastian Schwalbe, Uwe Hernandez Acosta et al. (+4 more)
X-ray Thomson scattering (XRTS) constitutes an essential technique for diagnosing material properties under extreme conditions, such as high pressures and intense
laser heating. Time-dependent density functional theory (TDDFT) is one of the most accurate available ab initio methods for modeling XRTS spectra, as well as a host of other dynamic material properties. However, strong thermal excitations, along with the need to account for variations in temperature and density as well as the finite size of the detector significantly increase the computational cost of TDDFT simulations compared to ambient conditions. In this work, we present a broadly applicable method for optimizing and enhancing the efficiency of TDDFT calculations. Our approach is based on a one-to-one mapping between the dynamic structure factor and the imaginary time density–density correlation function, which naturally emerges in Feynman's path integral formulation of
quantum many-body theory. Specifically, we combine rigorous convergence tests in the imaginary time domain with a constraints-based attenuation of narrow-band fluctuations to improve the efficiency of TDDFT modeling without the introduction of any significant bias. As a result, we can report a speed-up by up to an order of magnitude, thus substantially reducing the burden of computational cost required for XRTS analysis.
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All authors Zhandos A. Moldabekov, Sebastian Schwalbe, Uwe Hernandez Acosta, Thomas Gawne, Jan Vorberger, Michele Pavanello, Tobias Dornheim
Materials Science
A General-Purpose and Efficient Machine-Learned Potential for SiC from Ambient to Extreme Environments
Jintong Wu, Zhuang Shao, Junlei Zhao et al. (+5 more)
Silicon carbide (SiC) polymorphs are widely employed as
nuclear materials, mechanical components, and wide-bandgap
semiconductors. The rapid advancement of SiC-based applications has been complemented by computational modeling studies, including both ab initio and classical atomistic approaches. In this work, we develop a computationally efficient, general-purpose machine-learned interatomic potential (ML-IAP) capable of multimillion-atom molecular dynamics simulations over microsecond timescales. Using the ML-IAP, we map a broad pressure-temperature phase diagram and the threshold displacement energy distributions for the 2H and 3C polymorphs. Across a
benchmark covering conditions from ambient to extreme, including high-pressure/high-temperature states and high-energy cascade damage, tabGAP provides a favorable balance of accuracy, robustness, transferability, and computational cost among the tested empirical and ML-IAPs.
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All authors Jintong Wu, Zhuang Shao, Junlei Zhao, Flyura Djurabekova, Kai Nordlund, Fredric Granberg, Qingmin Zhang, and Jesper Byggmästar
Materials Science
Machine-learning-enabled methodology for the ab-initio simulations of sub-$\mu$m-wide nanoribbons
Guan-Hao Peng, Chin-Jui Huang, Wen-Teng Yang et al. (+1 more)
Simulation of mesoscopic nanostructures is a central challenge in condensed matter physics and device applications. First-principles methods provide accurate electronic structures but are computationally prohibitive for large systems, while empirical band theories are efficient yet limited by parameter fitting that neglects wavefunction information and often yields non-transferable parameters. We propose a methodology that bridges these approaches, achieving first-principles-level reliability with computational efficiency through a machine-learning-enabled tight-binding framework. Our approach starts with Wannier tight-binding (WTB) parameters from small nanostructures, which serve as training data for machine learning (ML). To remove the gauge freedom of Wannier functions that obscures size- and geometry-dependent parameter trends, we construct gauge-independent (GI) bases and transform the WTB model into a gauge-independent WTB (GI-WTB) model. This enables robust parameter fitting and ML prediction of parameter variations, yielding the machine-learning GI-WTB (ML-GI-WTB) model. Applied to MoS2 armchair-edge nanoribbons, the ML-GI-WTB model shows excellent agreement with first-principles results and enables reliable simulations of sub-$\mu$m-wide nanoribbons. This framework provides a scalable tool for predicting electronic properties of realistic nanostructures beyond the reach of conventional first-principles methods.
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All authors Guan-Hao Peng, Chin-Jui Huang, Wen-Teng Yang, Shun-Jen Cheng
Materials Science · Cross-listed from cond-mat.mes-hall
Tunable Wigner Molecules in a Germanium Quantum Dot
Chenggang Yang, Jun Lu, Hongzhang Wang et al. (+7 more)
The interplay between Coulomb interactions and kinetic energy underlies many exotic phases in condensed matter physics. In a two-dimensional electronic system, If Coulomb interaction dominates over kinetic energy, electrons condense into a crystalline phase which is referred as Wigner
crystal. This ordered state manifests as Wigner molecule for few electrons at the microscopic scale. Observation of Wigner molecules has been reported in
quantum dot and moire superlattice systems. Here we demonstrate hole Wigner molecules can be formed in a gate-defined germanium
quantum dot with high tunability. By varying voltages applied to the
quantum dot device, we can precisely tune the hole density by either changing the hole occupancy or the
quantum dot size. For densities smaller than a certain critical value, Coulomb interaction localizes individual holes into ordered
lattice sites, forming a Wigner molecule. By increasing the densities, melting process from a Wigner molecule to
Fermi liquid-like particles is observed. An intermediate configuration which indicates the coexistence of ordered structure and disordered structure can be formed within a narrow effective density range. Our results provide a new platform for further exploration of the microscopic feature of strong correlated physics and open an avenue to exploit the application of Wigner molecules for
quantum information in a very promising
spin qubit platform.
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All authors Chenggang Yang, Jun Lu, Hongzhang Wang, Jian Zeng, Wendong Bian, Zhengshan Guo, Jiankun Li, Yulei Zhang, Junwei Luo, Tian Pei
Materials Science
Metallurgy at the nanoscale: domain walls in nanoalloys
Grégoire Breyton, Hakim Amara, Jaysen Nelayah et al. (+8 more)
In binary
alloys, domain walls play a central role not only on the phase transitions but also on their physical properties and were at the heart of the 70's metallurgy research. Whereas it can be predicted, with simple physics arguments, that such domain walls cannot exist at the nanometer scale due to the typical lengths of the statistical fluctuations of the order parameter, here we show, with both experimental and numerical approaches how orientational domain walls are formed in CuAu nanoparticles binary model systems. We demonstrate that the formation of domains in larger NPs is driven by elastic strain relaxation which is not needed in smaller NPs where surface effects dominate. Finally, we show how the multivariants NPs tend to form an isotropic material through a continuous model of elasticity.
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All authors Grégoire Breyton, Hakim Amara, Jaysen Nelayah, Christine Mottet, Riccardo Gatti, Jérôme Creuze, Adrien Moncomble, Damien Alloyeau, Nathaly Ortiz Peña, Guillaume Wang, Christian Ricolleau
Materials Science
Giant enhancement of terahertz high-harmonic generation by cavity engineering of a three-dimensional Dirac semimetal
Siyu Duan, Lili Shi, Patrick Pilch et al. (+7 more)
We report on time-resolved ultrafast terahertz high-harmonic generation of strong field driven-dynamics of many-body Dirac
fermions. We demonstrate an experimental realization of near saturation regime of the high-order nonlinear responses with a
giant enhancement of terahertz third- and fifth-order harmonic yields by cavity-engineering a three-dimensional Dirac semimetal Cd3As2. By fabricating a designed structure of metasurface microcavities on a nanometer Cd3As2 thin film, we significantly enhance the near-field intensity of a picosecond terahertz excitation pulse in resonance with the microcavity eigenmode. The strong terahertz field drives the far-from-
equilibrium Dirac
fermions deeply into a nonperturbative regime, leading to the observation of near-saturation high-harmonic emission. Our experimental results confirm the predictions by Boltzmann transport theory, and substantiate a field-driven kinetic description of the strong nonthermal nonlinearity at the terahertz frequencies.
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All authors Siyu Duan, Lili Shi, Patrick Pilch, Anneke Reinold, Sergey Kovalev, Renato M. A. Dantas, Yunkun Yang, Faxian Xiu, Miriam Serena Vitiello, Zhe Wang
Materials Science · Cross-listed from cond-mat.mes-hall
Orbital Magnetization of Correlated States in Twisted Bilayer Transition Metal Dichalcogenides
Xiaoyu Liu, Chong Wang, Haoran Chen et al. (+3 more)
Recent observations of
quantum anomalous
Hall effects in moiré systems have revealed the emergence of interaction-driven ferromagnetism with significant orbital contributions. To capture this physics, we extend the modern theory of orbital magnetization to Hartree-Fock states and show that the standard expression remains valid with Hartree-Fock orbitals and
Hamiltonians. We then
benchmark our theory against the Kane-Mele-Hubbard model in a weak field, which yields excellent agreement with direct numerical calculations. Applying our theory to twisted MoTe$_2$
bilayers, we find orbital magnetization of order one Bohr magneton per moiré
cell with a non-monotonic twist-angle dependence. Our work establishes a general theory of orbital magnetization in interacting moiré systems and provides quantitative guidance for interpreting recent experiments.
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All authors Xiaoyu Liu, Chong Wang, Haoran Chen, Xiao-Wei Zhang, Ting Cao, Di Xiao
Materials Science
Multifunctional Oxide Nanosheets: Frictional, Hall, and Piezoelectric Deformation of 2D Ga2O3
Md Akibul Islam, Uichang Jeong, Nima Barri et al. (+4 more)
Atomically thin
oxides are increasingly recognized as an emerging class of 2D materials, yet their multifunctional properties have been far less investigated compared to other layered materials. Among these, gallium
oxide is distinguished by its ultrawide bandgap, thermal stability, and mechanical
rigidity, positioning it as a candidate material for nanoelectromechanical systems. In this study, the tribological, transport, and electromechanical properties of beta-Ga2O3 nanosheets were probed using atomic force microscopy (AFM)–based techniques. Friction force microscopy (FFM) was used to investigate interfacial sliding, and a dependence of friction on external bias was observed, which was attributed to defect-mediated charge trapping. Van der Pauw
Hall measurements were conducted up to 400 $^{\circ}$C, through which the ultrawide bandgap nature of beta-Ga2O3 was confirmed, as electronic transport remained suppressed despite high thermal activation. Piezoresponse force microscopy (PFM) was further applied, and a measurable converse electromechanical response on the order of a few pm/V was revealed, consistent with oxygen-vacancy–induced
symmetry breaking. By integrating tribological, electrical, and electromechanical measurements, it was demonstrated that beta-Ga2O3 nanosheets present a unique platform in which insulating stability, bias-tunable interfacial mechanics, and defect-enabled electromechanical activity coexist, offering new opportunities for multifunctional
oxide nanodevices.
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All authors Md Akibul Islam, Uichang Jeong, Nima Barri, Azmeera Jannat, Ali Zavabeti, Seungbum Hong, Tobin Filleter
Materials Science · Cross-listed from cond-mat.supr-con
Re-entrant superconductivity at an oxide heterointerface
D. Maryenko, M. Kawamura, I. V. Maznichenko et al. (+7 more)
A
magnetic field typically suppresses superconductivity by either breaking Cooper pairs via the Zeeman effect or inducing
vortex formation. However, under certain circumstances, a
magnetic field can stabilize superconductivity instead. This seemingly counterintuitive phenomenon is associated with
magnetic interactions and has been extensively studied in three-dimensional materials. By contrast, this phenomenon, hinting at unconventional superconductivity, remains largely unexplored in two-dimensional systems, with moiré-patterned
graphene being the only known example. Here, we report the observation of re-entrant superconductivity (RSC) at the epitaxial (110)-oriented LaTiO3-KTaO3 interface. This phenomenon occurs across a wide range of charge carrier densities, which, unlike in three-dimensional materials, can be tuned in-situ via electrostatic gating. We attribute the re-entrant superconductivity to the interplay between a strong
spin-orbit coupling and a
magnetic-field driven modification of the
Fermi surface. Our findings offer new insights into re-entrant superconductivity and establish a robust platform for exploring novel effects in two-dimensional
superconductors.
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All authors D. Maryenko, M. Kawamura, I. V. Maznichenko, S. Ostanin, D. Zhang, M. Kriener, V. K. Dugaev, E. Ya. Sherman, A. Ernst, M. Kawasaki
Materials Science · Cross-listed from cs.LG
Securing generative artificial intelligence with parallel magnetic tunnel junction true randomness
Youwei Bao, Shuhan Yang and Hyunsoo Yang
Deterministic pseudo random number generators (PRNGs) used in generative artificial intelligence (GAI) models produce predictable patterns vulnerable to exploitation by attackers. Conventional defences against the vulnerabilities often come with significant energy and latency overhead. Here, we embed hardware-generated true random bits from
spin-transfer torque
magnetic tunnel junctions (STT-MTJs) to address the challenges. A highly parallel, FPGA-assisted prototype computing system delivers megabit-per-second true random numbers, passing NIST randomness tests after in-situ operations with minimal overhead. Integrating the hardware random bits into a generative
adversarial network (GAN) trained on CIFAR-10 reduces insecure outputs by up to 18.6 times compared to the low-quality random number generators (RNG) baseline. With nanosecond switching speed, high energy efficiency, and established scalability, our STT-MTJ-based system holds the potential to scale beyond 106 parallel
cells, achieving gigabit-per-second throughput suitable for large
language model sampling. This advancement highlights spintronic RNGs as practical security components for next-generation GAI systems.
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Materials Science
Electride behavior at high pressure in silicon and other elements in solid and liquid phases
Salma Ahmed, Felipe González-Cataldo, Victor Naden Robinson et al. (+1 more)
Electrides are materials in which some of the electrons are localized at the interstitial sites rather than around the atoms or along atomic bonds. Most elemental electrides are either alkali metals or alkaline-earth metals because of their low ionization potential. In this work, we report that elemental silicon becomes an electride at pressures exceeding 400 GPa. With ab initio molecular dynamics (MD) simulations, we study this behavior for silicon, sodium, potassium, and magnesium at high pressure and temperature. We performed simulations for
liquids and ten
crystal structures. Charge density and electron localization functions (ELF) are analyzed for representative configurations extracted from the MD trajectories. By analyzing a variety of electride structures, we suggest the following quantitative thresholds for the ELF and charge density in each interstitial site to classify high-pressure electrides: (1) the maximum ELF value should be greater than 0.7, (2) there should be at least 0.9 electrons near the ELF basin, and (3) the
Laplacian charge density, $\nabla^2 \rho(\mathbf{r}_0)$, should be negative with magnitude greater than $10^{-3}\ e/\mathrm{bohr}^5$. Finally, we compute X-ray diffraction patterns to determine the degree to which they are affected by the electride formation. Overall, this framework could become a
benchmark for future theoretical and experimental studies on electrides.
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All authors Salma Ahmed, Felipe González-Cataldo, Victor Naden Robinson, Burkhard Militzer
Materials Science
Obstruction-Driven Parity Inversion for Enhanced Optical Absorption in Hexagonal Transition Metal Dichalcogenides
Seungil Baek, Jun Jung and Yong-Hyun Kim
The optical selection rule states that opposite parity between the valence and conduction bands is required for optical absorption to occur. However, monolayer hexagonal transition metal dichalcogenides (h-TMDs) such as $ \mathrm{MoS}_{2} $ exhibit pronounced optical absorption despite their nominally dipole-forbidden d-d transitions. In this Letter, we elucidate a parity inversion mechanism through which obstruction-driven band inversion promotes dipole-allowed optical transitions near the band edge in monolayer h-TMDs. By comparing trivial and obstructed atomic limit phases, we show that intersite interactions between hybridized d orbitals induce parity inversion. Our results provide a novel approach to tuning optical properties through parity control, bridging the gap between
topology and light-matter interaction.
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