Materials Science · Cross-listed from physics.app-ph
AlN Gate Interlayer for UWBG AlGaN Transistors with Breakdown Field >6.9 MV/cm and PFOM >1.8 GW/cm2
Seungheon Shin, Jonathan Pratt, Joe McGlone et al. (+5 more)
We report the demonstration of regrown epitaxial AlN gate interlayers with ultra-wide bandgap (UWBG) AlGaN polarization-graded field effect transistors (PolFETs). The introduction of the epitaxial AlN gate interlayer enables significant improvement in breakdown strength, with average breakdown field exceeding 6.94 MV/cm, which represents state-of-the-art for lateral field effect transistors, while maintaining excellent on-state current density exceeding 1 A/mm. The integration of epitaxial AlN enables state-of-the-art power-switching figure of merit exceeding 1.87 GW/cm2 at a breakdown voltage exceeding 1.45 kV. This work shows the potential of UWBG AlGaN for next-generation high-power switching and RF applications with enhanced device performance established by a high-quality epitaxially regrown AlN gate interlayer.
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All authors Seungheon Shin, Jonathan Pratt, Joe McGlone, Yinxuan Zhu, Brianna A. Klein, Andrew Armstrong, Andrew A. Allerman, Siddharth Rajan
Materials Science · Cross-listed from cond-mat.mes-hall
Second-Order Synaptic Memory using Inherent Plasticity of Moiré Superlattices
Tanweer Ahmed, Kenji Watanabe, Takashi Taniguchi et al. (+2 more)
Achieving synaptic functionality electronically in a single-element
quantum material is a fundamental challenge, as conventional methods rely on the introduction of extrinsic charge-traps or polar components. Here, we demonstrate that twisted double
bilayer graphene (tDBLG) moiré superlattices, composed purely of carbon, exhibit electronic hysteresis and plasticity in presence of twist-angle disorder. Inversion
symmetry breaking at the moiré length scales also gives rise to second-order nonlinear electrical response via disorder-mediated extrinsic mechanisms. Such second-order nonlinearity is highly tunable in both sign and magnitude by varying carrier concentration and vertical displacement field. We harness the coexistence of electronic plasticity and second-order nonlinearity to realize a second-order synaptic
memory device. Our findings establish strained moiré carbon systems as a powerful new platform for energy-efficient neuromorphic computing, demonstrating that complex electronic functionality can emerge purely from
symmetry breaking physics in a single-element material.
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All authors Tanweer Ahmed, Kenji Watanabe, Takashi Taniguchi, Fèlix Casanova, Luis E. Hueso
Materials Science · Cross-listed from cond-mat.mes-hall
Negative temperature coefficient of Gilbert damping in magnetic bilayers
Lulu Cao, Yuting Gong, Xianyang Lu et al. (+5 more)
The Gilbert damping of
magnetic materials is an important
magnetic parameter that determines the switching speed and energy dissipation of spintronic devices. In simple metals, the intrinsic Gilbert damping increases with temperature and diverges near the Curie temperature as a result of
spin fluctuations. Here we present atomistic simulations and experimental measurements showing surprising and opposite behavior in Py/Nd
bilayers, where the Gilbert damping decreases with increasing temperature. The effect arises because of the enhanced damping at the interface as a result of
spin pumping, where elevated temperatures cause a dynamic separation of the interfacial and bulk magnetization during relaxation. Furthermore, the temperature dependence of the damping can be controlled by varying the thickness of the Nd capping layer. Our findings present a new spintronic effect that can be used to modify the dynamic properties of nanoscale materials and devices for enhanced energy efficiency or with improved switching dynamics.
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All authors Lulu Cao, Yuting Gong, Xianyang Lu, Yongbing Xu, Ya Zhai, Jing Wu, Roy W. Chantrell, Richard F. L. Evans
Materials Science
Shift current conductivity in monolayer SnS: a tight-binding analysis
Yuki Kusunoki, Tomoaki Kameda and Katsunori Wakabayashi
We investigate the bulk photovoltaic effect in monolayer SnS using an effective tight-binding model derived from first-principles calculations. By comparing short-range and long-range hopping models, we show that the essential features of the shift current conductivity are captured by a minimal model. The shift current is decomposed into transition intensity and shift vector, enabling identification of dominant interband transitions. The comparison reveals that long-range hopping processes quantitatively modify the peak positions and magnitudes, while the short-range model retains the characteristic low-energy structure of the nonlinear response. Our findings provide a transparent framework for understanding and designing bulk photovoltaic effects in two-dimensional materials.
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Materials Science
Optoelectronics and Magnetic properties calculation of RE$_2$MnNiO$_6$ (RE=La-Lu,Y) using Density Functional Theory
Debidutta Pradhan
RE$_2$MnNiO$_6$ (RE = La-Lu) family of ordered double-perovskite
oxides hosts a corner-sharing network of alternating NiO$_6$ and MnO$_6$ octahedra whose electronic and
magnetic ground states are systematically governed by the A-site ionic radius through the lanthanide contraction. The strong localisation of RE 4f electrons poses a fundamental challenge to density-functional treatments, yet the hybridisation between 4f and neighbouring 5d (RE) or 3d (Ni, Mn) states is central to the origin of exchange interactions and optoelectronic response across the series. We present a comprehensive first-principles study of the electronic structure,
lattice dynamics, and optical properties of representative RE2NiMnO6 compounds within the DFT+U framework. To disentangle the role of Kondo-type 4f-d hybridisation, calculations are performed with the RE 4f electrons treated both as frozen core states and explicitly in the valence
manifold, enabling a direct assessment of their contribution to the band structure, dielectric function, and
phonon dispersion.
Spin-polarised calculations reveal significant
spin-channel asymmetry, with
magnetic moments reaching up to 30 $\mu$B per formula unit for select members of the series. The results establish a unified picture of how 4f occupancy and octahedral distortion collectively determine the
magnetic and optoelectronic potential of this double-perovskite family.
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Materials Science · Cross-listed from cond-mat.supr-con
Anharmonic lattice dynamics and superconductivity in strained bulk and surface niobium
Mihir Ranjan Sahoo, Roman Lucrezi, Pedro Nunes Ferreira et al. (+5 more)
Using first-principles calculations, we investigate how homogeneous strain and crystallographic surface orientation modify the vibrational and superconducting properties of niobium. For bulk Nb, tensile strain strongly softens the
phonon spectrum and enhances the electron–
phonon coupling, increasing the superconducting transition temperature from 9.5 K at
equilibrium to 14.5 K at $\sim\!6\%$
lattice expansion. For the low-index Nb(001), Nb(110), and Nb(111) surfaces, harmonic
phonon calculations exhibit imaginary modes, showing that anharmonic
lattice effects are essential. To treat these effects efficiently, we train Nb-specific machine-learning interatomic potentials on bulk and slab first-principles configurations and use them to accelerate
stochastic self-consistent harmonic approximation calculations, thereby obtaining anharmonically renormalized
phonon modes that are combined with density-functional perturbation theory electron–
phonon matrix elements to construct the Eliashberg spectral function. Among the clean free-standing slabs considered here, Nb(001) exhibits the strongest electron–
phonon coupling and the highest calculated transition temperature of 10.0 K, while Nb(110) and Nb(111) show progressively reduced pairing strength. Finally, by analyzing the Eliashberg spectral function and the functional derivative $\delta T_\text{c}/\delta\alpha^2F(\omega)$, we identify the
phonon energy ranges most effective for superconducting pairing. Our results show that strain, surface termination, and anharmonic
phonon renormalization provide complementary and interrelated microscopic routes for tuning superconductivity in Nb.
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All authors Mihir Ranjan Sahoo, Roman Lucrezi, Pedro Nunes Ferreira, Chia-Nien Tsai, Matthew Julian, Rohit P. Prasankumar, Mahmoud I. Hussein, Christoph Heil
Materials Science · Cross-listed from cond-mat.dis-nn
Irregular Metamaterial Networks
Thomas P. Wytock, Chiara Daraio, Heinrich M. Jaeger et al. (+4 more)
Metamaterials can achieve exceptional functionality through careful engineering of their mesoscale structure. Although appropriately introduced irregularities can be advantageous, current approaches largely conform to regular structures to preserve tractability. Here, we contend that network theory, enriched with geometry and physics, provides a natural framework for designing metamaterials with controlled irregularities at relevant scales, thereby enabling the discovery of new property-enhancing structures. We examine how this augmented network theory can facilitate the creation of irregular metamaterials with enhanced or novel properties and how metamaterial research, in turn, is opening new directions in network science. Supported by machine learning and advanced self-assembly, the emerging field of irregular metamaterial networks is poised to transform inverse design and scalable manufacturing of novel materials.
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All authors Thomas P. Wytock, Chiara Daraio, Heinrich M. Jaeger, Christopher A. Schuh, Lorenzo Valdevit, Vincenzo Vitelli, Adilson E. Motter
Materials Science
Symmetry-Protected Weyl Nodal Loops in a Triangular Altermagnet
Chao-Chun Wei, Xiaoyin Li, Sophia Adams et al. (+9 more)
Weyl semimetals and altermagnets represent two distinct classes of
quantum materials exhibiting nontrivial topological and
magnetic order, respectively. Here we report the realization of a Weyl nodal-loop altermagnet in Cr$_7$Se$_8$, combining
neutron diffraction and first-principles calculations. The hexagonal system hosts a coplanar $120^\circ$ compensated
magnetic order on a triangular
lattice, which breaks inversion-time-reversal and translation-time-reversal
symmetries simultaneously while preserving a crystalline mirror plane. The resulting electronic structure features linearly dispersing nodal loops close to the
Fermi level ($E_F$) confined to the mirror-invariant $k_z=0$ plane. Along high-
symmetry directions, the crossings near $E_F$ form Dirac-like fourfold degeneracies in the absence of
spin-orbit coupling; at generic momenta, these crossings split into twofold and form continuous Weyl-like nodal loops protected by mirror
symmetry. The momentum-dependent
spin polarization exhibits an $f$-wave-like pattern characteristic of odd-parity altermagnets.
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All authors Chao-Chun Wei, Xiaoyin Li, Sophia Adams, Jacob Kjeldahl Jensen, Qiang Zhang, Jue Liu, Maxim Avdeev, Dinesh Kumar Yadav, Vikram V. Deshpande, Luisa Whittaker-Brooks, Feng Liu, Huiwen Ji
Materials Science
Towards Automated Discovery: A Review of Generative Models, Multimodal Learning and Closed-Loop Workflows in Inverse Materials Design
Anand Babu, Rogério Almeida Gouvêa and Gian-Marco Rignanese
Inverse materials design is shifting materials discovery from forward prediction toward targeted proposal of candidates that satisfy objectives under physical constraints. Here, we review advances in generative
crystal structure modeling,
multimodal learning, and closed-loop design pipelines for crystalline solids. We survey how generators learn chemical-structural priors from databases to enable controllable sampling of periodic structures, comparing variational autoencoders, normalizing flows, autoregressive models, and
diffusion models. Across these families, we examine where feasibility constraints and physical priors enter, from representations and training objectives to sampling-time guidance, screening, and relaxation. We also discuss
multimodal learning combining
crystal structures, thermodynamic and electronic information, microscopy, spectroscopy, processing context, and scientific text to construct materials representations. Inverse-design strategies integrating conditional generation with latent optimization,
Bayesian optimization, reinforcement learning, and active learning are also examined. We highlight recurring failure modes, including surrogate exploitation, diversity collapse, distribution shift, and the stability-synthesizability gap, and outline evaluation based on validity, novelty, uniqueness, stability, and cost. To support credible claims, we define a nine-rung discovery-credibility ladder and propose a minimum reporting standard: declared matching tolerances and database snapshots; separate reporting of uniqueness, training-set memorization, and external rediscovery; novelty as a continuous distance distribution; energy-above-hull distributions with functional and hull version; relaxation-survival and dynamical stability rates; and validation cost per credible hit. Headline validity or S.U.N. rates without these disclosures should be treated as uninformative.
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Materials Science
Hydrothermally-Assisted Sintering of Calcium Hydroxide Sputtering Targets: A Route to Quantum-Grade CaO Thin Films
Jake A. DeChiara, Tainara Coutinho, Saeed S.I. Almishal et al. (+1 more)
In this report we demonstrate dense polycrystalline calcium hydroxide ceramics fabricated by hydrothermally-assisted sintering - often referred to as cold-sintering - to produce high-purity calcium hydroxide targets for calcium
oxide thin film deposition. Calcium hydroxide ceramics exhibit up to 98% theoretical density without thermal dehydration, when sintered at temperatures between 100 {\deg}C - 300{\deg} C with 400 MPa applied uniaxial pressure for 1 hour. The brucite phase is preserved in calcium hydroxide targets at all temperatures. Small equivalent fractions of calcium carbonate are present in both the calcium hydroxide precursor powder and final targets suggesting minimal additional production during formation and densification. Microstructure
evolution during densification is documented by scanning electron microscopy, indicating both mass transport and plastic deformation densification mechanisms. The hydrothermal-assisted sintering process is scaled up to produce 2-inch diameter calcium hydroxide targets suitable for sputter deposition. We also report epitaxial calcium
oxide film deposition from these targets on r-plane sapphire substrates. (002) oriented epitaxial films are achieved with a time-stable 1.2 nm per minute deposition rate. We note that energetic bombardment during growth can be substantial at these rates even when 1 mol% oxygen is added to the sputtering process necessitating the low deposition rate conditions.
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All authors Jake A. DeChiara, Tainara Coutinho, Saeed S.I. Almishal, Jon-Paul Maria
Materials Science · Cross-listed from cs.LG
Speculative Sampling For Faster Molecular Dynamics
Arthur Kosmala, Stephan Günnemann, Meng Gao et al. (+1 more)
Molecular dynamics (MD) is a key tool for simulating the dynamical behavior of atomic systems. However, MD is inherently serial, which makes it difficult to increase single-system throughput with concurrent compute. To address this, we introduce Langevin Speculative Dynamics (LSD), a distributed and model-agnostic speculative sampler for accelerating MD without adding relative error. Inspired by speculative methods in
language and
diffusion modeling, LSD uses a draft model to propose fast simulation steps and verifies them in parallel with a slower target model, applying a transport map from the draft to the target distribution. We extend speculative sampling to second-order Langevin dynamics, derive the achievable speedup as a function of physical parameters, show that LSD generalizes across different systems and draft-target combinations with a 3-9x speedup, and confirm theoretically and empirically that LSD samples trajectories from its target model distribution.
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All authors Arthur Kosmala, Stephan Günnemann, Meng Gao, Brandon Wood
Materials Science · Cross-listed from cond-mat.str-el
Suppression of p-Wave Altermagnetism by Localized 4f Electrons in CeNiAsO
Jiuxiang Zhang, Yueyang Sun, Honglin Zhou et al. (+32 more)
Altermagnetism, characterized by momentum-dependent
spin splitting and zero net magnetization, has so far been explored mainly in weakly or moderately correlated d-electron systems. How
symmetry-allowed altermagnetic band splitting manifests in heavy-
fermion materials, where
magnetic exchange competes with Kondo correlations, remains unclear. Here we use high-resolution angle-resolved photoemission spectroscopy (ARPES) to investigate CeNiAsO, a Kondo-
lattice system that was predicted to be a candidate for p-wave altermagnetism.
Fermi surface mapping and polarization-dependent ARPES show that the experimentally observed itinerant bands are mainly derived from Ni 3d orbitals, while resonant photoemission reveals that the Ce 4f states remain predominantly localized with residual c-f hybridization. Ultra-low-temperature measurements reveal no resolvable near-
Fermi-level p-wave-like exchange splitting on the Ni 3d-derived conduction bands across the successive
antiferromagnetic transitions. These experimental observations cannot be captured by an itinerant-4f band-structure description, which predicts a sizable p-wave splitting in the itinerant bands. When the localized Ce 4f character is incorporated, our band structure calculations indicate that the itinerant Ce 4f band weight is shifted away from the
Fermi level and the p-wave-like splitting on the Ni 3d-derived bands is reduced to the few-meV scale. These results establish CeNiAsO as a strongly correlated f-electron setting in which the
magnetic symmetry allows p-wave-like band splitting, but localized 4f electrons strongly suppress its observable itinerant single-particle signature.
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All authors Jiuxiang Zhang, Yueyang Sun, Honglin Zhou, Jumin Shi, Di Wu, Hongze Gu, Wenjin Mao, Hengrui Dong, Yu Xu, Yinghao Li, Ziling Cao, Taimin Miao, Bo Liang, Neng Cai, Wenpei Zhu, Mingkai Xu, Jiaqi Chen, Chunhong Deng, Bo Liu, Xun Ma, Zhengtai Liu, Mao Ye, Shenjin Zhang, Zhimin Wang, Fengfeng Zhang, Feng Yang, Qinjun Peng, Zuyan Xu, Guodong Liu, Xintong Li, Hanqing Mao, Shiliang Li, Hongming Weng, Lin Zhao, X. J. Zhou
Materials Science · Cross-listed from cond-mat.str-el
Quenching of Nonrelativistic $p$-Wave Spin Splitting by Reduced $c\text{-}f$ Coupling in $\text{CeNiAsO}$
Xinnuo Zhang, Zhicheng Jiang, Shibo Shen et al. (+10 more)
The application of
spin-space group
symmetries to noncollinear antiferromagnets has led to the prediction of odd-parity, nonrelativistic
spin splittings, making the physical realization of a practical $p$-wave magnet a central pursuit in spintronics. The layered heavy-
fermion oxypnictide $\text{CeNiAsO}$ has been widely regarded as a prototypical platform to verify this paradigm. Here, we investigate the electronic structure of single-
crystal $\text{CeNiAsO}$ using high-resolution, ultra-low-temperature and resonant angle-resolved photoemission spectroscopy (ARPES), and $ab-initio$ calculations. Across the consecutive
magnetic transitions into the ordered phases, our spectroscopic data reveal neither the expected band folding associated with a
spin density wave nor any observable $p$-wave
spin splitting, demonstrating that the conduction bands retain full degeneracy. By tracking the temperature dependence of the Ce 4$f$ spectral weight via resonant ARPES, we find negligible $c\text{-}f$ hybridization near the
Fermi level within magnetically ordered states, confirming that the Ce 4$f$ electrons reside close to the localized limit. Our findings establish a clear many-body constraint on the projection of real-space
magnetic symmetries onto momentum-space electronic bands, demonstrating that
symmetry classifications constitute a necessary framework but are not a sufficient condition for nonrelativistic
spin splittings in the presence of strong electronic correlations.
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All authors Xinnuo Zhang, Zhicheng Jiang, Shibo Shen, Jian Yuan, Junseo Yoo, Xun Ma, Mao Ye, Jishan Liu, Zhengtai Liu, Changyoung Kim, Yanfeng Guo, Yilin Wang, Dawei Shen
Materials Science · Cross-listed from physics.chem-ph
DPA4: Pushing the Accuracy-Cost Frontier of Interatomic Potentials with EMFA SO(2) Convolution
Tiancheng Li, Wentao Li, Anyang Peng et al. (+4 more)
Machine-learning interatomic potentials now approach
quantum-mechanical accuracy, but the most expressive equivariant architectures are costly to evaluate, and the leading ones depend on auxiliary denoising or direct-force pretraining. We introduce DPA4, an SE(3)-equivariant architecture spanning six size classes from 0.48 to 25 million parameters and reaching the accuracy of the strongest published models at several-fold to an order-of-magnitude higher inference throughput. Its convolution couples edge and node features across all angular degrees in an edge-local frame, and its Wigner bilinear nonlinearity is universal in its full form and, on an exact quadrature grid, equivariant to machine precision. On Matbench Discovery, DPA4 leads every ranked metric, and every variant evaluated lies on the accuracy–throughput Pareto frontier of the compliant leaderboard. DPA4-Pro attains the lowest energy error on OMat24 and lower total-energy and force errors than the strongest conservative baseline on the OMol25 composition-validation split. All variants are trained through the conservative energy-gradient path alone, made practical by a threefold-faster compiled implementation. DPA4 thus brings leaderboard-class accuracy within the routine compute budgets of molecular-dynamics and materials-screening workflows, for both inorganic
crystals and organic molecules.
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All authors Tiancheng Li, Wentao Li, Anyang Peng, Jianming Xue, Linfeng Zhang, Duo Zhang, Han Wang
Materials Science · Cross-listed from quant-ph
Optical Stability and Photophysics of NV Centers in Diamond up to 120 GPa
Kin On Ho, Cassandra Dailledouze, Vytautas Žalandauskas et al. (+9 more)
The nitrogen vacancy (NV) center has emerged as a powerful
quantum sensor in high-pressure research, with the observation of optically detected
magnetic resonance at megabar pressures. However, some aspects of NV physics require further investigation to optimize the development of NV-based sensing under pressure. Here, we study both experimentally and theoretically the optical properties of the NV center under hydrostatic pressure. We investigate the
evolution of the zero-
phonon line (ZPL) position, radiative lifetimes, optical lineshapes, and photoionization thresholds of the NV center under pressures up to ~120 GPa. We also provide spectroscopic guidelines for performing high-pressure optical experiments. Our results confirm that the NV center remains a robust
quantum sensor under extreme hydrostatic pressures, especially for
magnetic characterization.
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All authors Kin On Ho, Cassandra Dailledouze, Vytautas Žalandauskas, Grégoire Le Caruyer, Marek Maciaszek, Claire Roussy, Marie-Pierre Adam, Martin Schmidt, Loïc Toraille, Paul Loubeyre, Lukas Razinkovas, Jean-François Roch
Materials Science
Universal theory of domain-wall width in multi-sublattice Heisenberg magnets
José M. Lendínez, Marta Yanguas, Theodor Griepe et al. (+4 more)
We propose a universal expression for the domain-wall width in generic multi-sublattice Heisenberg magnets, applicable to ferro-, antiferro-, and ferrimagnetic orders. The result follows from an exact connection between the domain-wall profile and the long-wavelength
spin-wave dispersion, yielding a unified framework for describing
magnetic textures across distinct ordering types. The predictions show excellent quantitative agreement with large-scale atomistic
spin dynamics simulations over a broad range of exchange and anisotropy values and
spin multi-sublattice structures, including three-dimensional rock-salt-type magnets and two-dimensional honeycomb and kagome ferromagnets. Moreover, we establish a general microscopic foundation for the temperature dependence of the domain-wall width. Our approach offers a powerful tool for understanding domain-wall profiles in complex
spin systems.
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All authors José M. Lendínez, Marta Yanguas, Theodor Griepe, Michael Saur, Rubén M. Otxoa, Levente Rózsa, Unai Atxitia
Materials Science
Layer-Resolved Nonlinear Optics in Finite-Thickness Two-Dimensional Systems
Liangting Ye, Chengzhi Wu, Zeyu Jiang et al. (+1 more)
Nonlinear optical (NLO) responses in two-dimensional
quantum-confined systems are typically described within bulk-based frameworks as macroscopic spatial averages. In finite-thickness van der Waals multilayers directly relevant to nanoscale devices, this picture substantially breaks down. Here, we establish a general
symmetry-based framework for classifying second-order NLO responses in multilayers. We reveal a layer-resolved organization into skin, weak-skin, and hidden effects governed by local
symmetry and stacking order. First-principles calculations for both nonmagnetic and
spin-polarized systems confirm our predictions, demonstrating that stacking alone suffices to dramatically reshape both the spatial pattern and magnitude of the NLO response, a phenomenon not explainable within standard bulk theory. Our results establish stacking geometry as an effective knob for engineering surface-selective NLO responses in layered materials.
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All authors Liangting Ye, Chengzhi Wu, Zeyu Jiang, Bing Huang
Materials Science · Cross-listed from cond-mat.mes-hall
Ferroelectric hysteresis in singly aligned graphene-hBN moiré superlattices
Bao Q. Tu, Tanweer Ahmed, Garen Avedissian et al. (+7 more)
Ferroelectric materials have the unique ability to maintain an electric polarization which can be reversed under an external applied electric field. This property makes them valuable for applications such as non-volatile random-access
memories, transducers, actuators and electro optic modulators. Recently, emergent unconventional ferroelectricity has been demonstrated in moiré superlattices of
bilayer graphene and hexagonal boron nitride (hBN) hosting non centrosymmetric stacking order. Whether this phenomenon is also present in noncentrosymmetric single layer
graphene (SLG)-hBN moiré superlattices is still under debate. Here we demonstrate a ferroelectric response in an SLG-hBN moiré superlattice. Through
Hall measurements, we pinpoint the origin of the hysteretic behavior to abnormal charge screening due to the moiré superlattice band and estimate the spontaneous polarization magnitude in the moiré superlattice structure. Temperature dependent measurements confirm that the hysteretic behavior persists from 2K up to room temperature, opening opportunities for high-mobility, ultrathin non-volatile devices
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All authors Bao Q. Tu, Tanweer Ahmed, Garen Avedissian, Suzanne Lancaster, Mayank Sharma, Kenji Watanabe, Takashi Taniguchi, Fèlix Casanova, Marco Gobbi, Luis E. Hueso
Materials Science
Neural Spectral Element Methods for stiff multiphysics PDEs with electrochemical transport benchmarks
Conrard Giresse Tetsassi Feugmo and David Pankaczy
The Neural Spectral Element Method (NSEM) evaluates each network only at fixed Legendre-Gauss-Lobatto quadrature nodes and replaces all derivative calls with precomputed spectral differentiation
matrices. The resulting deterministic loss enables limited-
memory BFGS (L-BFGS) to reach residuals of 10^-9 to 10^-10. A Kosloff-Tal-Ezer coordinate map resolves electrochemical boundary layers, while a mesh-free neural mortar framework couples multi-element domains. On the four-example Poisson-Nernst-Planck (PNP)
benchmark of Huang and co-workers, NSEM attains 10^-4 to 10^-7 relative pointwise error with two orders of magnitude fewer collocation points than the adaptive-resampling PINN baseline. Both a tanh multilayer perceptron (MLP) and a basis-aligned Legendre Kolmogorov-Arnold Network (KAN) backbone attain spectral accuracy within the same NSEM infrastructure, with the KAN requiring roughly half the Adam steps to enter the L-BFGS basin of attraction on the 1D PNP
benchmark.
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Materials Science
Surface Modification for III-V Selective Area Molecular Beam Epitaxy of Non-Selective Mask Materials
Ashlee M. García, Byron D. Aguilar, William J. Doyle et al. (+4 more)
Selective-area embedded regrowth of III-V
semiconductors by molecular beam epitaxy enables the seamless integration of metals and dielectrics into crystalline material for novel design of optoelectronic devices. However, traditional masks like $SiO_2$ and $Si_{3}N_{4}$ limit the design of high-contrast photonics in the infrared due to their high extinction coefficients at technologically relevant wavelengths. Consequently, there is a need to explore alternative mask materials to expand the selective area molecular beam epitaxy capabilities beyond those traditionally used. This study evaluates the deposition selectivity of the alternative materials $Al_{2}O_{3}$, $TiO_2$, and $HfO_2$, films with preferable spectral responses but higher surface reactivity. It was found that $Al_{2}O_{3}$ exhibits promising selective growth characteristics within typical GaAs growth temperatures, $HfO_2$ demonstrated a high non-selectivity dominated by Ga adsorption on the mask at temperatures up to 650 $^\circ$C, and $TiO_2$ proved reactive during deposition. To achieve selective growth of highly non-selective and even reactive mask materials, a surface modification technique was employed to improve the selective growth characteristics of any given film. Selective growth of $Si_{3}N_{4}$ and $TiO_2$ films was achieved with the application of a thin $SiO_2$ capping layer utilizing growth conditions typical of the GaAs/$SiO_2$ system. The relationship between the thickness of $SiO_2$ caps and growth selectivity was examined, revealing that sub-1 nm capping layers can significantly influence the mask surface chemistry, indicating that by depositing a thin layer of $SiO_2$, $SiO_2$-like selectivity for any mask material can be realized without degrading its optical response.
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All authors Ashlee M. García, Byron D. Aguilar, William J. Doyle, Pernille Undrum Fathi, Federico Capasso, Daniel Wasserman, Seth R. Bank
Materials Science
Room-Temperature Electric-Field Control of Anomalous Hall Effect in Py/BTO/LSMO Heterostructures
Kusampal Yadav, Kousik Das, Aditya Raj et al. (+7 more)
We demonstrate room temperature electric field control of the anomalous
Hall effect in epitaxial Ni80Fe20 (Py) BaTiO3 (BTO) La0.7Sr0.3MnO3 (LSMO) thin film
heterostructures grown on MgO and LaAlO3 substrates. Substrate induced strain states generate distinct
magnetic anisotropies, enabling voltage driven tuning between anomalous and topological
Hall contributions. Robust ferroelectric polarization in BTO, confirmed by piezoresponse force microscopy, couples strongly to interfacial orbital reconstruction and carrier redistribution. As a result,
Hall resistivity exhibits
giant low voltage tunability, with up to nearly 93 percent modulation at operating voltages of only 0.5 tand 2 V. Density functional theory calculations further reveal polarization controlled Rashba
spin splitting, establishing a direct link between ferroelectric order and emergent
quantum transport. These findings establish Py/BTO/LSMO
heterostructures as promising candidates for low-power multifunctional spintronic devices, where substrate engineering enables control over emergent
quantum transport phenomena.
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All authors Kusampal Yadav, Kousik Das, Aditya Raj, Mainak Ghosh, Abhishek Kumar, Kartick Biswas, Kalyan Sarkar, Pavan Nukala, Sayantika Bhowal, Devajyoti Mukherjee
Materials Science
Sub-cycle field-driven dynamical Berry phase in solids
Lior Faeyrman, Jianing Zhang, Misha Ivanov et al. (+3 more)
In
quantum mechanics, a wavepacket acquires a
geometric phase, known as the Berry phase, as it evolves along a closed trajectory in parameter space. In condensed matter systems, the Berry phase underlies a broad range of phenomena, including the anomalous
Hall effect, orbital magnetism, and electric polarization. However, in centrosymmetric materials possessing time-reversal (TR)
symmetry, its manifestation is suppressed and effectively vanishes. When a system is driven by a strong terahertz (THz) field, it can be coherently driven far from
equilibrium, transiently reshaping its
symmetry on sub-picosecond timescales. This capability opens new avenues for
quantum control with potential applications in information processing and sensing. Here, we experimentally demonstrate that a strong THz field can transiently break inversion
symmetry in MgO, inducing a dynamical complex Berry phase, thereby manipulating the topological properties of the material. Applying high-harmonic generation (HHG) spectroscopy, we directly resolve the Berry phase, accessing both its real and imaginary components. The first is associated with coherent intraband dynamics while the second with
quantum tunneling through a potential barrier. This observation enables the reconstruction of the time-dependent
evolution of the Berry phase within the cycle of the THz field. The coherent manipulation of solids with strong fields, combined with attosecond-resolved HHG spectroscopy, represents a fundamental step toward unveiling and controlling
geometric quantum phenomena in condensed matter systems.
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All authors Lior Faeyrman, Jianing Zhang, Misha Ivanov, Liang-You Peng, Nirit Dudovich, Riccardo Piccoli
Materials Science
Moiré Strain Skyrmions in Sliding Twisted Bilayers
Rong Hu, Yu-Tao Tan, Dapeng Liu et al. (+2 more)
Strain defect is crucial to the physical properties of solid materials. Among them, strain glass induced by defect engineering provides an important paradigm for nanoscale domain manipulation. Here, we propose purely mechanical moiré strain Skyrmions, a topologically protected elastic textures whose motion can be controlled by interlayer sliding and the chirality of the moiré
bilayer. Using an empirical continuum elastic model combined with
symmetry analysis, we demonstrate the Skyrmion
lattice structure as the elastic ground state. Under interlayer sliding, these moiré strain Skyrmions exhibit the Skyrmion
Hall effect of transverse motion, with a
Hall angle determined by
bilayer chirality and inversely proportional to the moiré twist angle. Our work establishes interlayer sliding as an efficient, low-energy control knob for topological excitations, offering a new paradigm for designing
chiral-material-based information transport devices.
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All authors Rong Hu, Yu-Tao Tan, Dapeng Liu, Yizhou Liu, Jie Ren