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Physics Condensed Matter Materials Science

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Monday 23 March

Materials Science · Cross-listed from cond-mat.supr-con

A possible superconducting gap signature with filling temperature around 40 K in hexagonal iron telluride islands

Guanyang He, Yuxuan Lei, Tianheng Wei et al. (+2 more)

Superconductivity in the iron-chalcogenide series FeSe-Fe(Te, Se)-FeTe has been restricted to the near neighbor of iron selenide (FeSe), with a general consensus that iron telluride (FeTe) is not superconducting. In this study, we report the method to grow FeTe islands with atomically flat surface and hexagonal lattice on SrTiO3 (001) substrates, in which a gap structure with a gap-filling temperature close to 40 K is detected by scanning tunneling spectroscopy. Such signature is examined under various conditions and reminiscent of a superconducting gap structure. This work might offer a potential platform to explore new superconductors at ambient pressure.
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All authors Guanyang He, Yuxuan Lei, Tianheng Wei, Yanzhao Liu, Jian Wang

Materials Science

Magnetocaloric Effect of Pure and Diluted Quantum Magnet Yb$_3$Ga$_5$O$_{12}$

E. Riordan, E. Lhotel, N.-R. Camara et al. (+2 more)

The magnetocaloric effect in the quantum dipolar magnet Yb$_3$Ga$_5$O$_{12}$ is studied both for pure material and with non-magnetic substitution: (Yb$_{1-x}$Y$_x$)$_3$Ga$_5$O$_{12}$. Magnetization measurements have been performed on a single crystal, $x=0$, and on powder samples with $x = 0.2$ and 0.4 in the temperature range between 70 mK to 300 K and in magnetic fields up to 8 T. The magnetic entropy change $\Delta S_m$, a key figure of merit for adiabatic demagnetization refrigeration, has been derived from the magnetization data. The $x=0.2$ sample exhibits the volumetric entropy variation comparable to, and at low fields even enhanced relative to, the pure compound. In contrast, the 40%\ diluted sample shows a reduced effect, consistent with the conventional dilution picture. The Curie-Weiss law fits reveal positive Curie temperatures in both diluted samples, indicating the persistence of ferromagnetic correlations. The robustness of the magnetocaloric response upon moderate dilution highlights the potential of YbGG-based materials for low-temperature magnetic cooling applications, particularly in addressing thermal conductivity challenges through the chemical substitution without compromising cooling power.
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All authors E. Riordan, E. Lhotel, N.-R. Camara, C. Marin, M. E. Zhitomirsky

Materials Science · Cross-listed from physics.chem-ph

Molecular dynamics simulation of high slip flow of water confined between graphene nanochannels at experimentally accessible strain rates

Carmelo Civello, Luca Maffioli, Edward Smith et al. (+4 more)

The transient time correlation function method (TTCF) has emerged as a powerful methodology for accurately probing systems at low shear rates. In the present study, TTCF was used to evaluate the shear rate dependence of the slip length in a high-slip system consisting of water confined between graphene walls at experimentally accessible shear rates, for which classical nonequilibrium molecular dynamics (NEMD) is unfeasible. The corresponding Navier friction coefficient was computed for all shear rates spanning six orders of magnitude and compared with the equilibrium limit. We report for the first time NEMD results obtained at experimentally accessible shear rates using the TTCF approach for a system that has attracted significant interest over the past decades. The slip length calculated with TTCF is in good agreement with previous equilibrium molecular dynamics simulations and experiments. Our aim here is to highlight the extraordinary power of TTCF, particularly for high-slip (low strain-rate) systems, and to verify that equilibrium methods directly match NEMD measurements at experimentally accessible strain rates.
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All authors Carmelo Civello, Luca Maffioli, Edward Smith, James Ewen, Peter Daivis, Daniele Dini, Billy Todd

Materials Science · Cross-listed from physics.chem-ph

olLOSC: Unified and efficient density functional approximation to correct delocalization error in molecules and periodic materials

Yichen Fan, Jacob Z. Williams and Weitao Yang

Density functional theory (DFT) is the most promising method for calculating quantum properties of molecules and materials at moderate and large scales. However, commonly used density functional approximations (DFAs) have systematic delocalization error, as demonstrated by underestimated band gaps, over-delocalized charges, and energy level misalignment at interfaces, which limits its quantitative prediction. Extensive efforts, such as the $GW$ approximation to many-body perturbation theory, system-specific tuning of DFA parameters, and correction functionals have been developed to address delocalization error. However, an accurate, efficient, and unified solution to describe total energy, charge density and band structure for both finite systems and materials is still not available. Building on the linear-response localized orbital scaling correction (lrLOSC), we introduce olLOSC: a localized orbital scaling correction with curvature calculated by orbital-free electronic linear response. olLOSC has comparable accuracy to lrLOSC, but is much more computationally efficient. olLOSC corrects delocalization error - especially underestimated gaps, but also the total energy - both in molecules and in materials with small and moderate band gaps, within the same orbital-free approximation. Critically, with a a unified approximation, olLOSC opens the path for robust and efficient DFT applications across molecules, materials, and interfaces.
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Materials Science

A Unified Heterogeneous Implementation of Numerical Atomic Orbitals-Based Real-Time TDDFT within the ABACUS Package

Taoni Bao, Yuanbo Li, Zichao Deng et al. (+6 more)

We present a unified heterogeneous computing framework for real-time time-dependent density functional theory (RT-TDDFT) based on numerical atomic orbitals (NAOs), implemented in the ABACUS package. We introduce three co-designed abstraction layers, including unified data containers, unified linear algebra operators, and unified grid integration interfaces. These layers collectively accelerate the two most demanding parts of NAO-based RT-TDDFT: explicit real-time wavefunction propagation and real-space grid operations such as Hamiltonian construction and force evaluation under external fields. We validate the method by computing optical properties for systems ranging from finite molecules to periodic solids, showing excellent agreement with standard benchmarks. Performance evaluations on bulk silicon demonstrate that a single GPU can achieve substantial wall-clock speedup over a fully utilized dual-socket CPU node. Furthermore, distributed multi-GPU strong-scaling tests confirm high parallel efficiency over tens of GPUs. This work establishes a high-performance, portable platform for large-scale first-principles simulations of ultrafast electron dynamics.
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All authors Taoni Bao, Yuanbo Li, Zichao Deng, Haotian Zhao, Denghui Lu, Yike Huang, Chao Lian, Lixin He, Mohan Chen

Materials Science

Small-Data Machine Learning Uncovers Decoupled Control Mechanisms of Crystallinity and Surface Morphology in $\beta$-Ga2O3 Epitaxy

Min Peng, Yuanjun Tang, Dianmeng Dong et al. (+12 more)

The ultrawide-bandgap semiconductor $\beta$-Ga2O3 holds exceptional promise for next-generation power electronics and deep-ultraviolet optoelectronics, yet its widespread application is hindered by the lack of cost-effective, high-quality heteroepitaxial thin films. Here, we demonstrate an interpretable machine learning framework that efficiently navigates the complex, multiparameter process space of pulsed laser deposition (PLD) to achieve high-crystallinity $\beta$-Ga2O3 epitaxy on c-plane sapphire. By systematically benchmarking nine regression algorithms under limited experimental data conditions, we identify quadratic polynomial ridge regression as the optimal surrogate model, which combines predictive accuracy (R$^2$ $\approx$ 0.86) with full physical transparency through explicit analytical coefficients. Coupling this model with SHAP (SHapley Additive exPlanations) analysis and iterative experimental design, we construct a closed-loop optimization workflow that progressively refines the process-performance landscape over only three experimental rounds. This data-efficient strategy reduces the X-ray rocking curve (RC) full-width at half-maximum (FWHM) by 70$\%$ from > 3$^{\circ}$ to 0.92$^{\circ}$, which is the best reported value for PLD-grown $\beta$-Ga2O3 on sapphire. Intriguingly, concurrent modeling of surface roughness reveals that crystalline quality and surface morphology are governed by distinct dominant factors: temperature primarily controls bulk crystallinity, whereas oxygen pressure dictates surface kinetics. This decoupled mechanism, quantitatively captured for the first time via feature importance analysis, provides actionable physical insight for independent optimization of structural and morphological properties. Our work establishes a generalizable, resource-efficient paradigm for intelligent process development in oxide epitaxy and beyond.
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All authors Min Peng, Yuanjun Tang, Dianmeng Dong, Yang Zhang, Cheng Wang, Shulin Jiao, Xiaotong Ma, Shichao Zhang, Jingchen Wang, Huiying Wang, Yongxin Zhang, Huiping Zhu, Yue-Wen Fang, Fan Zhang, Zhenping Wu

Materials Science · Cross-listed from cond-mat.stat-mech

Materials Beyond Hamiltonian Limits – Quantum Measurement as a Resource for Material Design

Jochen Mannhart

Recent studies have identified materials and devices whose behavior lies beyond the scope of conventional electronic-structure theory. Such theories are formulated entirely in terms of Hamiltonian evolution and therefore describe only unitary dynamics and thus only a restricted class of quantum systems. In contrast, electron systems that incorporate quantum measurement as an intrinsic dynamical element undergo Hamiltonian evolution interleaved with projection-induced state updates. This unitary-projective dynamics breaks constraints imposed by purely unitary evolution and permits stochastic population transfer between symmetry-related transport channels, thereby enabling fundamentally new material functionalities. This insight motivates the deliberate design of materials and devices that harness unitary-projective dynamics. This article explores the foundations of unitary-projective electron dynamics and charts the resulting landscape of quantum materials and their functionalities. Model calculations demonstrate passive mesoscopic structures with intrinsic nonreciprocal single-electron transmission, materials exhibiting a novel category of magnetism, and possible platforms for energy harvesting and conversion with efficiencies that exceed the standard Carnot limit.
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Materials Science

Electric toroidal octupolar symmetry in pyrite FeS$_2$ probed by Raman optical activity

Yuki Suganuma, Gakuto Kusuno, Hikaru Watanabe et al. (+4 more)

We report Raman optical activity in pyrite FeS$_2$, which hosts an electric toroidal octupolar symmetry. A clear and reproducible sign reversal of the circular intensity difference is observed between neighboring $\{111\}$ faces under cross-circular polarization. The signal appears only for the doubly degenerate $E_g$ phonon mode and is absent for other modes, consistent with symmetry analysis. First-principles calculations reproduce these features, establishing Raman optical activity as a probe of higher-rank axial multipolar symmetry.
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All authors Yuki Suganuma, Gakuto Kusuno, Hikaru Watanabe, Rikuto Oiwa, Hitoshi Mori, Ryotaro Arita, Takuya Satoh

Materials Science · Cross-listed from cond-mat.mes-hall

Antiferromagnetic Pure Spin Current Memdevices

Martin Latorre, Gaspar De la Barrera, Roberto E. Troncoso et al. (+1 more)

Spin currents can be generated through various mechanisms, including the piezospintronic effect, which arises when strain or lattice distortions induce a change in the dipolar spin moment, causing a pure spin current without necessarily being accompanied by net charge transport. This opens new possibilities for low-power information processing and novel device architectures. In this work, we propose a novel effect, the spintronic-magneto-impedictive effect, as the theoretical basis for a pure spin-current memory-like device based on antiferromagnetic components. We focus on materials that can be modeled by the so-called spin-Rice-Mele Hamiltonian, incorporating a magnetic field gradient that explicitly breaks inversion symmetry. Our results shed light on how spin currents are generated and controlled, providing new insights into the potential of these materials for next-generation spintronic technologies.
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All authors Martin Latorre, Gaspar De la Barrera, Roberto E. Troncoso, Alvaro S. Nunez

Materials Science

Exploring self-driving labs for optoelectronic materials

Jonathan Staaf Scragg

Self-driving laboratories (SDLs), by combining automation with machine learning-guided experiment selection, have the potential to transform experimental materials science. To date, most SDLs have been optimisation-driven, designed to rapidly converge on performance metrics, by embedding multiple mechanistic layers within platform-specific surrogate models. Such approaches excel at process tuning yet offer limited insight into the underlying physics governing synthesis-property relationships. Here we articulate a complementary paradigm: the exploration-driven, or scientific, SDL, whose primary purpose is the generation of data for data-driven science. We exemplify this concept for the case of inorganic optoelectronic materials, arguing that defect physics, which forms the central mechanistic link between synthesis conditions and functional properties, provides the foundation for designing a suitable SDL. Because defect populations and their spatial organisation cannot generally be resolved directly - nor fully predicted from first principles - the task of the SDL is to generate datasets in which thermodynamic and kinetic synthesis variables are systematically perturbed and defect-sensitive observables measured in parallel. From this basis, we propose a set of design principles for scientific SDLs that will enable them to operate close to the physics of optoelectronic materials, thereby generating transferrable and reusable datasets offering radical insight. We use Cu2ZnSn(S,Se)4 as a case study, both to show the scale of the task of defect-aware materials exploration as well to highlight as the deficiencies in the current paradigm. We propose that properly designed SDLs can generate the structured datasets necessary to enable mechanistic inference and advance synthesis-aware materials design.
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Materials Science

SAM Molecular Stacking with Heterogeneous Orientationfor High-Performance Perovskite Photovoltaics

Lei Huang, Kai-Li Wang, Zhang Chen et al. (+11 more)

This study demonstrates that thermal-evaporated SAM (eSAM) films, particularly in a thick configuration, spontaneously adopt a heterogeneous molecular orientation, forming a vertical-to-horizontal gradient in molecular packing. This unique architecture establishes a graded energy barrier, which is shown to facilitate more efficient hole transport compared with the single energy barrier presented by conventional thin SAMs. In conclusion, while solution-processed SAMs present formidable scalability challenges, the thermal evaporation of SAMs offers a viable pathway toward industrial-scale fabrication. The strategy of employing thick eSAM films with gradient molecular packing not only circumvents the uniformity issues of solution methods but also introduces a superior structure for charge transport, positioning it as a promising enabler for the commercialization of high-efficiency perovskite photovoltaics. The inability to achieve uniform hole transport with solution-processed self-assembled monolayers (SAMs) constitutes a fundamental bottleneck for scaling perovskite photovoltaics. Herein, we demonstrate that thermal-evaporated SAMs (eSAMs) overcome this limitation by enabling precise thickness control. Crucially, a thickened eSAM spontaneously forms a vertical-to-horizontal gradient in molecular orientation, which creates a descending energy barrier that directionally facilitates hole transport. This tailored interface also ensures excellent surface coverage and directs the growth of high-quality perovskite films. Consequently, the resultant photovoltaic devices set new benchmarks, delivering impressive power conversion efficiencies (PCEs) of 21.46% (small-area, 0.108 cm2) and 19.38% (large-area module, 15.52 cm2) for fully vacuum-evaporated devices, while also setting an impressive PCE of 23.67% for eSAM-based devices with solution-processed perovskites.
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All authors Lei Huang, Kai-Li Wang, Zhang Chen, Zhen-Huang, Saidjafar Murodzoda, Xin Chen, Jing Chen, Chun-Hao Chen, Yu Xia, Yu-Tong Yang, Jia-Cheng Li, Dilshod Nematov, Ilhan Yavuz, Zhao-Kui Wang

Materials Science

Ideal band structures for high-performance thermoelectric materials with band convergence

Yuya Hattori, Hidetomo Usui and Yoshikazu Mizuguchi

We investigate optimal band structures in band-converged systems to achieve high zT using numerical calculations based on a virtual spectral conductivity model. We consider a two parabolic band system, in which multiple band parameters can be independently controlled. Despite its simplicity, this model provides theoretical validation of empirical trends observed in thermoelectric materials. Our results provide a physically transparent set of design principles for band-structure engineering, offering quantitative design guidelines for the development of a wide range of thermoelectric materials. The main conclusions are as follows: (i) When a band does not cross the chemical potential and |{\mu}-E_edge |>5k_B T, the contribution of the band to zT is negligibly small; (ii) To suppress the bipolar effect, a band gap E_g satisfying E_g>5k_B T_op, where T_op is the operating temperature, is required; (iii) In band-converged systems, the energy separation between the band edge {\Delta}E should satisfy {\Delta}E~0 to maximize zT when interband scattering is insignificant; (iv) Achieving high spectral conductivity {\Sigma} (high band degeneracy N, density of states effective mass m_DOS^*, and relaxation time {\tau}) near the band edge is essential for achieving high zT.
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Materials Science

Improved cycling stability and lithium utilization in trilayer Al-LLZO revealed by Electrochemical cycling performance

Naisargi Kanabar, Seiichiro Higashiya and Haralabos Efstathiadis

Garnet-type Li$_{6.25}$Al$_{0.25}$La$_3$Zr$_2$O$_{12}$ (Al-LLZO) solid electrolytes are promising for all-solid-state batteries but are limited by interfacial resistance. In this work, dense and graded tri-layer Al-LLZO electrolytes were fabricated and tested in Li/Al-LLZO/NMC(111) full cells. After 25 cycles, the tri-layer cell delivered discharge capacity of $\sim$55 mAhg$^{-1}$, nearly twice that of the dense Al-LLZO ($\sim$27 mAhg$^{-1}$). EIS showed lower initial interfacial resistance ($\sim$373 $\Omega$) and improved stability. SEM confirmed a porous-dense-porous structure, while NRA revealed enhanced near-surface lithium ($\sim$75%) compared to dense Al-LLZO ($\sim$48%). These results highlight the role of microstructural grading in improving lithium distribution and cell performance.
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Materials Science · Cross-listed from physics.optics

Freeform Spectrally Stable Topological Photonic Vortex Resonators

Yuma Kawaguchi, Daria Smirnova, Filipp Komissarenko et al. (+6 more)

Topological concepts have been at the forefront of materials research in recent years, driving a revolution in our understanding of the response of quantum materials and enabling new ways to manipulate light and sound in topological metamaterials. Topological defects and topological boundaries of different dimensions have driven a paradigm shift in photonics, where topological photonic crystals and metamaterials can be engineered to create one-way flow of energy robust to defects or to control such flows with synthetic degrees of freedom along topological domain walls. More recently, topological point singularities encoded into photonic structures have been shown to enable confinement of optical modes with the topologically nontrivial nature of the cavity imprinted into the vorticity of optical far fields. Here we demonstrate that the two latter concepts - domain wall and point singularities - can be unified into an even more powerful tool to enable arbitrarily shaped resonant cavities of any dimension supporting spectrally stable zero-energy modes. We experimentally confirm that such modes, whose existence is guaranteed by topological principles, allow an unprecedented degree of control over the optical field, which appears to have no phase modulation across space, can have any desirable radiation pattern, and enables spectral stability regardless of shape or length.
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All authors Yuma Kawaguchi, Daria Smirnova, Filipp Komissarenko, Daria Kafeeva, Svetlana Kiriushechkina, Jeffery Allen, Monica Allen, Andrea Alù, Alexander Khanikaev

Materials Science · Cross-listed from cond-mat.str-el

Control of band structure in the altermagnetic candidate MnTe by temperature and strain

Shin-ichi Kimura, Hironao Suwa, Kangle Yuan et al. (+4 more)

The temperature and strain dependences of the optical conductivity spectrum of hexagonal manganese telluride (MnTe) were measured, revealing absorption in the terahertz (THz) region from spin-split bands to acceptor levels. The temperature dependence of the THz absorption peak is consistent with that of a ferromagnetic phase transition, even though MnTe exhibits no net magnetism. The temperature dependence was attributed to a change in the altermagnetic electronic structure. Under negative uniaxial strain, the THz peak shifts to the high-energy side, suggesting spin-splitting bands at energies away from EF, consistent with the theoretical prediction that the spin-splitting angle decreases. The observed behavior of the THz peak clearly shows that MnTe has the altermagnetic electronic structure. Additionally, a Fano-like asymmetric line shape in the optical phonon absorption was observed, possibly originating from interactions with the alternative spin-split bands.
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All authors Shin-ichi Kimura, Hironao Suwa, Kangle Yuan, Hiroshi Watanabe, Takuto Nakamura, Haan Kyul Yun, Myung-Hwa Jung

Sunday 22 March

Materials Science

Inverse design of heterodeformations for strain soliton networks in bilayer 2D materials

Md Tusher Ahmed and Nikhil Chandra Admal

Strain soliton networks strongly influence the structural and electronic properties of heterodeformed bilayer systems, yet their design remains challenging due to the high dimensionality of heterodeformation space and the absence of a direct map between deformation and network geometry. In this work, we introduce a geometric framework that establishes a one-to-one mapping between heterodeformations and the geometry of the strain soliton network expressed as line vector-Burgers vector pairs. The admissible networks are constrained by topology dictated by the generalized stacking fault energy landscape. We show that the moiré Bravais lattice, corresponding to a uniform heterodeformation, alone is insufficient to characterize the interface: distinct heterodeformations can share identical moiré Bravais lattices while producing different soliton networks, reflecting an inherent many-to-one mapping when only translational symmetry is considered. In contrast, the soliton network encodes the full multilattice geometry of the interface, including topology and connectivity, which are not captured by the moiré Bravais lattice alone. The proposed framework enables the direct construction of heterodeformations from target networks, providing a systematic route for inverse design of moiré interfaces beyond conventional twist-based approaches.
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Materials Science · Cross-listed from quant-ph

Enhanced Emission from Boron-Vacancy Center in Rhombohedral Boron Nitride

Nasrin Estaji, Ismaeil Abdolhosseini Sarsari, Gergő Thiering et al. (+1 more)

Boron nitride is a layered crystal whose properties depend on how its atomic sheets are stacked. Its negatively charged boron vacancy is a well-established magnetic defect that can be prepared and read out optically, but in the common hexagonal form it emits very little light, because the symmetry of the surrounding lattice forbids the relevant optical transition. Here we show, using first-principles calculations, that stacking the sheets in the rhombohedral sequence instead removes this restriction and increases the emitted intensity by one to two orders of magnitude, while the magnetic properties remain comparable or improve. We predict that the resulting emission is bright enough for a single defect to be addressed at room temperature, and that a sharp emission line, absent in the hexagonal form, should appear on cooling. Stacking order therefore acts as a design parameter for tailoring the quantum properties of defects embedded in layered materials.
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All authors Nasrin Estaji, Ismaeil Abdolhosseini Sarsari, Gergő Thiering, Adam Gali

Materials Science

Engineering magnetism in hybrid organic-inorganic metal halide perovskites

Yaiza Asensio, Lucía Olano-Vegas, Samuele Mattioni et al. (+4 more)

The chemical and structural flexibility of hybrid organic-inorganic metal halide perovskites (HOIPs) provides an ideal platform for engineering not only their well-studied optical properties, but also their magnetic ones. In this review we present HOIPs from a new perspective, turning the attention to their magnetic properties and their potential as new class of on-demand low-dimensional magnetic materials. Focusing on HOIPs containing transition metals, we comprehensively present the progress that has been made in preparing, understanding and exploring magnetic HOIPs. First, we briefly introduce HOIPs in terms of composition and crystal structure and examine the synthesis protocols commonly used to prepare those showing magnetic properties. Then, we present their rich magnetic behavior and phenomenology; discuss their origin and guidelines for tuning them by changing the perovskite phase, chemical composition and dimensionality; and showcase their potential application in magneto-optoelectronics and spintronics. Finally, we describe the current challenges in the field, such as their integration into devices, as well as the emerging possibilities of moving from magnetic doping to pure transition metal-based HOIPs, which will motivate further studies in the future.
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All authors Yaiza Asensio, Lucía Olano-Vegas, Samuele Mattioni, Marco Gobbi, Fèlix Casanova, Luis E. Hueso, Beatriz Martín-García

Materials Science

Disentangling Anomalous Hall Effect Mechanisms and Extra Symmetry Protection in Altermagnetic Systems

Yuansheng Bu, Ziyin Song, Zhong Fang et al. (+2 more)

We investigate the evolution of Anomalous Hall Conductivity (AHC) in a coplanar and collinear antiferromagnetic system with varying spin canting angles. A tight-binding model based on three t2g-orbitals in a body-centered tetragonal lattice is constructed, where the inclusion of third-nearest neighbor hopping is demonstrated to be essential for capturing the characteristic energy band splitting of altermagnetic materials. By employing a symmetry analysis based on spin space groups and treating spin-orbit coupling (SOC) as a perturbation, we theoretically distinguish and numerically verify two origins of the transverse transport: the conventional anomalous Hall effect (AHE) induced by net magnetization and the Crystal Hall Effect (CHE) arising from specific crystal symmetries. Our results show that the conductivity components driven by these two mechanisms follow distinct trigonometric dependencies on the canting angle. Crucially, we identify a hidden C110 rotational symmetry that has been previously overlooked in static magnetic group analyses. By expanding the AHC in terms of spin orientation vectors, we demonstrate that this symmetry acts as a bridge connecting distinct magnetic configurations with different canting angles, thereby strictly protecting the equivalence of orthogonal conductivity components in the collinear system.
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All authors Yuansheng Bu, Ziyin Song, Zhong Fang, Quansheng Wu, Hongming Weng

Materials Science

Towards Computational Microscope of Chemical Order-Disorder via ML-Accelerated Monte Carlo Simulation

Fanli Zhou, Hao Chen, Pengxiang Xu et al. (+3 more)

Tailoring the performance of next-generation high entropy materials requires a deep understanding of the competition between entropy-driven random solid solution and enthalpy-driven chemical ordering. Investigating such order and disorder complexity demands atomistic simulations that achieve high accuracy, efficiency, and generalizability across vast spatial, temporal, and especially chemical scales. While machine learning (ML) interatomic potentials have transformed molecular dynamics, they remain limited in capturing diffusion-driven chemical evolution over long timescales. The recently introduced SMC-X method brings exciting opportunities. Realizing its full potential requires a comprehensive study, which is the focus of this work. To assess model performance, we systematically benchmark invariant and equivariant architectures using a density functional theory dataset of more than 10,000 configurations spanning seven elements: Fe, Co, Ni, Al, Ti, Ta, and V. To understand the roles of pairwise and higher-order interactions, we decouple their contributions across chemical space using an explainable machine learning approach. We also examine the impact of lattice relaxation by comparing models trained on datasets with and without structural relaxation. Our results clarify how to choose ML surrogate models for Monte Carlo simulations, bridge the gap between theory and experiment, and lay a foundation for establishing ML-accelerated Monte Carlo as a computational microscope for chemical complexity.
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All authors Fanli Zhou, Hao Chen, Pengxiang Xu, Kai Yang, Zongrui Pei, Xianglin Liu

Materials Science · Cross-listed from cond-mat.str-el

Orbital-specific Itinerancy and Localization in a Kagome Magnet

S.V. Streltsov, H.Y. Huang, A. Ushakov et al. (+10 more)

The kagome lattice naturally hosts flat bands, Dirac fermions, and van Hove singularities, yet whether its geometry can stabilize orbital-selective phases - a hallmark of Hund's physics in multi-orbital correlated systems - has remained an open question. Here, we combine resonant inelastic X-ray scattering with density functional theory and dynamical mean-field theory to demonstrate that YMn$_6$Sn$_6$ exhibits a spontaneous orbital differentiation into coexisting itinerant and localized electrons within the same Mn $3d$ manifold. Orbitals directed along Mn-Mn bonds provide coherent quasiparticles and metallic bands, while those pointing toward ligands become strongly correlated and display non-Fermi-liquid behavior. Hund's intra-atomic exchange suppresses orbital fluctuations, stabilizing this dichotomy and providing a natural double-exchange-like mechanism for the observed ferromagnetic bilayer coupling. Our work establishes YMn$_6$Sn$_6$ as a kagome platform where orbital selectivity, flat-band topology, and Hund's metallicity converge - revealing that geometric frustration and correlation-driven orbital differentiation can cooperatively design exotic quantum phases beyond the canonical paradigms of Mott physics or band topology alone.
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All authors S.V. Streltsov, H.Y. Huang, A. Ushakov, C.I. Wu, A. Singh, J. Su, J. Okamoto, C.T. Chen, K. Wang, A.I. Poteryaev, S-W. Cheong, A. Fujimori, D. J. Huang

Materials Science

First Plasma Atomic Layer Etching of Diamond via O$_2$/Kr Chemistry

Duc Duy Tran, Cedric Mannequin, Aboulaye Traore et al. (+2 more)

We report the first plasma atomic layer etching (ALE) process for diamond using a cyclic plasma sequence composed of two separated steps: oxygen surface modification and krypton ion removal. The process is implemented in an inductively coupled plasma reactor using alternating O$_2$ plasma exposure and low-energy Kr ion bombardment. This cyclic process exhibits the characteristic self-limiting behavior of ALE and enables controlled material removal with atomic-scale precision. An etch depth per cycle of \SI{6.85}{\angstrom} was achieved. Surface analysis reveals that the etched diamond surfaces exhibit lower roughness than the pristine material, while XPS confirms the preservation of the diamond bonding structure and indicates essentially damage-free etching. These results demonstrate that plasma ALE based on O$_2$/Kr chemistry provides a viable route toward damage-controlled nanoscale processing of diamond, opening new opportunities for advanced device fabrication in power electronics, photonics, quantum sensing and quantum computing technologies.
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All authors Duc Duy Tran, Cedric Mannequin, Aboulaye Traore, Masahiro Sasaki, Etienne Gheeraert

Materials Science

Framework for Quasiperiodic Interfaces: Proximal Coincidence Point Set and Computation

Suining Xiong, Wenwen Zou, Pingwen Zhang et al. (+1 more)

We present a unified theoretical and computational framework that bridges mathematical quasiperiodicity with classical crystallographic models. Based on a rigorous cut-and-projection construction, the proposed proximal coincidence point set (PCPS) theory extends the classical coincidence site lattice model and further incorporates physically motivated perturbations encoding interfacial atomic mobility as well as visual indistinguishability. Spectral characteristics of PCPS naturally motivate a conserved Landau-Brazovskii model combined with projection method, yielding unified high accuracy in resolving quasiperiodic order across the entire interfacial plane. Representative quasiperiodic features are revealed in our numerical results, including generalized Fibonacci sequences in BCC [110] tilt GBs, as well as repetitive patterns within the interstices of dislocation networks in low-angle BCC [100] twist GBs and phase boundaries between BCC and face-centered cubic crystals. In high-angle BCC [100] twist GBs, 12- and 8-fold quasicrystals emerge, while the PCPS theory combined with cyclotomic field projections further explains their restrictions of non-crystallographic symmetries. This framework not only provides a rigorous theoretical explanation for interface structures but also offers a path toward modeling other types of incommensurate structures.
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All authors Suining Xiong, Wenwen Zou, Pingwen Zhang, Kai Jiang

Materials Science

Unlocking Static Polarization and Strain Density Waves in Perovskites by Softening a Hidden Antiferrodistortive Tilt Gradient Mode

Yajun Zhang, Devesh R. Kripalani, Xu He et al. (+9 more)

Spin density waves (SDWs) represent a fundamental paradigm of spatially modulated order in condensed matter systems, yet their electrical and mechanical analogues polarization and strain density waves (PDWs and StDWs) have remained elusive as equilibrium phases. Here, we introduce a general, symmetry-driven strategy to unlock static PDWs and StDWs in perovskites SrTiO3 and SrMnO3. Using first-principles calculations, we uncover a previously overlooked soft antiferrodistortive tilt gradient mode at small-q wavevector in the phonon dispersion of their presumed Ima2 ground state under moderate tensile strain. Group-theory analysis reveals that a hard polaracoustic phonon, which intrinsically carries PDWs and StDWs, is improperly destabilized by a trilinear coupling with this modulated tilt mode and an inherently uniform tilt mode. This interaction drives a structural transition from the Ima2 phase to a novel lower-energy Pmn21 phase that hosts long-range-ordered PDWs and StDWs. Strikingly, the engineered StDWs in SrMnO3 activate an electrically tunable SDW via the flexomagnetic effect. These discoveries fundamentally revise the strain-phase diagrams of prototypical perovskites and establish a unified phonon-engineering framework that links modulated phonon instabilities to targeted density-wave order, offering new pathways for designing advanced electromechanical and magnetoelectric functionalities.
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All authors Yajun Zhang, Devesh R. Kripalani, Xu He, Konstantin Shapovalov, Jiyuan Yang, Hongjian Zhao, Shi Liu, Huadong Yong, Xingyi Zhang, Jie Wang, Kun Zhou, Philippe Ghosez

Materials Science · Cross-listed from cond-mat.soft

Isometric Incompatibility in Growing Elastic Sheets

Yafei Zhang, Michael Moshe and Eran Sharon

Geometric incompatibility, the inability of a material's rest state to be realized in Euclidean space, underlies shape formation in natural and synthetic thin sheets. Classical Gauss and Mainardi-Codazzi-Peterson (MCP) incompatibilities explain many patterns in nature, but they do not exhaust the mechanisms that frustrate thin elastic sheets. We identify a new incompatibility that forbids smooth stretching-free configurations, even when the rest state of the elastic sheet locally satisfies the Gauss and MCP compatibility conditions. We demonstrate this principle in a model of surface growth with positive Gaussian curvature, where a geometric horizon forms, leading to the onset of frustration. Experiments, simulations, and theory show that the sheet responds by nucleating periodic d-cone-like dimples. We show that this obstruction to stretching-free configurations is topological, and we point to open questions concerning the origin of frustration.
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Materials Science

High Entropy Alloy under Shock Compression: Optical-Pump X-Ray-Probe

Hsin Hui Huang, Meguya Ryu, Shuji Kamegaki et al. (+23 more)

High entropy alloys (HEAs) are multi-principal-element alloys designed for tailorable mechanical performance and have been attracting significant engineering interest, yet their fundamental behaviour under extreme dynamic conditions, such as shock loading, remains unexplored. Here, we report laser-shock experiments on two different types of 1-micrometers-thick HEA microfilms, CuPdAgPtAu and CrFeCoNiCuMo, on 25-micrometers-thick black-Kapton ablator driven by a high intensity laser pulse (532 nm, 5 ns, 16 J, 0.5-mm diameter focal spot) and probed by an X-ray free electron laser (XFEL) pulse (12 keV, 7 fs). Time-resolved X-ray diffraction (XRD) shows the formation of a transient phase with a lattice compression up to 5.1% of the CuPdAgPtAu HEA along the (111) plane; this transient compressed phase existed for 0.3 ns. The impedance matching Hugoniot analysis estimated a shock pressure of 55 +/- 6 GPa in the HEA film, while Au- and Fe-based equations of state (EoS) modelling predict 80 GPa (0.8 MBar) at the free HEA surface. The free HEA surface reached maximum velocities of ~ 5 km/s as recorded from in situ monitoring with the velocity interferometry system for any reflector (VISAR) imaging. These initial HEA results show the suitability of HEA sample preparation and XFEL-based XRD characterisation under extreme shock loading, and are promising for experimental determination of the EoS of this emerging class of materials (beamtime proposal No.: 2024A8503 for a 6-hour preliminary experiment).
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All authors Hsin Hui Huang, Meguya Ryu, Shuji Kamegaki, Dominyka Stonyte, Tadas Malinauskas, Yoshiaki Nishijima, Rosalie Hocking, Nguyen Hoai An Le, Tomas Katkus, Haoran Mu, Soon Hock Ng, Samuel Pinches, Andrew S.M. Ang, Vygantas Mizeikis, Nadia Zatsepin, Kohei Miyanishi, Toshinori Yabuuchi, Hirotaka Nakamura, Alexis Amouretti, Norimasa Ozaki, Tommaso Vinci, Arturas Vailionis, Eugene G. Gamaly, Damien G. Hicks, Junko Morikawa, Saulius Juodkazis

Saturday 21 March

Materials Science · Cross-listed from physics.optics

Understanding inhomogeneous crystallization dynamics of phase-change materials in the vicinity of metallic nanoantennas

Luis Schüler, Lukas Conrads, Yingfan Chen et al. (+5 more)

Optical metasurfaces composed of metallic or dielectric scatterers (meta-atoms) promise a powerful way of tailoring light-matter interactions. Phase-change materials (PCMs) are prime candidates for non-volatile resonance tuning of metasurfaces based on a refractive index change. Precise resonance control can be achieved by locally applying laser pulses to crystallize a PCM, modifying the dielectric surrounding of meta-atoms. However, the complex crystallization kinetics of PCMs in the vicinity of metallic meta-atoms have not been studied yet. Here, we experimentally investigate metallic dimer antennas on top of the PCM Ge3Sb2Te6 and address these nanoantennas with laser pulses. Our study reveals inhomogeneous crystallization caused by the absorption and heat conduction of the metallic nanoantennas. A self-consistent multiphysics model, including electromagnetic, thermal, and phase-transition processes, is employed to simulate the crystallization and understand the resulting resonance shift of the antennas. This model enables the optimization of the laser parameters and the geometry of the meta-atoms to achieve an optimal crystallization pattern and resonance shift. Our work paves the way towards complex antenna geometries optimized for local addressing of PCMs to achieve sophisticated crystallization patterns, enabling on-demand programming of individual nanoantennas within metasurfaces.
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All authors Luis Schüler, Lukas Conrads, Yingfan Chen, Lina Jäckering, Sebastian Meyer, Matthias Wuttig, Thomas Taubner, Dmitry N. Chigrin

Materials Science · Cross-listed from cond-mat.mes-hall

Chern Insulator in magnetic-doped two-dimensional semiconductors

Dinh Loc Duong

We propose an approach to induce nontrivial bands with non-zero Chern numbers by utilizing strong spin-orbit coupling in transition metal dichalcogenides with dopants. We demonstrate that a doped state near the valence-band edge induces band inversion with the hybridized host band, leading to topologically non-trivial properties. Calculations for V-doped WSe2 and WS2 confirm this mechanism. The coexistence of magnetic order and nontrivial topology in these systems offers a promising platform for exploring the quantum anomalous Hall effect.
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Materials Science

From Photons to Electrons: Accelerated Materials Discovery via Random Libraries and Automated Scanning Transmission Electron Microscopy

Boris Slautin, Kamyar Barakati, Utkarsh Pratiush et al. (+10 more)

The real-world implementation of materials prediction algorithms remains limited by persistent characterization bottlenecks in materials discovery, where photon-based probe techniques (e.g., XRD or Raman) impose long acquisition times and access latencies, restricting exploration to quasi-ternary composition spaces typically realized as compositional libraries. Here, we argue that a paradigm shift from photon- to electron-based characterization can realign materials characterization with modern high-throughput synthesis. We formulate cost functions and exploration strategies for STEM-based chemical and structural characterization and use Monte Carlo simulations to show that random chemical libraries, where compositionally distinct regions are co-located within a single specimen and interrogated in situ by electron spectroscopies, can sample high-dimensional composition and phase spaces with orders-of-magnitude greater effective coverage than conventional spread-library/X-ray approaches. We further demonstrate autonomous discovery on a laboratory STEM platform, where ML-based autotuning and scripted control enable iterative region selection and characterization without human intervention. Finally, we outline extensions to labeled or position-encoded libraries that preserve compositional and processing metadata, enabling joint exploration of composition and process spaces. Together, these results establish electron-based, ML-enabled STEM as a scalable pathway toward combinatorially rich materials discovery.
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All authors Boris Slautin, Kamyar Barakati, Utkarsh Pratiush, Christopher D. Lowe, Catherine C. Bodinger, Brandi M. Cossairt, Mahshid Ahmadi, Austin Houston, Timur Bazhirov, Jaehyung Lee, Kamal Choudhary, Gerd Duscher, Sergei Kalinin

Materials Science · Cross-listed from cond-mat.mes-hall

Breakdown of Topological Inheritance and Twist-Induced Quantum Geometry Reconfiguration in Moiré Flat Bands

Yi-Chun Hung, Xiaoting Zhou and Arun Bansil

Since the inception of moiré quantum matter, a foundational tenet of the field has been that the quantum geometry of emergent flat bands is faithfully inherited from the low-energy valleys of the constituent monolayers. Here, we demonstrate a breakdown of this longstanding tenet in twisted bilayers of loop-current-ordered kagome lattices (tb-LCK). Using microscopic tight-binding modeling, we reveal a twist-induced reconfiguration of quantum geometry where realistic interlayer hybridization quenches topological inheritance from the monolayer. By tuning the loop-current phase, we identify distinct regimes in which the monolayer Berry curvature is either substantially redistributed or entirely suppressed in the moiré flat bands. We further show that this quantum geometric collapse is expected to be readily accessible in vanadium-based kagome metals such as AV$_{\text{3}}$Sb$_{\text{5}}$, and that Floquet engineering via waveguide laser illumination offers a practical route to turn topological inheritance on and off. Our findings uncover a universal mechanism for quantum geometric reconstruction, establishing interlayer coupling strength as an independent parameter for tuning band topology beyond the weakly coupled van der Waals heterostructure paradigm.
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