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Physics Condensed Matter Materials Science

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Friday 8 May

Materials Science

Anisotropic Defect Diffusion in Layered CsPbBr$_\mathrm{x}$I$_\mathrm{3-x}$ Perovskites

Konrad Wilke, Mike Pols, Titus S. van Erp et al. (+2 more)

Mixed-halide perovskites offer a route to enhance phase stability and modify optoelectronic properties. Here, we use large-scale molecular dynamics simulations with a reactive force field to investigate defects in CsPbBr$_\mathrm{x}$I$_\mathrm{3-x}$ perovskites, focusing on how defect mobility can be controlled and the stability of the material improved by layered ordering of Br and I anions. Our results show that layered halide ordering induces strongly anisotropic defect diffusion: migration proceeds readily along the layers, whereas diffusion across them is strongly suppressed. For Cs defects, this anisotropy originates from directional lattice strain and the associated octahedral tilting, whereas halide migration is governed by an interplay between strain and preferential local halide bonding configurations.
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All authors Konrad Wilke, Mike Pols, Titus S. van Erp, Geert Brocks, Shuxia Tao

Materials Science · Cross-listed from physics.optics

Hot biexcitons driven by extreme optical confinement

Xinyi Wang, Kaushik Kudtarkar, Wenjing Wu et al. (+6 more)

A powerful means to understanding condensed matter that possesses a multi-constituent, non-isolated, and complex nature, with a preeminent example being two-dimensional (2D) materials, is studying many-body interactions. However, experimentally observing high-order many-body interactions is a daunting task due to its heavy reliance on the abundance of low-order complexes. Here, we report the observation of four-body hot biexcitons in an energetically unfavorable bilayer of tungsten disulfide (WS2) through creating extreme optical confinement. Specifically, we integrate a non-radiative bound state in the continuum (BIC) into a photonic crystal (PhC) defect cavity, forming a quasi-three-dimensional (q-3D) but open confinement for photons at the driving frequency. The extremely confined photons in both reciprocal and physical spaces then excite inherently unproductive two-body hot excitons situated slightly above the indirect bandgap so efficiently that they form overwhelmed higher-order four-body hot biexcitons. Distinctively, these hot biexcitons exhibit substantial valley polarization and coherence at room temperature, which we attribute to the topological nature of BICs and the associated q-3D confinement with an orbital angular momentum. Besides achieving room-temperature biexcitons, the q-3D confinement could be valuable for higher-order interactions, such as triexcitons, and many other many-body phenomena, including Bose-Einstein condensation.
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All authors Xinyi Wang, Kaushik Kudtarkar, Wenjing Wu, Yunjo Jeong, Yuxuan Cosmi Lin, Xiaofeng Qian, Junichiro Kono, Shengxi Huang, Shoufeng Lan

Materials Science

MatterSim-MT: A multi-task foundation model for in silico materials characterization

Han Yang, Xixian Liu, Chenxi Hu et al. (+25 more)

Accurate property characterization is a major bottleneck in materials design. While first-principles methods and task-specific machine-learning models have driven important progress, they remain fundamentally limited in scalability and generalizability across the vast space of structures and properties relevant to real-world materials design. We present MatterSim-MT, a multi-task foundation model for in silico materials simulation and property characterization. The model is pretrained on over 35 million first-principles-labeled structures covering 89 elements, temperatures up to 5000 K and pressures up to 1000 GPa, and is fine-tuned on various properties including Bader charges, magnetic moments, Born effective charges, and dielectric matrices. Out of the box, MatterSim-MT not only serves as a foundation model for predicting material structure, dynamics and thermodynamics, its multi-task architecture also enables a wide range of complex simulations that cannot be captured by potential energy surfaces alone. For example, we demonstrate pressure-dependent LO-TO phonon splitting in SiC with close agreement with experiment, electric hysteresis in ferroelectric BaTiO3, and the cationic-to-anionic redox transition during delithiation of a Li-rich cathode material. Finally, we show that MatterSim-MT scales well with more data and parameters, can be efficiently fine-tuned to higher levels of theory, and can be efficiently extended to new systems via active learning. Overall, we believe this approach provides a scalable route to accurate in silico materials characterization.
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All authors Han Yang, Xixian Liu, Chenxi Hu, Yichi Zhou, Yu Shi, Chang Liu, Junfu Tan, Jielan Li, Guanzhi Li, Qian Wang, Yu Zhu, Zekun Chen, Shuizhou Chen, Fabian Thiemann, Claudio Zeni, Matthew Horton, Robert Pinsler, Andrew Fowler, Daniel Zügner, Tian Xie, Lixin Sun, Yicheng Chen, Lingyu Kong, Yeqi Bai, Deniz Gunceler, Frank Noé, Hongxia Hao, Ziheng Lu

Materials Science

Interfacial control of hot-carrier extraction and photostability in two-dimensional materials

Claudia Gollner, Mohammad Taghinejad, Chenyi Xia et al. (+8 more)

Two-dimensional transition metal dichalcogenides (TMDCs) are promising materials for next-generation optoelectronic devices, yet their implementation is hindered by limited sample stability and challenges in forming reliable electrical contacts. Here, by utilizing time-domain THz emission spectroscopy we directly probe charge carrier dynamics in monolayer WS2 on gold (Au) and fused silica (SiO2) as a function of interface morphology. For laser excitation above the band gap of WS2, we independently extract effective transport times for both electrons and holes and find that discontinuous WS2 contacts on rough Au generate larger net photocurrents than uniform, strongly coupled interfaces - a counterintuitive observation attributed to imbalanced electron and hole transfer from WS2 to Au. Crucially, we demonstrate that ultrafast charge extraction and separation suppress recombination-driven energy release and thereby prevent photo-induced degradation under ambient conditions, eliminating the need for encapsulation. These findings redefine interfacial design as a central control parameter for both performance and stability in 2D optoelectronic devices.
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All authors Claudia Gollner, Mohammad Taghinejad, Chenyi Xia, Zhepeng Zhang, Fang Liu, Francesco Laudani, Annette Foelske, Mark L. Brongersma, Andrew J. Mannix, Tony F. Heinz, Aaron Lindenberg

Materials Science

Anomalous magnetotransport in a non-collinear correlated kagome ferromagnet MgMn6Sn6

Kakan Deb, Sourav Kanthal, Jyotirmoy Sau et al. (+5 more)

Magnetic kagome metals provide a fertile platform for exploring unusual magnetotransport phenomena arising from the intricate interplay between electronic topology, electron correlations, and magnetic order. MgMn6Sn6 is a room-temperature kagome ferromagnet with strong in-plane magnetic anisotropy. Here, we report a combined study of single-crystal neutron diffraction (SCND) and magnetotransport properties of MgMn6Sn6, supported by first-principles calculations. Our SCND measurements reveal a non-collinear arrangement of Mn magnetic moments within the basal plane of the kagome bilayer. The Hall conductivity shows a substantial intrinsic contribution of approximately 0.29 e^2/h per kagome layer, which is nearly isotropic with respect to the field orientation. At low temperatures, the anomalous Hall conductivity develops a pronounced anisotropic extrinsic component, highlighting the directional sensitivity of scattering processes. The significantly large value of the Sommerfeld coefficient, in the absence of f-electrons, underscores enhanced electron correlation. Therefore, the non-collinear kagome ferromagnet MgMn6Sn6 is a promising candidate for studying the effects of electron correlation on magnetotransport properties.
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All authors Kakan Deb, Sourav Kanthal, Jyotirmoy Sau, Chandra Shekhar, Manoranjan Kumar, Matthias Gutmann, Jhuma Sannigrahi, Nitesh Kumar

Materials Science

Ferroelectric domains in methylammonium lead iodide perovskite thin-films

Holger Röhm, Tobias Leonhard, Michael J. Hoffmann et al. (+1 more)

We explore the ferroic properties of methylammonium lead iodide perovskite solar cells by Piezoresponse Force Microscopy (PFM). In vertical and horizontal PFM imaging, we find domains of alternating polarization with a width of 90 nm which we identify as polarized ferroelectric domains. High-resolution photo-conductive atomic force micrographs under illumination also show alternating charge carrier extraction patterns which we attribute to the local vertical polarization components within the ferroelectric domains. The correlation of the sample properties with Atomic Force and Kelvin Probe Force Micrographs evidence the piezo-electric nature of the domains.
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All authors Holger Röhm, Tobias Leonhard, Michael J. Hoffmann, Alexander Colsmann

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

Beyond the conventional Emery model: crucial role of long-range hopping for cuprate superconductivity

Eric Jacob, M. O. Malcolms, Viktor Christiansson et al. (+6 more)

The Emery model is the quintessential model for cuprate superconductors. In his eponymous paper, Emery only considered the next-nearest-neighbor oxygen-copper hopping. Later, also the relevance of nearest- and next-nearest oxygen-oxygen hoppings has been pointed out. Using dynamical vertex approximation, we find a superconducting dome consistent with cuprates. However, long-range hoppings beyond the three conventional hopping parameters are necessary for the quantitatively correct phase diagram and for a proper d-wave order parameter.
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All authors Eric Jacob, M. O. Malcolms, Viktor Christiansson, Leonard M. Verhoff, Paul Worm, Liang Si, Philipp Hansmann, Thomas Schäfer, Karsten Held

Materials Science

Selectivity- and Activity-Aware Catalyst Descriptors for CO$_2$ Hydrogenation on Alloy Nanocatalysts using Machine-Learned Force Fields

Prajwal Pisal, Ondřej Krejčí and Patrick Rinke

Adsorption energy distributions (AEDs) have emerged as a powerful and increasingly adopted descriptor for catalytic performance in high-entropy alloys and, more recently, in conventional metallic alloy nanocrystal catalysts. By accounting for diverse adsorption sites and crystallographic facets, AEDs more fully represent nanoparticle-based catalytic surfaces and show strong promise for accelerating rational design and discovery of heterogeneous catalysts, especially for CO$_2$ hydrogenation. However, previous high-throughput screenings have not provided simultaneous facet-level insight into catalytic activity, product selectivity, and thermodynamic stability. Here, we implement and extend the AED framework to individual crystallographic facets, combining facet-resolved adsorption fingerprints with Wulff-derived facet abundances and an interpretable latent-space analysis of C1-product selectivity. We employ universal machine-learned force fields trained on Open Catalyst Project data to compute adsorption energies across 226 experimentally observed metals, binary alloys, and previously unexplored ternary alloys, encompassing ~1.4 million adsorption configurations on >2,600 crystallographically distinct surfaces. Using distribution-based similarity analysis and principal component analysis of AED moments, we identify composition-facet combinations with adsorption landscapes associated with activity and qualitative selectivity trends toward methanol, methane, formic acid, and CO. Our framework links surface structure to adsorption-based catalytic trends, providing experimentally testable composition-facet candidates for further investigation and validation.
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Materials Science · Cross-listed from physics.optics

Active Control of Topological Exceptional Points in Non-Hermitian Metasurfaces

Parul Sharma, Sobhan Subhra Mishra, Yash Gupta et al. (+4 more)

Active control and ultrafast switching of non-Hermitian photonic systems are essential for next-generation reconfigurable optical technologies. Here, we demonstrate dynamic temporal manipulation of EPs in the terahertz (THz) regime using optically excited germanium (Ge) as an active medium. By exploiting pump-probe delay as a continuous tuning parameter, we achieve sub-picosecond eigenmode switching (~0.5 ps) and realize a complete time-resolved EP encirclement within ~2 ps, enabling direct observation of topological phase accumulation. At EP, the metasurface exhibits highly asymmetric transmission for circularly polarized light, characteristic of chiral mode response. Furthermore, we observe ultrafast eigenmode switching and topological phase evolution within ~1 ps, achieving >99% cross-polarization modulation depth. The measured results show strong agreement with theoretical modeling, with a high Petermann factor of approximately 10^3, confirming the effectiveness of the design. Our work establishes pump-probe delay time as a dynamical control parameter for EP topology, introducing a new regime of ultrafast non-Hermitian photonics for high-speed switching, enhanced sensitivity, and tunable polarization control in the THz domain.
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All authors Parul Sharma, Sobhan Subhra Mishra, Yash Gupta, Brijesh Kumar, Ranjan Singh, Abhishek Kumar, Anshuman Kumar

Materials Science

Epitaxial growth of beta-bismuthene on Sb2Te3

Giorgia Sementilli, Arslan Masood, Fabio Ronci et al. (+7 more)

Over the past decades, two-dimensional crystals have attracted considerable interest as promising materials for electronic and optoelectronic applications. Among them, graphene analogs composed of heavy atoms occupy a particularly distinctive niche due to their enhanced spin-orbit interaction. Here, we present an epitaxial heterointerface formed by beta-bismuthene on Sb2Te3, a well-known three-dimensional topological insulator. Using scanning tunneling microscopy, we systematically investigated the effects of Bi coverage and substrate temperature on nucleation processes, island morphology, and atomic structure. In addition, substrate-induced defects were identified throughout the bismuthene lattice.
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All authors Giorgia Sementilli, Arslan Masood, Fabio Ronci, Stefano Colonna, Marilena Carbone, Marco Papagno, Ziya S. Aliev, Evgueni V. Chulkov, Sergey V. Eremeev, and Roberto Flammini

Materials Science

Harnessing Structural Disorder: Unraveling Hydrogen Evolution in Monolayer Amorphous Carbon via First-Principles Simulations and Machine-Learned Potentials

Sreehari M S, Ashutosh Krishna Amaram and Raghavan Ranganathan

Disorder and defective coordination in the catalytic plane are crucial for enhancing the Hydrogen Evolution Reaction (HER) on two-dimensional catalysts. Amorphous materials are disordered, making them catalytically adaptive for many reactions. In this work, the HER capabilities of Monolayer Amorphous Carbon (MAC) were studied in comparison with crystalline carbon derivatives, such as pristine graphene (GE) and graphyne derivatives. MAC generated from melt-quench simulations revealed a diverse framework of predominantly sp2 and sp3 carbons with numerous 5-, 6-, and 7-membered rings. Density Functional Theory (DFT) calculations investigated free-energy variations in hydrogen adsorption for each material. According to Sabatier's principle, optimum activity is achieved when the Gibbs free energy (Delta GH) change approaches zero. Crystalline carbon materials possess limited active sites, with beta-graphyne showing the best Delta GH value of +0.34 eV. The adsorption study for MAC was conducted in 30 distinct local environments, where core structural properties were analyzed against varying radii. Calculations showed a Delta GH distribution for MAC ranging from -0.02 eV to +1.35 eV. To evaluate activity across the entire MAC surface, a MACE MLIP foundation model was finetuned, achieving optimal energy and force fitting of 1.67 meV/atom and 29.15 meV/A, respectively. The MLIP predicted Delta GH values from -0.91 eV to +1.70 eV, with approximately 15% of sites exhibiting values below +0.25 eV. Feature analysis revealed that 7-membered rings, curvature, and ripple height enhance HER activity. Our findings suggest that, with careful optimization of local features, MAC can be tuned to compete with noble metal catalysts.
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Materials Science · Cross-listed from cond-mat.str-el

Emergent Dynamic Magnetic Ground State in a Mixed 3d/5d Heavy Fermion System CaCu3Ir4O12

J. Ming, Abhisek Bandyopadhyay, G. B. G. Stenning et al. (+5 more)

Quantum-disordered magnetic ground states are challenging to identify in three-dimensional (3D) oxides, where strong exchange pathways typically favour long-range magnetic order or spin freezing. The quadruple perovskite $\mathrm{CaCu_3Ir_4O_{12}}$, crystallizing in the cubic $Im\bar{3}$ structure, provides a 3D lattice where $\mathrm{Cu^{2+}}$ $3d$ moments are coupled to an extended Ir $5d$ network, offering a rare platform for probing quantum-disordered magnetism in a mixed $3d/5d$ electron system. Here, we combine bulk probes, including DC and AC magnetic susceptibility, and heat capacity measurements (down to $50~\mathrm{mK}$), along with the local microscopic probe muon spin relaxation ($\mu$SR) (down to $40~\mathrm{mK}$), to investigate the true magnetic ground state of $\mathrm{CaCu_3Ir_4O_{12}}$. Despite strong antiferromagnetic interactions ($\theta_{\mathrm{W}} \sim -200~\mathrm{K}$, with an applied-field dependence), no signature of long-range magnetic ordering or spin freezing is detected down to the lowest measured temperatures. Furthermore, our in-depth zero-field (ZF) and longitudinal-field (LF) $\mu$SR characterizations confirm strong quantum spin fluctuations and the truly dynamic nature of the local moments down to $40~\mathrm{mK}$. These results establish $\mathrm{CaCu_3Ir_4O_{12}}$ as a promising 3D quantum-disordered magnet and a well-characterized platform for exploring fluctuation-dominated states in correlated $3d/5d$ oxides.
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All authors J. Ming, Abhisek Bandyopadhyay, G. B. G. Stenning, M. T. F. Telling, N. N. Wang, G. Wang, J.-G. Cheng, D. T. Adroja

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

Noncollinear antiferromagnetic structure and physical properties of CrRhAs with distorted kagome lattice

Chenglin Shang, Daye Xu, Bingxian Shi et al. (+8 more)

CrRhAs was theoretically proposed to be a kagome metal with unusual magnetic ground states; however, little is known about its magnetic structure and physical properties experimentally. Here, we present an experimental investigation of CrRhAs with ZrNiAl-type structure and a distorted Cr kagome lattice. CrRhAs is an antiferromagnet with TN = 149 K. Powder neutron diffraction analysis reveals a noncollinear antiferromagnetic structure with propagation vector k = (1/3, 1/3, 1/2), which features a ferromagnetic second nearest neighbor coupling in the kagome plane that is different from the prediction in previous density functional theory calculations. Furthermore, CrRhAs exhibits anomalous electrical transport properties which are possibly related to multiband effects and strong spin fluctuations. For the temperature-dependent longitudinal resistivity h̊o}xx, it is semiconductinglike above TN and becomes metallic below TN . The Hall coefficients exhibit two sign changes near 70 and 300 K. Combined with the results of heat capacity measurements, a large Kadowaki-Woods ratio {\alpha} = 33.9 {\mu}{\Omega} cm mol2 K2/J2 is obtained. The above results suggest CrRhAs is a strongly correlated kagome metal with multiband and noncollinear magnetic structure features.
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All authors Chenglin Shang, Daye Xu, Bingxian Shi, Xuejuan Gui, Zhongcen Sun, Juanjuan Liu, Jinchen Wang, Hongxia Zhang, Hongliang Wang, Lijie Hao, Peng Cheng

Materials Science

Dislocations in (011)-oriented vertical Bridgman $\beta$-Ga$_2$O$_3$ substrates

Yongzhao Yao, Daiki Katsube, Hirotaka Yamaguchi et al. (+1 more)

Dislocation in (011)-oriented $\beta$-Ga$_2$O$_3$ substrates grown by the vertical Bridgman method was investigated using X-ray topography (XRT), combined with X-ray reticulography. Transmission XRT reveals dislocations lying on the (001) plane and extending along [010], forming arrays associated with domain boundaries. Dislocations on the (011) plane were also identified but differ from those responsible for line-shaped pits on (001) epilayers. Reflection XRT shows good agreement with transmission XRT and enables classification of dislocation types based on contrast features. Reticulography confirms domain boundaries with misorientation on the order of 1E-5 rad, providing insight into defect formation relevant to epi-growth and device performance.
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All authors Yongzhao Yao, Daiki Katsube, Hirotaka Yamaguchi, Yukari Ishikawa

Materials Science

Spin-lattice coupling enables adaptive adsorption in magnetically-driven electrocatalysts

Arnold Gaje, Lulu Li, Felipe A. Garcés-Pineda et al. (+14 more)

A major challenge in electrochemistry is to decouple the reactive intermediates of a catalytic cycle to optimise their energies independently. During the oxygen evolution reaction (OER), such energy interdependence results from the need to generate multiple adsorbates at the same site and sets the minimum overpotential. Here, we show that an external stimulus, such as a magnetic field, can relax the scaling relationships between intermediates during the OER. Spectroscopic measurements and Density Functional Theory simulations in Ni-Fe oxyhydroxides reveal that applying a magnetic field alters surface chemisorption and injects structural flexibility at the interface. We interpret these observations as a consequence of stimulated changes in the spin-lattice coupling, which allow access to quasi-degenerate oxygenated intermediates that modulate the reaction energy demands. Our findings redefine the scaling limitations as state-projected rather than intrinsic and establish external stimulation as a strategy to navigate multi-state energy landscapes in electrocatalysis and sensing applications.
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All authors Arnold Gaje, Lulu Li, Felipe A. Garcés-Pineda, Camilo A. Mesa, Ghazaleh Abdolhosseini, Aditya K. Kushwaha, Dora Zalka, Elzbieta Trzop, Nicolas Godin, Raffaella Torchio, María Escudero-Escribano, Eric Collet, Sixto Giménez, Niels Keller, José Ramón Galán-Mascarós, Núria López, Ernest Pastor

Materials Science

Revisiting Ferroelectricity Beyond Polar Space Groups

Yudi Yang, Changming Ke and Shi Liu

Ferroelectricity, a hallmark of spontaneous inversion-symmetry breaking, has been a central concept in condensed matter physics and functional materials research, yet recent discoveries are revealing that switchable polarization can emerge in forms far richer than allowed by the conventional symmetry-based paradigm. Fractional quantum ferroelectricity and ionic-conductor ferroelectricity challenge the long-standing association of ferroelectricity exclusively with polar space groups. In this Review, we reconcile these emerging phenomena within the Berry-phase modern theory of polarization. We emphasize that polarization in insulating periodic crystals is not a single-valued vector, but a multivalued lattice quantity defined modulo a polarization quantum. Consequently, nonpolar crystals may possess nonzero formal polarization, and adiabatic paths connecting symmetry-equivalent structures can produce quantized changes in polarization without violating symmetry principles. The symmetry of this multivalued formal polarization is governed by a generalized Neumann principle. We further show that the large polarization changes induced by long-range ion migration in both fractional quantum ferroelectrics and ionic-conductor ferroelectrics can be naturally understood through the topological definition of oxidation state, which links ionic transport to quantized charge transfer and polarization change. We discuss the physical accessibility of these unconventional polarization states, highlighting the roles of switching pathways, boundary conditions, and domain-wall dynamics, particularly in systems such as $\alpha$-In$_2$Se$_3$. Finally, we suggest that the most promising functionality of these materials may lie not in conventional bulk ferroelectric switching, but in the creation and control of charged interfaces and domain walls arising from discontinuities in formal polarization.
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Materials Science

Water adsorption on a model silicate surface: wollastonite (100)

Luca Lezuo, Andrea Conti, Alexander Hoheneder et al. (+7 more)

Water adsorption on silicate surfaces is a critical yet poorly understood process relevant to, e.g., mineral weathering and cement hydration. This study investigates the structure of water overlayers on a model calcium silicate, the lowest-energy (100) surface of wollastonite (CaSiO3). It combines atomically resolved non-contact atomic force microscopy (nc-AFM), acquired with qPlus sensors and functionalized tips in ultrahigh vacuum (UHV), with density functional theory (DFT) calculations employing the metaGGA r2SCAN+rVV10 functional. Adding incremental doses of water to the sample at cryogenic temperatures produces distinct structures governed by the competition between water-surface and water-water interactions. With two water molecules per surface unit cell, water-surface interactions dominate: In line with previous theoretical predictions, adsorbates follow the surface lattice. As the coverage increases, intermolecular hydrogen bonding competes with bonding to the surface, leading to the emergence of complex, coexisting patterns. While their small energy differences prevent an unambiguous identification of the most stable structure by DFT, the experimentally observed symmetries help constrain plausible structural models. Above a critical density of four water molecules per unit cell, water-water interactions prevail, and water clusters are formed. The results provide an atomic-scale framework for understanding water interactions with calcium silicate surfaces.
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All authors Luca Lezuo, Andrea Conti, Alexander Hoheneder, Elena Vaníčková, Domitilla Alessandra Aloi, Rainer Abart, Florian Mittendorfer, Michael Schmid, Ulrike Diebold, Giada Franceschi

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

Frustration of harmonic and solitonic helimagnetism on the body-centered tetragonal lattice of GdAlSi

Ryota Nakano, Rinsuke Yamada, Oleg I. Utesov et al. (+9 more)

The triangular lattice antiferromagnet (TLAF) with nearest-neighbor exchange interaction is a model platform in the field of frustrated magnetism. Here, anharmonic (`up-up-down') and harmonic (`120 degree') magnetic states compete, because the fundamental helimagnetic wave and its higher harmonic are degenerate in energy. We show that a body-centered tetragonal lattice (BCTL) can realize a similar frustration of harmonic and anharmonic helimagnetic states, and that the tetragonal magnetic Weyl semimetal GdAlSi realizes this scenario. In an applied magnetic field, resonant elastic X-ray scattering reveals a competition of harmonic cycloidal and solitonic double-Q states, well consistent with mean-field calculations. Our work provides a new paradigm for frustration physics in BCTL materials.
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All authors Ryota Nakano, Rinsuke Yamada, Oleg I. Utesov, Masaki Gen, Akiko Kikkawa, Hajime Sagayama, Hironori Nakao, Masashi Tokunaga, Taka-hisa Arima, Yoshinori Tokura, Se Kwon Kim, Max Hirschberger

Materials Science

Physics-informed operator learning for transferable energy-dissipative microstructure dynamics

Jie Xiong, Yue Wu, Xuewei Zhou et al. (+2 more)

Phase-field simulations provide mechanistic descriptions of microstructure evolution, but repeated high-fidelity integration over long horizons and broad parameter spaces remains computationally expensive. We present PFNet, a physics-informed neural operator framework that advances microstructural states by learning conditional evolution operators rather than direct correlations. PFNet combines a diffusion-inspired U-Net with periodic padding, entropy-based state conditioning and thermodynamic-parameter modulation to encode boundary consistency, instantaneous ordering state and changes in the free-energy landscape. For Cahn-Hilliard coarsening, PFNet achieves accurate one-step prediction and stable autoregressive rollouts across composition, gradient-energy coefficient, coarsening stage and morphology class, with errors concentrated near diffuse interfaces and topology-changing regions. The same framework extends to a four-channel martensitic-transformation benchmark without martensite-specific redesign. These results indicate that physics-informed operator learning can provide transferable surrogates for phase-field dynamics and broader energy-dissipative dynamical systems.
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All authors Jie Xiong, Yue Wu, Xuewei Zhou, Peishuo Zhao, Jiaming Zhu

Materials Science

Physics Aware Representation Learning on Electronic Charge Density for Materials Property Prediction

Kammampati Sai Kumar, Albert Linda, Shubham Kumar Maurya et al. (+1 more)

The fundamental quantity governing the mechanical and thermodynamic properties of a crystalline solid is its electronic charge density. Yet, its direct use for the rapid prediction of materials properties remains challenging due to its high dimensionality. Here, we present a physics-informed deep learning framework that directly predicts mechanical and thermodynamic properties from the three-dimensional electronic charge density derived from density functional theory (DFT). The proposed approach first utilizes a three-dimensional convolutional autoencoder for unsupervised dimensionality reduction, compressing a high-resolution charge-density grid (128 x 128 x 128) into a compact latent representation (16 x 16 x 16 x 16) while preserving physically meaningful features, as confirmed by negligible reconstruction errors across diverse crystal systems. The compressed latent-space representation of charge density is then used by two different regression models for property prediction: Light Gradient Boosting Machine (LightGBM) and Attention-based 3D Convolutional Neural Networks (Att CNN), and their performance is compared. Combining composition-based descriptors (Material Agnostic Platform for Informatics and Exploration or MAGPIE) with electronic charge density data further improves the model accuracy. Using a dataset of about 6059 inorganic compounds spanning multiple crystal symmetries, the models achieve strong predictive performance for bulk modulus K (R2 = 0.94), Young's modulus E (R2 = 0.88), shear modulus G (R2 = 0.87), formation energy Eform (R2 = 0.96), and Debye temperature {\Theta} (R2 = 0.89). This work establishes electronic charge density as a transferable, physics-grounded descriptor for materials property prediction, requiring ~ 1/25 the computational resources of full-fledged DFT calculations.
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All authors Kammampati Sai Kumar, Albert Linda, Shubham Kumar Maurya, Somnath Bhowmick

Materials Science

Fine-tuning a vision-language model for fracture-surface morphology recognition

Quanliang Liu, Jungtaek Kim, Kangwook Lee et al. (+1 more)

Vision-language models (VLMs) have shown strong potential for scientific image understanding, but general-purpose models often lack the domain-specific visual knowledge required for reliable materials characterization. In this work, we fine-tuned an open-source VLM (Qwen3-VL-32B-Instruct) for fracture-surface image analysis using a curated dataset of 13,168 open-source, literature-mined fracture-surface images. Morphology annotations were generated by GPT-5.2-Reasoning (high) from both the images and relevant excerpts of their source papers, and the dataset was further enriched with targeted manual collection and rotation-based augmentation. The resulting specialist model outperforms flagship proprietary multimodal models on a benchmark of 100 manually annotated images. It achieves a precision of 0.92, compared to 0.35 for the base Qwen3-VL-32B-Instruct, 0.58 for GPT-5.5-Reasoning (high), and 0.78 for Gemini 3.1 Pro-Reasoning (high). Dataset ablations show that manual collection of rare-feature images and augmentation via image rotation are both beneficial to improve recognition of less common fracture morphology features. We further discuss integrated use of the fine-tuned model with proprietary models to combine fracture-specific visual accuracy with broader multimodal reasoning for autonomous fractography. Although focused on fracture-surface images, this work demonstrates how VLMs can be adapted through targeted collection and fine-tuning on novel feature images to recognize those features and support downstream decision-making in autonomous microscopy workflows.
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All authors Quanliang Liu, Jungtaek Kim, Kangwook Lee, Hyunseok Oh

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

Revisiting magnetoelectric response in collinear antiferromagnetic zigzag chains: A downfolding approach beyond conventional low-energy models

Shuhei Kanda and Satoru Hayami

Magnetoelectric (ME) effects in antiferromagnets provide a fertile platform for exploring symmetry-driven cross-correlated responses. However, their microscopic origin remains elusive and is often obscured in simplified low-energy descriptions. In this study, we revisit the microscopic mechanism of the ME effect in a collinear antiferromagnetic zigzag chain by employing a multi-orbital tight-binding model that explicitly includes both $s$- and $p$-orbital degrees of freedom. Using analytical and numerical calculations based on the Kubo formula, we demonstrate that the ME response is governed by orbital degrees of freedom activated through $s$–$p$ hybridization, while the spin contribution vanishes due to spin conservation. To elucidate the low-energy description, we derive an effective Hamiltonian projected onto the $s$-orbital subspace using the Schur complement. We show that a naive application of the Kubo formula within this effective model fails to capture the ME response. This issue is resolved by systematically incorporating vertex corrections in terms of orbital hybridization into the response functions. Furthermore, by introducing a quasiparticle renormalization scheme, we formulate a renormalized Kubo formula that preserves conservation laws and accurately reproduces the full multi-orbital results. Our analysis revisits the conventional low-energy perspective and reveals that the ME effect originates from virtual interorbital processes encoded in vertex corrections, rather than from the bare low-energy Hamiltonian. The effective framework developed here provides a unified microscopic understanding of orbital-driven ME responses and offers a systematic route to incorporate hybridization effects beyond simple low-energy models.
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Thursday 7 May

Materials Science

SLayerGen: a Crystal Generative Model for all Space and Layer Groups

Rees Chang, Andrew Novick, Ryan P Adams et al. (+1 more)

Crystal generative models have shown rapid progress for accelerating the discovery of bulk, periodic materials. However, many material systems such as 2D superconductors, thin film semiconductors, and catalytic surfaces are diperiodic, i.e., aperiodic along one of the lattice directions. These systems are invariant under the layer groups, which are known to influence materials properties yet not considered by existing models. In this paper, we propose SLayerGen, a generative model that produces crystals constrained to be invariant to any space or layer group. SLayerGen consists of coarse-to-fine discrete autoregressive lattice generation; transformer-based autoregressive sampling of Wyckoff positions, elements, and numbers of symmetrically unique atoms; and space or layer group equivariant diffusion of atomic coordinates. For the diffusion component, we corrected an inconsistency in the loss from prior work arising from hexagonal groups being non-orthogonal in fractional coordinates. To facilitate progress in generative modeling of diperiodic materials, we assembled and filtered datasets of monolayers and bilayers, propose relevant evaluation metrics, and developed novel representations for layer group symmetries. For de novo generation of diperiodic materials, SLayerGen achieves consistent performance gains over bulk crystal generative models and is competitive when training jointly on bulk and diperiodic materials.
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All authors Rees Chang, Andrew Novick, Ryan P Adams, Elif Ertekin

Materials Science

Two-dimensional clay channels for tunable nanofluidic memristor

Sangeeta Yadav, Raj Kumar Gogoi, Aziz Lokhandwala et al. (+4 more)

Dynamic reconfiguration of charge carriers in confined ion-channels under electrical stimulation produces memory effects, where the internal resistance depends on history of the electric field. Vermiculite nanofluidic devices harness this effect to store and process information within a single component. We report switching between distinct memory loops by tuning ion transport pathways, governed by asymmetrical device architecture and intrinsic surface-charge. Polarity-dependent memory switching between crossing-1 and crossing-2 loops is achieved solely by altering electrode configurations, without modifying electrolyte, channel surface chemistry or device structure: providing mechanistic insights into ionic memristors through a straightforward, experimental strategy. The memristive characteristics are demonstrated in both in-plane and out-of-plane channel configurations with channel lengths spanning from centimeters to micrometers length scales using re-stacked vermiculite membranes and further investigated for miniaturization with devices of nanometer scale channel lengths, fabricated via ultramicrotomy method. Furthermore, we demonstrate neuromorphic functionalities, including synaptic potentiation-depression and programmable memory retention, highlighting potential for bio-inspired computing systems. Cost-effective and scalable fabrication solution processed vermiculite membrane memristors pave the way for practical integration of nanofluidic memristors for neuromorphic computing applications.
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All authors Sangeeta Yadav, Raj Kumar Gogoi, Aziz Lokhandwala, Siddhi Vinayak Pandey, Ankit Bhardwaj, Sunando DasGupta, Boya Radha

Materials Science · Cross-listed from cs.LG

Can LLMs Predict Polymer Physics Just by Reading Synthesis and Processing Prose?

Yuchu Liu, Rui Zhu, Jingwei Xiong et al. (+1 more)

Can large language models predict physical and mechanical polymer properties simply by reading unstructured scientific prose? Polymer performance is rarely determined by chemical structure alone; identical nominal polymers can exhibit drastically different behaviors depending on their synthesis route, processing history, morphology, and testing conditions. Yet, state-of-the-art polymer property models typically rely on structure-only representations – such as SMILES or molecular graphs – which strip away this vital experimental context. In this work, we introduce PolyLM, a natural-language-only, process- and condition-aware framework that predicts materials performance directly from full-text literature. By circumventing structural inputs entirely, PolyLM preserves the nuanced, unstructured descriptions of synthesis and processing reported by domain scientists. To train this framework, we curated an unprecedented, literature-scale dataset encompassing 185,000 scientific papers and over 276,400 unique polymer samples across 22 physical, mechanical, and thermal properties. We fine-tuned a massive 9-billion-parameter language model (Qwen3.5-9B) using Low-Rank Adaptation (LoRA) and task-level uncertainty weighting. Evaluated on 68,283 held-out observations, the model achieves remarkably high predictive accuracy, establishing new state-of-the-art benchmarks for complex properties. Across the 22 diverse targets, the model achieves a median $R^2$ of 0.74, with predictions for key thermal, mechanical, and physicochemical properties frequently surpassing an $R^2$ of 0.80. These results unequivocally demonstrate that natural language is a powerful, highly scalable interface for realistic materials performance prediction.
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All authors Yuchu Liu, Rui Zhu, Jingwei Xiong, Haixu Tang

Materials Science

Exploring the Potential of Ternary Blending for Two and Three-Junction RAINBOW Solar Cells

Francesc Xavier Capella-Guardià, Jolanda Simone Müller, Muhammad Ahsan Saeed et al. (+7 more)

The efficiency of organic photovoltaics (OPV) has been steadily increasing over the past decade until reaching the 20% milestone. Multijunction architectures provide a promising approach to further enhance performance. Here we explore the potential of a spectral splitting geometry, referred to as RAINBOW, in which subcells are placed side-by-side and externally connected, thus minimizing the fabrication and current matching challenges found in vertically stacked configurations. First, we tested 7 different binaries with bandgaps spanning from 1.98 to 1.16 eV. The systems with the widest and narrowest gaps suffered greater losses and so we evaluate if ternary mixing could help to overcome these limitations by evaluating 5 different ternaries. Generally speaking, ternary mixing tunes the Voc, and when morphology and energy levels are well aligned, the overall PCE can be boosted in the spectral region where the subcell should absorb, as is the case for PTB7-Th:COTIC-4F:BTP-eC9 when operating as red subcell. Device simulations help to identify the 2-junction and 3-junction configurations with highest PCEs, all of which include ternaries. We fabricate proof-of-concept RAINBOW devices using scalable methods in which the subcells are deposited by meniscus-guided blade coating. The efficiency improves from 12.9% in single-junction devices to 15.9% in 2-junction devices (16.4% in simulations) and 17.3% in 3-junction devices (17.7% in simulations), confirming the viability of the RAINBOW architecture for scalable, high-efficiency OPVs. Finally, detailed balance analysis indicates that the potential of this geometry can be very high provided that high efficiency wide bandgap (2-2.5 eV) materials become available.
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All authors Francesc Xavier Capella-Guardià, Jolanda Simone Müller, Muhammad Ahsan Saeed, Xabier Rodríguez-Martínez, Miquel Casademont-Viñas, Albert Harillo-Baños, Jaime Martín, Jenny Nelson, Alejandro R. Goñi, Mariano Campoy-Quiles

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

Nonadiabatic Theory of Phonon Magnetic Moments in Insulators and Metals

Haoran Chen, Wenqin Chen, Kaijie Yang et al. (+2 more)

We develop a nonadiabatic theory of phonon magnetic moments applicable to both insulators and metals. By relating the phonon magnetic moment to the force-velocity response of ions in a magnetic field, we derive a gauge-invariant expression using a gauge-covariant Wigner expansion. The formalism naturally separates Fermi-sea and Fermi-surface contributions and captures the full dependence on phonon frequency. In gapped systems, our theory reduces to previous adiabatic expressions in the low-frequency limit. Beyond this limit, it reveals additional contributions arising from resonant interband processes and the Fermi surface. Applying our theory to Pb$_{1-x}$Sn$_x$Te, we find that the Fermi-surface contribution substantially enhances the phonon magnetic moment, reproducing the same order of magnitude as the experimental observation. Our results provide a unified framework for describing phonon magnetic moments beyond the adiabatic regime.
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All authors Haoran Chen, Wenqin Chen, Kaijie Yang, Ting Cao, Di Xiao

Materials Science

LLM-Guided Open Hypothesis Learning from Autonomous Scanning Probe Microscopy Experiments

Boris Slautin, Utkarsh Pratiush, Yu Liu et al. (+2 more)

Autonomous experimentation has transformed microscopy and materials discovery by enabling closed-loop optimization including imaging and spectroscopy tuning, strucutre property relationship discovery, and exploration of combinatorial libraries. However, most current workflows remain limited to selecting measurements within fixed objective or hypothesis spaces, rather than generating new physical models from experimental data. Here, we introduce an open hypothesis-learning framework that combines symbolic regression with large-language-model-based physical evaluation and implement it for autonomous scanning probe microscopy. Symbolic regression generates candidate analytical relationships directly from sparse measurements, while the language-model evaluator ranks these candidates according to physical plausibility, scaling behavior, and consistency with known mechanisms. We demonstrate the approach on autonomous piezoresponse force microscopy measurements of ferroelectric domain switching in a PZT thin film. Starting from five seed measurements, the workflow evolves from physically incomplete candidate expressions toward interpretable voltage-time growth laws consistent with kinetic domain-wall motion. This work extends autonomous microscopy from closed-loop optimization toward open hypothesis discovery, where candidate physical laws emerge from the experiment itself rather than being specified in advance. More broadly, the framework establishes a route for integrating symbolic regression, physical reasoning, and adaptive experimentation into hierarchical autonomous scientific workflows.
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All authors Boris Slautin, Utkarsh Pratiush, Yu Liu, Kamyar Barakati, Sergei Kalinin

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

Disentangling bulk and surface electronic structure using targeted cleave planes in RuO$_2$

Maria H. Visscher, Sebastian Buchberger, Bruno Saika et al. (+6 more)

Rutile RuO$_2$ has attracted significant interest due to its putative unconventional electronic and magnetic properties and its proximity to superconductivity. However, the measurement and interpretation of its electronic structure has been complicated by a strongly three-dimensional crystal structure. Here, we demonstrate how the preparation of targeted $(110)$ and $(100)$ surfaces via focused ion beam (FIB)-engineered cleaving allows the acquisition of high-quality measurements of the electronic structure using angle-resolved photoemission spectroscopy. Our results demonstrate that ARPES spectra of RuO$_2$ are, in fact, largely dominated by signatures of distinct surface electronic states. From comparison with density-functional theory, we resolve a surface termination-dependent variation of these, and disentangle them from highly-three-dimensional bulk states and surface resonances. Moreover, we find a marked role of the substantial spin-orbit coupling of the Ru 4$d$ orbitals in the surface region, where a breaking of spatial inversion symmetry leads to significant Rashba-type spin splittings of the surface bands.
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All authors Maria H. Visscher, Sebastian Buchberger, Bruno Saika, Shu Mo, Lea Richter, Mats Leandersson, Craig Polley, Andrew P. Mackenzie, Phil D. C. King

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

Direct Experimental Test of Conformal Invariance via Grazing Scattering: A Proposal for X-ray and Neutron Experiments

Alessandro Podo and Slava Rychkov

We propose a test of conformal invariance in critical phenomena based on the study of a two-point correlation function in the presence of a boundary. This two-point function can be studied using X-ray or neutron scattering in the conditions of total reflection (so-called grazing scattering). The conformal Ward identity in momentum space is here expressed as a differential constraint on the scattering cross-section, as a function of the momentum transfer and the scattering angle. Experimental verification using X-rays and binary alloys appears well within the existing techniques, while feasibility for neutron scattering requires further study. This would be the first direct experimental test of conformal invariance in critical phenomena, a symmetry widely assumed but never directly verified.
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