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Physics Condensed Matter Materials Science

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Tuesday 21 April

Materials Science

Operando Characterization of Volume Changes in Lithium-Ion Battery Electrodes during Cycling using Isotope Multilayers

Erwin Hueger, Daniel Uxa, Lars Doerrer et al. (+2 more)

This study reports on advancements in operando characterization of volume changes in lithium-ion battery (LIB) electrode materials during electrochemical cycling. Volume changes are crucial for LIB operation because they are related to the amount of stored energy as well as LIB integrity, performance, and safety. The study introduces a method based on isotope multilayers as active material to track the intrinsic modification of electrode volume in real time under operating conditions with operando neutron reflectometry. A natGe-73Ge multilayer film is used as a model system to measure the volume change of amorphous germanium electrodes during charging and discharging. Isotope modulation produces a Bragg peak in the neutron reflectivity pattern, sensitive only to the modification of volume within the active material of the electrode. Battery side reactions, such as the growth and reduction of the solid-electrolyte interphase is excluded. Using this method, the volume modification as a function of Li content x in LixGe can easily be derived from the scattering vector position of the Bragg peak without fitting numerous complex reflectivity patterns. The experiments show a reversible volume change of amorphous germanium of up to 250 percent for x = 3, which appears to be largely independent of current density, cycle number, and the thickness of the individual Ge layers. Also, there are tentative indications that the crystallization and re-amorphization of LixGe are not influencing the volume change.
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All authors Erwin Hueger, Daniel Uxa, Lars Doerrer, Jochen Stahn, Harald Schmidt

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

Termination-Controlled Fractionalization and Hybridization at Topological Interfaces in Organic Spin Chains

Khalid N. Anindya and Hong Guo

A single organic spin platform hosts both dimerized $S=\tfrac{1}{2}$ and effective Haldane $S=1$ sectors, linked by bond-texture inversion. At the junction, the fractional mode is controlled by termination parity: quenched by local fusion at one termination and released as an uncompensated spin-$\tfrac{1}{2}$-like degree of freedom at the parity-shifted one. Two such internal boundary modes of a finite embedded Haldane domain hybridize with an exponentially decaying splitting, establishing termination parity as a design principle for engineering and coupling fractional boundary modes.
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Materials Science · Cross-listed from cond-mat.supr-con

Competing Constraints on Superconductivity in Thick FeSe films

Ya-Xun He, Xing-Jian Liu, Qun Wang et al. (+6 more)

Superconducting films emerge from the complex interplay of multiple growth parameters, making their optimization challenging. In iron-based superconductors, compressive strain is known to enhance the transition temperature (Tc) of FeSe films, yet reported Tc values vary widely even on identical substrates, indicating factors beyond strain are critical. Here, we develop a high-throughput off-center pulsed laser deposition strategy that transforms plume inhomogeneity into combinatorial FeSe film libraries with continuous gradients in lattice parameter, composition, and disorder. We discover that the maximum Tc does not coincide with the plume center but can shift off-center, revealing a competition between favorable c-axis expansion, stoichiometry, and defect scattering. Systematic characterization of 80 thick films (>50 nm), combined with interpretable machine learning, shows that besides the strong correlate of c-axis lattice parameter to Tc, the stoichiometry and disorder scattering impose critical constraints on the achievable transition temperature, defining a narrow optimization window rather than a simple monotonic relationship. This framework yields Tconset=17.1 K in thick FeSe films and establishes a general framework combining combinatorial synthesis with machine learning to uncover constrained optimization landscapes in complex functional materials.
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All authors Ya-Xun He, Xing-Jian Liu, Qun Wang, Ting Chen, Hassan Ali, Jia-Ying Zhang, Bao-Juan Kang, Zheng Zhang, Jun-Yi Ge

Materials Science · Cross-listed from physics.optics

Fast projections of two-dimensional light patterns using acousto-optical deflectors

Robbert Decruyenaere, Clara Tanghe, Senne Van Wellen et al. (+1 more)

Precise and flexible control of structured light fields is essential for applications ranging from optical trapping and quantum simulation to microscopy and materials processing. Acousto-optical deflectors (AODs) are widely used in these settings due to their high speed, large damage threshold, and ability to generate steerable optical tweezers. Multi-tone driving offers a powerful alternative to slow sequential scanning, enabling the projection of complex patterns with high accuracy as rapid acoustic modulation averages out inter-spot interference. In two dimensions, however, intermodulation between tones in orthogonal AODs can reintroduce coherent artifacts. We present a fast, feedback-free AOD projection scheme based on an incommensurately staggered frequency lattice that intrinsically suppresses such artifacts. For separable two-dimensional target patterns, our method removes the need for scanning entirely, enabling substantially faster and highly accurate projections. We further extend the approach to non-separable images using a minimal scanning strategy that maintains rather high projection speeds. These results demonstrate that appropriately engineered multi-tone AOD driving offers an efficient and robust route to high-speed, high-fidelity generation of arbitrary intensity patterns.
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All authors Robbert Decruyenaere, Clara Tanghe, Senne Van Wellen, Karel Van Acoleyen

Materials Science · Cross-listed from physics.ins-det

Drift Correction of Scan Images by Snapshot Referencing

Zac Thollar, Kanto Maeda, Tetsuya Kubota et al. (+3 more)

Reliable quantitative analysis in scanning (transmission) electron microscopy (S(T)EM) is often hindered by image drift during long-duration spectral mapping for elemental analysis or for various material functions. We here present snapshot-referencing (SSR) drift correction, a retrospective approach to eliminate spatial distortion based on the temporal nature of the scanning process. A continuous drift vector for every pixel is calculated for a normalized time-field of the scan pattern (e.g., serpentine or raster) utilizing a high-signal, fast-scan "snapshot" as a drift-free reference to guide the correction of simultaneously acquired analytical maps. To describe the drift, we employed Bezier basis functions to model smooth thermal or mechanical drifts and piece-wise linear basis for high-frequency "spiky" shifts such as those caused by charging. We demonstrate the efficacy of this approach on experimental cathodoluminescence (CL) datasets, showing that it effectively restores spatial integrity to hyperspectral data cubes without the need for specialized hardware. This flexible, software-based solution is broadly applicable to any probe-based analytical technique where a fast imaging signal can be recorded alongside slow spectroscopic data.
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All authors Zac Thollar, Kanto Maeda, Tetsuya Kubota, Taka-aki Yano, Qiwen Tan, Takumi Sannomiya

Materials Science

Multimodal Transformer for Sample-Aware Prediction of Metal-Organic Framework Properties

Seunghee Han, Jaewoong Lee and Jihan Kim

Metal-organic frameworks (MOFs) are a major target of machine-learning-based property prediction, yet most models assume that a single framework representation maps to a single property value. This assumption becomes problematic for experimental MOFs, where samples reported as the same framework can exhibit different properties because of differences in crystallinity, phase purity, defects, and other sample-dependent factors. Here we introduce Experimental X-ray Diffraction Integrated Transformer (EXIT), a multimodal transformer for sample-aware prediction of MOF properties that combines MOFid with X-ray diffraction (XRD). In EXIT, MOFid encodes MOF identity, whereas XRD provides complementary information about the experimentally realized sample state. EXIT is pre-trained on one million hypothetical MOFs with simulated XRD to learn transferable representations, leading to improved downstream performance relative to existing approaches. EXIT is fine-tuned on literature-derived experimental datasets for surface area and pore volume prediction. Incorporating experimental XRD improves predictive performance relative to models without experimental XRD, and attention analysis and sample-level case studies further show that EXIT assigns different predictions to samples sharing the same MOF identity when their XRD patterns differ. These results establish a practical step from framework-aware to sample-aware MOF property prediction and highlight the value of incorporating experimental characterization into porous materials informatics.
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Materials Science

True random number generation through stochastic magnonic bistability

Mengying Guo, Zhenyu Zhou, Denys Slobodianiuk et al. (+13 more)

True random number generators (TRNGs) underpin modern cryptography, yet existing implementations face fundamental trade-offs between speed, scalability, and entropy quality. Here, we demonstrate that stochastic switching in the bistable regime of spin-wave dynamics provides a physical entropy source for high-quality random number generation. Our magnonic random number generator (mRNG), based on a lithography-patterned microstrip on yttrium iron garnet (YIG), exploits thermal fluctuations near the nonlinear bistable regime to generate random bitstreams that pass all 15 NIST SP 800-22 statistical tests at rates with 20 Mb/s. We implement a random-bit multiplier using synchronized mRNG units and demonstrate scalability to 200-nm-wide nanoscale waveguides, establishing spin-wave bistability as a viable physical entropy source for integrated random number generation.
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All authors Mengying Guo, Zhenyu Zhou, Denys Slobodianiuk, Roman Verba, Kristýna Davídková, Xueyu Guo, Xudong Jing, Yueqi Wang, Björn Heinz, Yiheng Rao, Carsten Dubs, Caihua Wan, Xiufeng Han, Andrii V. Chumak, Philipp Pirro, Qi Wang

Materials Science

Electrically steered conduction topologies and period-doubling phase dynamics in VO2

Siyuan Huang, Shuaishuai Sun, Yin Shi et al. (+6 more)

The insulator-to-metal transition (IMT) in strongly correlated materials, such as vanadium dioxide (VO2), offers a transformative platform for next-generation adaptive electronics and neuromorphic computing. However, harnessing this non-equilibrium phase transition for deterministic device operation is fundamentally hindered by the inability to disentangle electric-field effects from Joule heating, owing to a lack of operando techniques capable of resolving phase dynamics at nanoscale spatial and sub-nanosecond temporal scales. Here, using a newly developed electrical-pulse-pump ultrafast transmission electron microscope (E-UTEM), we directly visualize the multi-scale electro-thermo-mechanical dynamics of the IMT in suspended VO2 devices. Our results reveal that electric-field-induced Poole-Frenkel (PF) emission, localized by patterned oxygen vacancies, plays a decisive role in redistributing the internal electric field to trigger a deterministic Mott transition. The extreme non-linearity of this PF effect enables the formation of dynamically reconfigurable connectivity topologies that bypass conventional thermal limits. Furthermore, we observe that the coupling of thermal and elastic energies governs a discrete domain evolution, characterized by step-wise and period-doubling configurational resets, which is a hallmark of non-equilibrium phase dynamics in constrained geometries. By integrating experimental imaging with phase-field simulations, we establish a comprehensive framework for the electrically-driven IMT and predict sub-100-ps switching kinetics. These findings provide a fundamental basis for the rational design of ultrafast, low-energy functional devices through nanoscale defect and strain engineering in correlated systems.
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All authors Siyuan Huang, Shuaishuai Sun, Yin Shi, Wentao Wang, Chunhui Zhu, Huanfang Tian, Huaixin Yang, Jun Li, Jianqi Li

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

Intra- and Interlayer Excitonic Fine Structure of the Two-Dimensional Perovskite (PEA)$_2$PbI$_4$

Patrick Grenzer, Fabian Lie, Klaus H. Eckstein et al. (+2 more)

Two-dimensional halide perovskites host strongly bound excitons whose fine structure controls polarization selection rules and radiative recombination, yet several spectral features in (PEA)$_2$PbI$_4$ remain controversially assigned. Here, polarization-resolved low-temperature photoluminescence combined with first-principles G$_0$W$_0$+BSE calculations resolves both the intralayer and interlayer excitonic fine structure of this prototypical n=1 Ruddlesden-Popper perovskite. The low-energy multiplet is consistently described as a purely excitonic intralayer fine structure governed by crystal symmetry, octahedral distortions, and the two-layer unit cell, without invoking Rashba or exciton-polaron mechanisms as the primary origin. A weaker doublet ~45 meV above the bright intralayer states is identified as interlayer excitons from its agreement with the calculated interlayer manifold in energy and splitting. Although the static calculations underestimate their oscillator strength and do not reproduce the observed orthogonal polarizations, distortion-induced mixing with bright intralayer excitons strongly enhances interlayer optical activity and provides a plausible explanation for their visibility. Our results establish interlayer excitons in (PEA)$_2$PbI$_4$ and refine the excitonic description of fine structure in two-dimensional perovskites.
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All authors Patrick Grenzer, Fabian Lie, Klaus H. Eckstein, Tobias Hertel, Linn Leppert

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

Perspective: Quantum Computing on Magnetic Racetrack

Ji Zou, Jelena Klinovaja and Daniel Loss

Magnetic domain walls have long been pursued as carriers of classical information for storage and processing. With the ability to create, control, and probe domain walls at the nanoscale, they are recently recognized as an ideal platform for studying macroscopic quantum effects and provide a natural blueprint for building scalable quantum computing architectures. In particular, the experimentally demonstrated high mobility of domain walls makes them not only suitable as stationary qubits but also as flying qubits, which may offer advantages over currently explored quantum computing platforms. In this Perspective, we outline our current understanding of the essential ingredients and key requirements for realizing universal quantum computation based on magnetic domain walls. We highlight promising concrete material platforms and identify the experiments that are still needed to advance this concept. We also discuss the potential challenges and point to new opportunities in this emerging research direction at the interface between magnetism and quantum information science.
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Materials Science · Cross-listed from physics.med-ph

Corneal deformation mapping and FE-based strain analysis via digital image correlation: biomechanical changes after CXL and laser refractive surgery

Benedetta Fantaci, Alejandro Frechilla, Matteo Frigelli et al. (+3 more)

Accurate assessment of corneal mechanical properties is critical for understanding ocular biomechanics, predicting refractive surgery outcomes, and optimizing cross-linking (CXL) treatments. Conventional uniaxial tensile test is limited by non-physiological boundary conditions and simplified stress distributions. Inflation testing more closely reproduces the in vivo stress state but has traditionally lacked full-field deformation mapping. In this work, we present an integrated experimental-computational protocol combining inflation testing of freshly enucleated porcine eyes with high-resolution three-dimensional digital image correlation (3D-DIC). Fifteen corneas were analyzed across three cohorts: (i) de-epithelialized controls, (ii) CXL-treated (standard Dresden protocol), and (iii) anterior stromal ablation via femtosecond laser. Samples were subjected to controlled intraocular pressure (IOP) elevations up to 40 mmHg. The 3D-DIC approach provided dense, pointwise displacement and strain maps across the anterior surface, successfully quantifying the localized stiffening effects of CXL and the increased compliance induced by stromal ablation. These full-field kinematic data were integrated into a membrane-theory finite element framework to resolve principal in-plane strains, that were used for subsequent inverse modeling to derive anisotropic hyperelastic parameters of porcine corneal tissue. Overall, the method establishes an end-to-end route from physiologic loading to full-field strain mapping and constitutive parameter identification, enabling quantitative evaluation of treatment-induced biomechanical changes in the cornea.
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All authors Benedetta Fantaci, Alejandro Frechilla, Matteo Frigelli, Philippe Büchler, Sabine Kling, Begoña Calvo

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

Unveiling the Superconducting Ground State of Heusler alloy Pd2ZrIn via muon spin relaxation and rotation measurement

Kavita Yadav, Anoop M Divakaran, Tsunehiro Takeuchi et al. (+1 more)

Full Heusler alloys XInPd2 (X= Zr, Hf and Ti) have recently attracted significant attention owing to their symmetry-driven electronic structure and also due to the interplay between disorder and emergent ground states. Within this family, Pd2ZrIn serves as a unique platform to study the effect of disorder on superconducting pairing. This alloy crystallizes in a cubic L21 structure with significant B2-type antisite disorder. Electrical resistivity and magnetic susceptibility studies confirm bulk type-II superconductivity with a transition temperature TC ~ 2.2 K. Zero-field {\mu}SR results reveal no evidence of spontaneous internal magnetic fields below TC, confirming the preservation of time-reversal symmetry. Transverse-field {\mu}SR spectra show the formation of a vortex lattice, consistent with type-II superconductivity, and the superfluid density is well described by a fully gapped, nodeless s-wave state with superconducting gap {\Delta} (0) ~ 0.33 \pm 0.01 meV. Furthermore, the estimated ratio of transition temperature and Fermi temperature (TC/TF) indicates that this alloy lies within the conventional superconducting regime on the Uemura plot. These results establish Pd2ZrIn as a weakly coupled, dirty-limit, type-II superconductor; with a fully gapped, nodeless order parameter and preserved time-reversal symmetry.
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All authors Kavita Yadav, Anoop M Divakaran, Tsunehiro Takeuchi, K. Mukherjee

Materials Science

Rippled graphene pores as fluidic memristive devices with synaptic and neuromorphic functionalities

Wenzhe Zhou, Dongjiao Ge, Ao Zhang et al. (+8 more)

Nanofluidic memristive devices work with nanoscale pores and ions dissolved in water, which harness the ionic memory effect aiming to store and process information. These devices share the same charge carriers as biological systems and bring hope for better emulating the neural functions and developing ionic circuits for neuromorphic applications. Specially, theory and experiments suggest that nanoconfinement is essential for inducing a memory effect, which places limit on the pore size to nm-scale or smaller. Such devices are difficult to scale up with precision and operate with long-term stability. Here, we show that a micrometer size pore, generally expected to exhibit a linear ion transport, can display a pronounced memory effect, if its rim is wrapped by strongly curved and tightly stacked graphene. We attribute the observation to slow ion dynamics confined in the rippled graphene edges. The devices are easy to scale up and integrate into fluidic circuits. The memory effect is ion-selective and exhibits long endurance comparable to the lifetime of synaptic proteins, which enables reversible modification of the conductance states using programmable voltage spikes and various electrolytes over a long time, akin to biological synaptic plasticity. Thanks to this plasticity, our devices and their integrated circuits enable storing, transmitting and processing information with high reliability, fidelity and accuracy, as evidenced in the identification of both greyscale and color images, and in the real-time analysis of emulated neural signals. Our results highlight nanoscale morphology of the pore wall as an important parameter regulating ion transport and indicate that the stringent nanoconfinement for ionic memory can be lifted from restricting the pore size to designing its rim structure. The devices and their integrated circuits may find use in ionic neuromorphic applications.
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All authors Wenzhe Zhou, Dongjiao Ge, Ao Zhang, Jincheng Xu, Yu Ji, Yiran Gong, Wenchang Zhang, Jidong Li, Li Lin, Zhiping Xu, Pengzhan Sun

Materials Science

From Entropy to Compression: Competing Thermodynamic Drivers of Structural Transitions in Transition Metals

S. Azadi, S.M. Vinko, A. Principi et al. (+2 more)

Solid-solid phase transitions in metals are traditionally driven by changes in density or external pressure. Here we show that, under strong electronic excitation, structural stability is governed by the interplay between electronic effects and compression. Using finite-temperature density functional theory, we construct pressure-temperature phase diagrams for 15 metals spanning hcp-, fcc-, and bcc-ground-state structures. The results reveal a systematic reduction of structural diversity with increasing electronic temperature, with stability increasingly dominated by the fcc structure, while hcp remains a persistent secondary phase and bcc stability is progressively suppressed. At elevated temperatures, fcc is broadly favored, whereas bcc is stabilized primarily by compression, leading to a material-dependent competition across the periodic table. These findings provide a unified framework for understanding structural transformations in electronically excited metals and highlight the importance of considering both electronic excitation and pressure in describing phase stability far from equilibrium.
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All authors S. Azadi, S.M. Vinko, A. Principi, T.D. Kuehne, M.S. Bahramy

Materials Science

Controlling Quantum Materials by Growth: Thermodynamics, Kinetics, and Defect Engineering in Transition Metal Dichalcogenides

Anzar Ali, Md Ezaz Hasan Khan and Mahmoud Abdel-Hafiez

Transition metal dichalcogenides exhibit a wide range of semiconducting, metallic, correlated, and topological electronic states that arise from strong coupling between lattice structure, dimensionality, and electronic degrees of freedom. In these materials, crystal growth is not merely a preparative step but a thermodynamic boundary condition that establishes chemical potentials, defect populations, polytype stability, and access to metastable phases. As a result, synthesis determines the structural and defect landscape from which collective electronic behavior emerges. In this Review, we develop a unified thermodynamic and kinetic framework that connects growth conditions to phase stability, defect energetics, and microstructure. We examine how chemical potential constraints define stability windows, how supersaturation and mass-transport regimes govern nucleation and morphology, and how nonequilibrium pathways enable kinetic trapping and polymorph selection. Bulk and thin-film synthesis approaches, including chemical vapor transport, flux growth, physical vapor transport, solvent-assisted crystallization, chemical vapor deposition, and molecular beam epitaxy, are placed within a common thermodynamic and kinetic map to clarify how distinct growth regimes produce characteristic disorder profiles and structural phases. By explicitly linking synthesis variables to charge-density-wave order, superconductivity, band topology, and correlation effects, this Review establishes crystal growth as a central parameter in determining the effective electronic Hamiltonian realized in experiment. This perspective provides a physically grounded framework for improving reproducibility and guiding deterministic control of emergent quantum phases in layered materials.
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Materials Science

Discovery of Graphene Sheets and C-Rich Micro-Oval structure in Stingless Bee Hive; Leading to an Emergent Material with Debut of Blue Emission

Manas Kumar Dalai, Ankita Mahakhuda and Abinash Prusty

Naturally produced stingless bee hive (NP-SBH) is an intricately produced material by the combination of waxes, resin and other biological materials that offers protection and structural stability to the bee colony. This study explores a detailed analysis of Indian stingless bee hive material using multi-characterization techniques approach to evaluate their morphological, ultrastructural, chemical composition and their crystallinity. FESEM reveal uniformly distributed micro-oval structures along with graphene sheets throughout the observed region. Furthermore, Energy Dispersive X-ray Analysis (EDAX) provides the richness of carbon (C) in graphene as well as in the micro-oval structure. HRTEM gives an insight about the internal ultrastructure and arrangement of atoms in the sample which revealed the presence of multiple graphene sheets. The ring shape electron diffraction pattern and high resolution lattice fringes provide the arrangement of carbon atoms, with interlayer spacing (d) value 3.4 Å, well agreed with that of graphene. Furthermore, X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy support the presence of graphene. As a debut, we observe blue emission from PL spectroscopy with decay times 1.18 ns (42 %) and 5.41 ns (58 %).
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Materials Science · Cross-listed from cond-mat.mes-hall

Ultrafast Light-Induced Magnetoelectric Effect in van der Waals Magnetic Semiconductor Heterostructures

Wenyi Zhou, Ravi Kumar Bandapelli, Hari Paudyal et al. (+8 more)

Atomic-scale heterostructures of van der Waals (vdW) magnets and semiconductors provide a unique environment for exploring magnetic dynamics. In contrast to typical photothermal excitation of precessional magnetization dynamics by a pump laser pulse, we find that ultrafast optical excitation of a WS$_2$/CrGeTe$_3$ (CGT) bilayer produces an opposite sign of magnetic torque compared to an isolated CGT film. Experimental observations by time-resolved magneto-optic Kerr effect (TR-MOKE) and theoretical analysis by density functional theory (DFT) and Landau-Lifshitz-Gilbert (LLG) simulations support a mechanism in which charge transfer of photoexcited carriers across the interface alters the perpendicular magnetic anisotropy, which in turn generates a torque on the magnetic layer to trigger precessional magnetization dynamics. These results provide new avenues for ultrafast manipulation of magnetization in vdW heterostructures with type-II band alignments. Lastly, we show that optically-generated spin currents from WS$_2$ into CGT can also trigger precessional dynamics via angular momentum transfer.
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All authors Wenyi Zhou, Ravi Kumar Bandapelli, Hari Paudyal, Bangzheng Han, I-Hsuan Kao, Ziling Li, Yuqing Zhu, Durga Paudyal, Jyoti Katoch, Simranjeet Singh, Roland K. Kawakami

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

Room-temperature multistage metastability in a moiré superstructure

B. Q. Lv, Yifan Su, Alfred Zong et al. (+16 more)

Metastability is fundamental not only to phase ordering and transitions, but also to a broad range of modern technologies, from memory devices to metallic glasses. In condensed-matter physics, charge density waves (CDWs) offer versatile platforms for accessing metastable states due to their sensitivity to external stimuli. However, most metastable CDW states are stabilized only at low temperatures, limiting their practical utility. In this study, we report the observation of electrically driven, room-temperature, nonvolatile metastable states in the bulk form of EuTe$_4$, a recently discovered compound that hosts an innate moiré superlattice characterized by the stacking of incommensurate monolayer and bilayer CDWs. Systematic transport measurements reveal discrete resistivity plateaus and strong electric-field sensitivity, with a large number of metastable states readily induced across a wide temperature window within a giant hysteresis loop, making them well-suited for high-temperature, multi-bit memory applications. By integrating photoemission spectroscopy, diffraction, and in-situ transport measurements, we uncover that these metastable states do not stem from conventional mechanisms such as the emergence of new ordered phases or changes in incommensurate periodicity. Instead, they are characterized by a suppression of the original CDW amplitude and a reduction in correlation length, pointing to a unique electric-field-induced switching of out-of-plane CDW phases in the moiré superstructure. Our findings not only provide critical insights into metastable phenomena in moiré systems with stacked electronic orders but also establish EuTe$_4$ as a promising platform for developing room-temperature, multi-bit memory devices.
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All authors B. Q. Lv, Yifan Su, Alfred Zong, Karna Morey, Bryan T. Fichera, Qiaomei Liu, Dong Wu, Yongchang Ma, Dupeng Zhang, Faran Zhou, Makoto Hashimoto, Dong-Hui Lu, Donald A. Walko, Haidan Wen, Jiarui Li, Suchismita Sarker, Jacob P. C. Ruff, N. L. Wang, Nuh Gedik

Materials Science

Magnetic Polarons Enable Exceptional Magnetocaloric Response

Joshua Ancheta, Caeli Benyacko, Fanghao Zhang et al. (+2 more)

Magnetocaloric materials are typically limited by a trade-off between magnetic entropy and field responsiveness. Here we show that magnetic polarons provide an intermediate regime that mitigates this constraint and enables an exceptional magnetocaloric response. Using EuB$_6$ as a model system, we combine thermodynamic and magnetic measurements to demonstrate that nanoscale ferromagnetic clusters emerging near the Curie temperature strongly enhance the field-induced entropy collapse. These clusters possess large effective moments that respond efficiently to applied fields while retaining substantial entropy due to their small size and dynamic fluctuations. As a result, EuB$_6$ exhibits a giant cryogenic magnetocaloric response, with both large isothermal entropy change and adiabatic temperature change in the technologically important 10-40 K range. Our results identify magnetic polarons as an underexplored route for optimizing magnetocaloric performance and establish an intermediate magnetic length scale as a design principle for high-performance cryogenic cooling materials.
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All authors Joshua Ancheta, Caeli Benyacko, Fanghao Zhang, Stephen D. Wilson, Bolin Liao

Materials Science

Proximity Magnetism in Mn(Bi,Sb)2Te4-(Bi,Sb)2Te3/MnTe Natural Heterostructures

Owen A. Vail, Shu-Wei Wang, Yasen Hou et al. (+13 more)

Magnetic topological insulators and their heterostructures provide great opportunities in coupling band topology with nontrivial spin configuration for enhanced spintronic device performance as well as designing totally new magnetoelectric systems and functionalities. We find that Mn interdiffusion from MnTe when interfaced with (Bi,Sb)2Te3 stabilizes as self-organized Mn(Bi,Sb)2Te4 septuple lamellae amongst alternating (Bi,Sb)2Te3 quintuple layers, as observed using scanning transmission electron microscopy and depth-sensitive polarized neutron reflectometry. We further demonstrate a valuable combination of magnetic and topological orders in these naturally formed Mn(Bi,Sb)2Te4-(Bi,Sb)2Te3 heterostructures that are exchange coupled with MnTe. Magnetotransport experiments and quantum magnetism simulations reveal that, above its own Neel temperature TN of 20 K, Mn(Bi,Sb)2Te4 mediates the exchange field leading to an anomalous Hall effect at the (Bi,Sb)2Te3/MnTe interface, with an enhanced interfacial TN exceeding 200 K. This novel magnetic interface in turn allows a robust and deterministic spin-orbit torque switching without an external magnetic field at a low critical current density of 300 kA cm-2. The antiferromagnetically coupled architecture of Mn(Bi,Sb)2Te4-(Bi,Sb)2Te3/MnTe, featuring unique magnetic and topological proximity effects across a chalcogenide backbone, is rich in fundamental interface physics and holds potential for practical applications in spintronics.
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All authors Owen A. Vail, Shu-Wei Wang, Yasen Hou, Dinura Hettiarachchi, Jean-Felix Milette, Tim B. Eldred, Wenpei Gao, Wendy Sarney, Haile Ambaye, Jong Keum, Valeria Lauter, George J. de Coster, Matthew J. Gilbert, Don Heiman, Jagadeesh S. Moodera, Hang Chi

Monday 20 April

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

Stripping Symmetry: Electrochemical Oxidation to a Superconducting Polar Metal in Au2Pb0.914P2

Scott B. Lee, Stephanie R. Dulovic, Joseph W. Stiles et al. (+11 more)

Polar metals and noncentrosymmetric superconductors are exceptionally rare, yet their broken inversion symmetry can give rise to emergent electronic phenomena including mixed singlet-triplet superconducting pairing. As only a few such materials have been found among known compounds, accessing new examples requires synthetic strategies that go beyond conventional crystal growth. Here, we use electrochemical topotactic deintercalation to remove Pb from the centrosymmetric parent compound Au$_2$PbP$_2$, producing the polar metal Au$_2$Pb$_{0.914}$P$_2$. Unlike conventional chemical doping, this transformation actively drives structural symmetry-breaking: the partial removal of Pb triggers a cooperative electronic and geometric rearrangement, mediated by a second-order Jahn-Teller effect and stereochemically active lone pairs, that locks the product into a polar, noncentrosymmetric superspace group Ama2(01g)ss0. We solve the complete (3+1)D modulated structure by synchrotron single-crystal X-ray diffraction and confirm the polar assignment through nonlinear electronic transport. Below T$_c$ = 1.52 K, Au$_2$Pb$_{0.914}$P$_2$ becomes a type-II superconductor whose heat capacity and AC susceptibility both exhibit power-law behavior, suggestive of a gap structure governed by the broken inversion symmetry of the host lattice. This work establishes electrochemical oxidation as a rational route to metastable noncentrosymmetric superconductors through chemically directed symmetry-breaking.
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All authors Scott B. Lee, Stephanie R. Dulovic, Joseph W. Stiles, Xin Zhang, Fatmagül Katmer, Sudipta Chatterjee, Jaime Moya, Allana G. Iwanicki, Abby N. Neill, Chris Lygouras, Tieyan Chang, Tyrel M. McQueen, Yu-Sheng Chen, Leslie M. Schoop

Materials Science · Cross-listed from cs.AI

AI scientists produce results without reasoning scientifically

Martiño Ríos-García, Nawaf Alampara, Chandan Gupta et al. (+5 more)

Large language model (LLM)-based systems are increasingly deployed to conduct scientific research autonomously, yet whether their reasoning adheres to the epistemic norms that make scientific inquiry self-correcting is poorly understood. Here, we evaluate LLM-based scientific agents across eight domains, spanning workflow execution to hypothesis-driven inquiry, through more than 25,000 agent runs and two complementary lenses: (i) a systematic performance analysis that decomposes the contributions of the base model and the agent scaffold, and (ii) a behavioral analysis of the epistemological structure of agent reasoning. We observe that the base model is the primary determinant of both performance and behavior, accounting for 41.4% of explained variance versus 1.5% for the scaffold. Across all configurations, evidence is ignored in 68% of traces, refutation-driven belief revision occurs in 26%, and convergent multi-test evidence is rare. The same reasoning pattern appears whether the agent executes a computational workflow or conducts hypothesis-driven inquiry. They persist even when agents receive near-complete successful reasoning trajectories as context, and the resulting unreliability compounds across repeated trials in epistemically demanding domains. Thus, current LLM-based agents execute scientific workflows but do not exhibit the epistemic patterns that characterize scientific reasoning. Outcome-based evaluation cannot detect these failures, and scaffold engineering alone cannot repair them. Until reasoning itself becomes a training target, the scientific knowledge produced by such agents cannot be justified by the process that generated it.
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All authors Martiño Ríos-García, Nawaf Alampara, Chandan Gupta, Indrajeet Mandal, Sajid Mannan, Ali Asghar Aghajani, N. M. Anoop Krishnan, Kevin Maik Jablonka

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

Dynamical magnetism in the disordered cubic lattice material $\gamma$-${\rm Ba}_{3}{\rm CoNb}_{2}{\rm O}_{9}$

Fanjun Xu, Ralf Feyerherm, Cecilie Glittum et al. (+12 more)

$\gamma$-${\rm Ba}_{3}{\rm CoNb}_{2}{\rm O}_{9}$ realizes a disordered simple-cubic spin-$1/2$ lattice in which Co$^{2+}$ ions randomly occupy one third of the sites, placing the system close to the site-percolation threshold for magnetic order. Specific-heat, susceptibility, neutron spin-echo, and muon spin-rotation measurements reveal a broad thermodynamic crossover, short-range magnetic correlations, and persistent fast spin dynamics down to at least 0.1~K, with no evidence for static order or conventional spin-glass freezing. Monte Carlo simulations yield a broad distribution of orphan spins, finite clusters, and an infinite network. The calculated orphan-spin fraction ($\approx 8.8\%$) agrees well with the weakly correlated spin fraction inferred from magnetization ($\approx 8.2\%$). Exact diagonalization of a diluted $S = 1/2$ Heisenberg model captures the broad magnetic specific-heat anomaly and supports the coexistence of weakly and strongly correlated spin environments. These results support a picture in which spin-$1/2$ quantum fluctuations, together with dilution and proximity to the percolation threshold, can support a disorder-driven dynamical state with short-range correlations in three dimensions, distinct from both classical spin glasses and geometrically frustrated quantum spin liquids.
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All authors Fanjun Xu, Ralf Feyerherm, Cecilie Glittum, Thomas J. Hicken, Hubertus Luetkens, Jonas A. Krieger, Cintli Aguilar-Maldonado, Sven Luther, Lucy K. Saunders, Clemens Ritter, Peter Fouquet, Margarita Russina, Karel Prokes, A.T.M. Nazmul Islam, Bella Lake

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

Proximitized Topological Insulator Charge Island Fabricated via In Situ Multi-Angle Stencil Lithography

Benedikt Frohn, Tobias Schmitt, Vanessa Serrano et al. (+7 more)

Hybrid superconductor-topological insulator (TI) nanostructures constitute a promising material platform for exploring proximity-induced superconductivity in systems with topologically protected surface states. A key obstacle has been the realization of clean and well-controlled superconductor-TI interfaces, as TI surfaces rapidly degrade under ambient conditions. Here, we introduce a fully in situ, multi-angle stencil lithography technique that enables the fabrication of proximitized charge islands in TIs. The approach combines selective area growth of (Bi,Sb)$_2$Te$_3$ nanoribbons with angle-controlled deposition of diffusion barriers, superconducting Al, and ultrathin oxide tunnel barriers, allowing scalable fabrication of hybrid nanostructures without post-growth processing. Low-temperature transport measurements reveal robust Coulomb blockade and a pronounced suppression of low-energy conductance, which vanishes with a magnetic field, consistent with proximity-induced superconductivity in the island. These results establish a versatile nanofabrication platform that enables access to previously unexplored TI-based hybrid quantum devices and opens new routes for investigating superconductivity in topological nanostructures.
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All authors Benedikt Frohn, Tobias Schmitt, Vanessa Serrano, Anne Schmidt, Michael Schleenvoigt, Albert Hertel, Benjamin Bennemann, Abdur Rehman Jalil, Detlev Grützmacher, Peter Schüffelgen

Materials Science

General Conditions for Axis Dependent Conduction Polarity

Poulomi Chakraborty, Brian Skinner and Penghao Zhu

Axis-Dependent Conduction Polarity (ADCP) refers to the phenomenon in which electrical transport within a single material is p-type along one crystallographic direction and n-type along the perpendicular direction. This behavior enables a variety of thermoelectric applications that do not require a heterojunction between two different materials. In this work, we investigate ADCP theoretically and derive a set of generic and quantitative criteria for identifying and predicting materials that exhibit ADCP. Specifically, by analyzing the thermopower for generic metals, semimetals, and semiconductors, we obtain transparent inequalities that are both necessary and sufficient for the emergence of ADCP. Moreover, we review known ADCP materials and verify that their band-structure characteristics and relaxation parameters are consistent with the inequalities derived here.
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Materials Science

Thermo-mechanically coupled phase-field fracture model considering elastocaloric effect of shape memory alloy

Shen Sun, Wei Tang, Weiwei He et al. (+2 more)

Modelling fracture behavior of the shape memory alloy (SMA) that interacts with martensitic transformation and the associated elastocaloric effect (eCE) still remains challenging. Herein, a thermo-mechanically coupled phase-filed fracture model considering elastocaloric effect of SMA is proposed to simulate the cracking process coupled with the non-isothermal martensitic transformation and the associated eCE. In the phase-field model, both the thermal strain induced by eCE and the eigen strain induced by the phase transition are considered. An empirical degradation function is adopted to describe the thermal conductivity decreasing with the fracture order parameter. The model is validated with the finite element method and tensile fracture properties of Mn-Cu SMA are simulated. It is found that the martensite variant nucleates at the stress concentration where the crack initiates, and commonly spreads with an angle of 45 degree. The thermal expansion strain caused by the eCE could strengthen the critical load capacity. A large kinetic parameter for phase transition and the large orientation angle could enhance the strength and temperature change of eCE while the deformation capacity is reduced. The phase-field model demonstrates its ability in the thermal-mechanically coupled toughening of SMA. It also provides a possible fracture-resistance strategy by the utilization of eCE for elastocaloric devices.
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All authors Shen Sun, Wei Tang, Weiwei He, Igor Polozov, Min Yi

Materials Science

Moire Control of Alterelectric Quadrupolar Order

Alejandro Lopez-Bezanilla

Alterelectricity is a compensated ferroic state in which quadrupolar electronic order reshapes low-energy electronic structure without producing a net polarization. Here we show that a moiré superlattice can turn such order into a controllable phase. Within a Bloch-periodic two-orbital theory, the slowly varying interlayer registry is coarse-grained into an effective moiré field acting on a self-consistent two-component alterelectric quadrupole. The resulting phase develops above a strongly filling-dependent instability threshold and crosses over from a weakly selected regime into a robust axial-dominated ground state, while the diagonal-dominated branch remains only a weak competitor. A registry-phase sweep supplies an explicit continuous path through internal quadrupole space, demonstrating that the moiré superlattice does more than stabilize alterelectricity: it steers its internal orientation. This orientational selection is encoded directly in the redistribution of low-energy spectral weight across the moiré Brillouin zone. These results identify moiré superlattices as a generic route to controllable alterelectric order and to programmable anisotropic electronic functionality.
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Materials Science

Plasmonic Photocatalysis Enables Selective Oxidative Coupling of Methane with Nitrous Oxide under Ambient Conditions

Serin Lee, Lin Yuan, Elijah Begin et al. (+8 more)

Methane (CH4) and nitrous oxide (N2O) are potent greenhouse gases that represent substantial chemical energy. Conversion of these abundant waste gases to high-value chemicals typically requires high temperatures up to 1000 C, producing substantial CO2 emissions and limited selectivity toward desirable multi-carbon products. Here we demonstrate a plasmonic photocatalyst that enables CH4 and N2O conversion under ambient conditions to form C2 and C3 hydrocarbons. By systematically tuning AuPd alloys on TiO2, we identify an optimal composition (AuPd0.05) where Au enhances light harvesting and Pd enables selective C-H activation and C-C coupling. Under visible-light illumination, this catalyst produces C2H4, C2H6, C3H6, and C3H8 with ~80% selectivity while suppressing CO2 formation. In-situ spectroscopy and hot-carrier calculations show that plasmon-generated carriers redistribute interfacial hydroxyl intermediates, shifting the hydrophilic center to suppress overoxidation. Ab-initio calculations further reveal the reduction in C-C coupling barriers from 2.7 eV to 0.7 eV under illumination. Our work illustrates how engineering interfacial electronic and adsorbate dynamics enables selective multicarbon formation.
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All authors Serin Lee, Lin Yuan, Elijah Begin, Dali Yang, Cedric Lim, Yirui Arlene Zhang, Lu Ma, Colin Ophus, Yi Cui, Junwei Lucas Bao, Jennifer A. Dionne

Materials Science

Direct observation of quadruple spin-texture locking in a 2D d-wave altermagnet

Dan Mu, Bei Jiang, Qingchen Duan et al. (+14 more)

Altermagnets combine vanishing net magnetization with nonrelativistic, momentum-dependent spin splitting, offering a new paradigm for spintronics. Spin-crystal symmetry coupling, namely spin-lattice locking, is the defining mechanism of altermagnetism, enforcing opposite spin sublattices in real space and spin-momentum-locked electronic structure in reciprocal space. Direct atomic-scale visualization of spin-lattice locking therefore constitutes a decisive benchmark of the altermagnetic state, yet such evidence has remained elusive despite extensive efforts. Here we show that the electronic states in RbV2Se2O exhibit a d-wave-like spin texture at the sublattice level, providing the first atomic-scale evidence of spin-lattice locking with a predominantly c-axis spin orientation. By employing an in-situ, field-switchable spin-polarized Cr tip, we realize spin-contrast mapping of quasiparticle interference at identical energies, overcoming a long-standing experimental barrier in altermagnets. The resulting interference patterns exhibit pronounced spin-dependent modulations, establishing spin scattering locking and spin momentum locking as the real and reciprocal space manifestations. Unexpectedly, we uncover that the spin-selective scattering response is organized by a long-period stripe modulation, giving rise to a previously unidentified form of spin-texture locking, spin-stripe locking. We attribute this behavior to the emergence of a spin-density-wave moiré pattern. Together, these results establish a unified picture of quadruple spin-texture locking phenomena in a d-wave altermagnet, and position altermagnets as a versatile platform for exploring many-body interactions among intertwined degrees of freedom, including spin, lattice, momentum, moiré potential and valley.
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All authors Dan Mu, Bei Jiang, Qingchen Duan, Zulin Xu, Xingkai Cheng, Yusen Xiao, Xinru Han, Xinyu Liang, Zhaokun Luo, Ryan L. Kong, Qiheng Wang, Junwei Liu, Jianxin Zhong, Ruidan Zhong, Qiangqiang Gu, Baiqing Lv, Hong Ding

Materials Science

Multipolar Piezoelectricity and Anisotropic Surface Transport in Alterelectrics

Amber Visser, Viktor Könye, Oleg Janson et al. (+3 more)

Altermagnets are an emergent class of materials combining features of ferro- and antiferro-magnetic materials. They have spin-separated bands normally associated with ferromagnets, but a vanishing net magnetization. Moreover the symmetries giving rise to $d$-wave altermagnetism can provide them with a particular anisotropic, quadrupolar (i.e. with equal and opposite values when strained in perpendicular directions) piezomagnetism. Observing that the same symmetries provide a natural place to look for hyberbolic wave dispersion, this raises the question which properties are intrinsically linked to magnetism and which are determined by the symmetry. Here, we disentangle these concepts by introducing an alternative to altermagnets, based on electric polarization. These alterelectrics display quadrupolar piezoelectricity and a hyperbolic dispersion, which we demonstrate conceptually within a simplified model as well as a first-principles material realization. We furthermore establish that a counterpart of the spin-separated bands is formed by surface modes which allow for surface dependent anisotropic electronic transport analogous to the spintronic applications proposed for altermagnets.
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All authors Amber Visser, Viktor Könye, Oleg Janson, Jeroen van den Brink, Corentin Coulais, Jasper van Wezel