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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Tuesday 9 December

Materials Science

Benchmarking First-Principles Approaches for Extracting Magnetic Exchange Interactions

Nafise Rezaei, Artem R. Oganov, Ali Ghojavand et al. (+2 more)

Magnetic exchange interactions govern the macroscopic magnetic behavior of solids and underpin both fundamental spin phenomena and emerging technologies. The accurate and efficient determination of these interactions is therefore critical for predictive modeling of magnetic materials. Here we present a systematic first-principles comparison of three widely used approaches-the Least-Squares Total Energy (LSTE), the Four-State Total Energy (FSTE), and the Green's function-based Liechtenstein et al. (LKAG) methods-applied to thirteen antiferromagnetic compounds. We introduce an framework for identifying the minimal supercells required for an accurate exchange parameter extraction in the FSTE method, significantly reducing computational cost while preserving precision. Our results show that LSTE and FSTE yield nearly identical exchange parameters, whereas the LKAG method reproduces the dominant exchange interactions but exhibits quantitative deviations. A detailed analysis of computational efficiency versus accuracy reveals that the LSTE scheme offers the most favorable balance, establishing a general, reproducible, and scalable workflow for Heisenberg mapping, while the FSTE approach remains the most straightforward for extracting specific exchange interactions.
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All authors Nafise Rezaei, Artem R. Oganov, Ali Ghojavand, Milorad V. Milošević, Mojtaba Alaei

Materials Science

Synthesis, Growth Mechanism, and Photocatalytic Properties of Metallic-Bi/Bi13S18Br2 Nano-Bell Heterostructures

Anna Cabona, Stefano Toso, Andrea Griesi et al. (+8 more)

We report the synthesis of bell-shaped Bi/Bi13S18Br2 metal/semiconductor heterostructures as a photocatalyst based on non-toxic and Earth-abundant elements. Their unique morphology arises from a multi-step growth process, involving 1) the nucleation of Bi13S18Br2 nanorods, 2) the reduction of a metallic-Bi domain on their surface induced by N,N-didodecylmethylamine, and 3) the heterostructure accretion by a localized reaction at the Bi/Bi13S18Br2 interface promoted by Ostwald ripening. These heterostructures display remarkable stability in polar solvents, remaining almost unaffected by prolonged exposure to isopropanol and water, and exhibit high photocatalytic efficiency for the degradation of organic dyes (i.e., Rhodamine-B and Methylene Blue) under visible-light irradiation, with good recyclability. Additionally, preliminary tests demonstrate CO2 reduction capabilities, which make them promising for both the photocatalytic degradation of pollutants and photo-electro CO2 conversion. The straightforward synthesis process and the use of non-toxic and earth-abundant elements offers significant potential for sustainable energy conversion technologies.
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All authors Anna Cabona, Stefano Toso, Andrea Griesi, Martina Rizzo, Michele Ferri, Pascal Rusch, Giorgio Divitini, Julia Perez-Prieto, Raquel E. Galian, Ilka Kriegel, Liberato Manna

Materials Science

Modeling the Effects of Slip, Twinning, and Notch on the Deformation of Single-Crystal Austenitic Manganese Steel

Saketh Virupakshi, Xinzhu Zheng, Karol Frydrych et al. (+3 more)

The objective of this work is to deconvolute the interaction of slip, twinning, and notch on the deformation response of an austenitic manganese (Hadfield) steel using detailed finite element simulations. The simulations employ a rate-dependent crystal plasticity constitutive model that incorporates both slip and twinning deformation mechanisms. The model accounts for the spatially non-uniform appearance of new twin-related orientations, hardening due to slip–twin interactions, and modified properties of the twinned crystal. Limited experiments on single-crystal dog-bone and single-edge notch specimens, with two crystal orientations, are also conducted to aid the simulation. Several features of the experimental observations are accurately captured in the simulations. For example, simulations accurately capture distinct stress–strain responses associated with different crystallographic orientations, including variations in initial hardening behavior followed by either decreasing or increasing hardening depending on the dominant deformation mechanisms. The simulation also captures the observed orientation-dependent asymmetric deformation of the notch in single-edge notch specimens. Additionally, by selectively activating deformation mechanisms, the role of twinning is isolated and its influence on both global and local response is clearly demonstrated. These results provide a mechanistic understanding of how deformation mode interactions and local geometry (i.e., notch) influence the response of these materials.
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All authors Saketh Virupakshi, Xinzhu Zheng, Karol Frydrych, Ibrahim Karaman, Ankit Srivastava, Katarzyna Kowalczyk-Gajewska

Materials Science

The unexpected dewetting during growth of silicene flakes with dendritic pyramids

Kejian Wang, Mathieu Abel, Filippo Fabbri et al. (+6 more)

Silicene growth on graphene has emerged as a novel method for fabricating silicon-based van der Waals heterostructures. However, the silicene flakes produced in this manner are the result of an exotic growth mode characterized by metastable nanostructures with varying degrees of deviation from equilibrium, with large two-dimensional flakes surrounded by a rim that coexist with small 3D islands, and, at large deposits, thick dendritic pyramids separated by a denuded zone. In order to rationalize and control this growth, a model is derived that revisits the dewetting thermodynamics and considers generally ignored adsorption and step-edge energies. The model is investigated using kinetic Monte-Carlo simulations and mean-field rate equations, and implemented by close inspection of microscopy images. This model perfectly reproduces the experimental outcomes, unveiling an anomalous growth mode, and provides guidelines on experimental conditions for high-quality silicene growth.
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All authors Kejian Wang, Mathieu Abel, Filippo Fabbri, Mathieu Koudia, Adrien Michon, Adam Hassan Denawi, Holger Vach, Isabelle Berbezier, Jean-Noël Aqua

Materials Science

Chiral-phonon generation of orbital currents in light transition metals

Marc Rovirola, Júlia Òdena, Anna Castellví et al. (+10 more)

Orbital angular momentum offers a new channel for information transport in a vast set of materials. Its coherent generation and detection remain, however, largely unexplored. Here, we demonstrate that chiral surface acoustic waves (SAWs) generate sizable orbital currents in light-metal/ferromagnet bilayers through both the acoustic orbital Hall effect and acoustic orbital pumping. Using symmetry analysis of SAW-driven voltages, we disentangle vorticity-sensitive orbital currents arising from lattice rotation in the non-magnetic layer from angular-momentum pumping from the ferromagnet. Strong signals are observed only in nickel/chromium and nickel/titanium, while nickel/aluminum and all cobalt-based bilayers show negligible responses, revealing the critical roles of orbital Hall conductivity, phonon-orbital coupling, and interfacial orbital transparency. Comparison with spin-torque ferromagnetic resonance and second-harmonic measurements – where electrically driven orbital angular momentum are weaker – demonstrates that phonon excitation generates orbital currents more efficiently. These results establish chiral SAWs as an effective route for orbitronic functionality and open pathways toward phonon-controlled orbital magnetism.
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All authors Marc Rovirola, Júlia Òdena, Anna Castellví, Quim Badosa, Blai Casals, Adrián Gudín, Haripriya Madathil, Fernando Ajejas, Paolo Perna, Alberto Hernández-Mínguez, Joan Manel Hernández, Saül Vélez, Ferran Macià

Materials Science · Cross-listed from physics.optics

Dielectric permittivity tensor dynamics of in-plane hyperbolic van der Waals MoOCl2 and emergent chiral photonic applications

Artsruni Margaryan, Maksim Sargsyan, Meri Hayrapetyan et al. (+3 more)

Van der Waals (vdW) crystals offer unique opportunities for modern nanophotonic applications owing to their intrinsic anisotropic nature. While most of them exhibit uniaxial anisotropy arising from weak out-of-plane vdW interaction, some of their representative families also exhibit an in-plane biaxial anisotropy. Among the latter, outstand vdW oxochlorides with in-plane axes of a different physical character (metallic or dielectric). Here, we present an accurate dynamics of dielectric permittivity tensor components of vdW MoOCl2 in the ultraviolet (UV) to visible (Vis) spectral region partly covering near-infrared (NIR). Addressing its enormously anisotropic optical constants, we focus on another hyperbolicity window of vdW MoOCl2 emerging in the UV spectral region that may potentially unlock rich light-matter interaction effects. Furthermore, we propose an approach towards designing nanoscale handedness preserved Vis light circular polarizers based on twisted helical vdW MoOCl2 heterostructures. Our findings display that vdW MoOCl2 provides a highly promising platform not only for hyperbolic, but also for chiral nanophotonic applications.
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All authors Artsruni Margaryan, Maksim Sargsyan, Meri Hayrapetyan, David Karakhanyan, Kostya S. Novoselov, Davit A. Ghazaryan

Materials Science

Disorder-mediated linear and nonlinear magnetotransport in the charge-density-wave material ${\rm Ta_2NiSe_7 }$

Xiaodong Sun, Jiabin Qiao, Yuanzhe Li et al. (+13 more)

We report disorder-mediated first-order linear and higher-order nonlinear (magneto-)transport of Ta$_2$NiSe$_7$ (TNS) in the charge-density-wave (CDW) regime. CDW transition temperature ($T_{CDW}$) and carrier density are proportional and inversely proportional to residual resistance ratio of samples, respectively. Such relation helps to understand the unique CDW order therein. High-$T_{CDW}$ TNS exhibits negative first-harmonic magnetoresistance (MR$^{1\omega}$) under a magnetic field ($B$) parallel to the direction of alternating current ($I^{\omega}$), which may arise from the anomalous velocity induced by the Berry curvature of three-dimensional topological bands near the Fermi level. As $T_{CDW}$ drops, a positive-to-negative MR$^{1\omega}$ transition is observed with decreasing perpendicular $B$, which is likely due to the contribution of Zeeman effect on current pathways in the disordered system. Moreover, interestingly, the second-harmonic nonlinear signals are suppressed, while the third-harmonic signals are significant and sensitive to both $B$ and $T_{CDW}$. Such observations, together with scaling analysis, suggest the quantum geometry quadrupole at play and the modulation of disorder on third-order nonlinearity. Our results pave an avenue for tailoring distinct-order magnetoresistive phases in disordered topological materials.
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All authors Xiaodong Sun, Jiabin Qiao, Yuanzhe Li, Wanli He, Jiali Chen, Jinjin Liu, Yuxiang Chen, Yuchen Ma, Meiling Jin, Jianlin Luo, Jie Chen, Wei Wu, Zhiwei Wang, Wei Jiang, Xiang Li, Yugui Yao

Materials Science

Structural and Thermal Stability of B4C/Ru Multilayers with Carbon Barrier Layers

A.V. Bugaev, S.S. Sakhonenkov, A.U. Gaisin et al. (+3 more)

The chemical interaction between Mo and Ru layers in multilayer structures depending on the thickness ratio ($\Gamma$) was carried out using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and X-ray reflectometry (XRR). The results showed significant interaction of materials inside multilayer structures with the formation of ruthenium borides, with an increase in the B4C layer thickness (a decrease in the $\Gamma$ parameter) leading to the formation of ruthenium borides of different stoichiometry. The introduction of a carbon barrier layer at the Ru-on-B4C interface resulted in significant suppression of ruthenium boride formation. The thermal stability of the B4C/Ru system was also studied upon annealing at 400$^{\circ}$C for 1 hour before and after the introduction of the carbon barrier layer. It was shown that the introduction of a carbon barrier layer at the Ru-on-B4C interface increases the thermal stability of the system, which makes this system more suitable for use in optical systems exposed to long-term radiation. The obtained results are important for the development of highly efficient multilayer mirrors used in EUV lithography and X-ray optics.
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All authors A.V. Bugaev, S.S. Sakhonenkov, A.U. Gaisin, R.A. Shaposhnikov, V.N. Polkovnikov, E.O. Filatovaa

Materials Science

Halogen Chains with One-Dimensional Semi-Metallic Electronic Structure and Peierls Physics in Polymorphs of Na4X5 (X = I, Br, Cl) Compounds

Yuqing Yin, Nityasagar Jena, Florian Knoop et al. (+16 more)

Since the pioneering works of Peierls, one-dimensional materials have attracted great attention. Still, the synthesis of truly monoatomic chains remains elusive. In this study, we explore a novel path of experimental synthesis of monoatomic one-dimensional chains by their chemical stabilization in ionic compounds. We demonstrate that in synthesized at high pressure sodium halides Na4X5 (X = I, Br, Cl) with hP18 Ga4Ti5-type structures, transfer of valence electrons from cations to anions leads to the formation of halogen chains connected with other atoms only by ionic interaction and having one-dimensional electronic structure. The Peierls physics in the systems is confirmed by theoretical calculations, newly synthesized incommensurately modulated i-hP18-Na4X5 (X = I, Br, Cl) compounds, as well as by the discovered hP36 phases of Na4Cl5 and Na4Br5.
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All authors Yuqing Yin, Nityasagar Jena, Florian Knoop, Gaston Garbarino, Ferenc Tasnádi, Florian Trybel, Sergei I. Simak, Mikhail I. Katsnelson, Alena Aslandukova, Andrey Aslandukov, Xiang Li, Anaëlle Antunes, Fariia Iasmin Akbar, Konstantin Glazyrin, Haixing Fang, James A. D. Ball, Natalia Dubrovinskaia, Leonid Dubrovinsky, Igor A. Abrikosov

Materials Science

Ultrafast light-induced formation of a metastable hidden state in bismuth vanadate

Viktoria F. Kunzelmann, Verena Streibel, Philip Schwinghammer et al. (+24 more)

Bismuth vanadate (BiVO$_4$) is a key photocatalyst for solar fuel applications, yet fundamental questions remain regarding the nature of photogenerated polaronic states and the lattice dynamics that govern its light-to-chemical pathways. Here, we use femtosecond optical pump-X-ray probe measurements to track the photoinduced electronic and structural dynamics in BiVO$_4$ across multiple length and time scales. Transient X-ray absorption spectroscopy captures sub-picosecond electron localization within VO$_4$ tetrahedra, consistent with small polaron formation, whereas time-resolved X-ray diffraction reveals a slower, multi-picosecond lattice reorganization into a hidden photoexcited state that is structurally distinct from both the monoclinic ground state and the high-temperature tetragonal phase. Supported by density functional theory, we show that hole-lattice interactions dynamically reduce the ground state monoclinic distortion, stabilizing the hidden state. Our results demonstrate that electron- and hole-lattice coupling jointly shape the excited state landscape, with implications for carrier transport, interfacial energetics, and light-to-chemical energy conversion pathways.
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All authors Viktoria F. Kunzelmann, Verena Streibel, Philip Schwinghammer, Philipp Kollenz, Burak Guzelturk, Franziska S. Hegner, Lissa Eyre, Frederico P. Delgado, Tsedenia A. Zewdie, Markus W. Heindl, Danyellen D. Monteiro Galindo, Daniel Sandner, Guanda Zhou, Elise Sirotti, Stanislav Bodnar, Yifeng Jiang, Yohei Uemura, Tobias Eklund, Frederico Lima, Xinchao Huang, Doriana Vinci, Fernando Ardana Lamas, Peter Zalden, Hristo Iglev, David A. Egger, Felix Deschler, Ian D. Sharp

Materials Science

A Transcorrelated Wave-Function Framework for Solids: An Application to Bulk and Defected Silicon

Kristoffer Simula, Johannes Hauskrecht, Evelin Martine Corvid Christlmaier et al. (+4 more)

Accurate wave-function descriptions of pristine and defected solids remain challenging due to the simultaneous presence of finite-size, basis-set, and correlation errors. While embedding techniques alleviate finite-size effects and correlated wave-function approaches systematically improve correlation, basis-set incompleteness continues to limit practical accuracy. Here we present a study of transcorrelated (TC) many-body wave-function methods on properties of solid state systems. We augment the existing xTC theory to periodic systems, and establish an unified transcorrelated embedding framework that integrates periodic TC theory with fragment-based correlated solvers. Using silicon as a test case, we validate the method against coupled-cluster, FCIQMC, and diffusion Monte Carlo benchmarks for bulk. Then we apply TC embedding to calculation of formation energies of two silicon self-interstitials. The TC Hamiltonian yields rapid basis convergence and quantitatively reliable defect formation energies at the triple-$\zeta$ level, substantially reducing the basis-set bottleneck for wave-function treatments of crystalline defects.
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All authors Kristoffer Simula, Johannes Hauskrecht, Evelin Martine Corvid Christlmaier, Pablo Lopez-Rios, Daniel Kats, Denis Usvyat, Ali Alavi

Materials Science

Coalescence of multiple topological orders in quasi-one-dimensional bismuth halide chains

Jingyuan Zhong, Ming Yang, Wenxuan Zhao et al. (+14 more)

Topology is being widely adopted to understand and to categorize quantum matter in modern physics. The nexus of topology orders, which engenders distinct quantum phases with benefits to both fundamental research and practical applications for future quantum devices, can be driven by topological phase transition through modulating intrinsic or extrinsic ordering parameters. The conjoined topology, however, is still elusive in experiments due to the lack of suitable material platforms. Here we use scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and theoretical calculations to investigate the doping-driven band structure evolution of a quasi-one-dimensional material system, bismuth halide, which contains rare multiple band inversions in two time-reversal-invariant momenta. According to the unique bulk-boundary correspondence in topological matter, we unveil a composite topological phase, the coexistence of a strong topological phase and a high-order topological phase, evoked by the band inversion associated with topological phase transition in this system. Moreover, we reveal multiple-stage topological phase transitions by varying the halide element ratio: from high-order topology to weak topology, the unusual dual topology, and trivial/weak topology subsequently. Our results not only realize an ideal material platform with composite topology, but also provide an insightful pathway to establish abundant topological phases in the framework of band inversion theory.
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All authors Jingyuan Zhong, Ming Yang, Wenxuan Zhao, Kaiyi Zhai, Xuan Zhen, Lifu Zhang, Dan Mu, Yundan Liu, Zhijian Shi, Ningyan Cheng, Wei Zhou, Jianfeng Wang, Weichang Hao, Zhenpeng Hu, Jincheng Zhuang, Jinhu Lü, Yi Du

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

Field manipulation of Weyl modes in an ideal Dirac semimetal

Jingyuan Zhong, Jianfeng Wang, Ming Yang et al. (+9 more)

The emergent Weyl modes with the broken time-reversal symmetry or inversion symmetry provide large Berry curvature and chirality to carriers, offering the realistic platforms to explore topology of electrons in three-dimensional systems. However, the reversal transition between different types of Weyl modes in a single material, which is of particular interest in the fundamental research in Weyl physics and potential application in spintronics, is scarcely achieved due to restriction of inborn symmetry in crystals. Here, by tuning the direction and strength of magnetic field in an ideal Dirac semimetal, Bi4(Br0.27I0.73)4, we report the realization of multiple Weyl modes, including gapped Weyl mode, Weyl nodal ring, and coupled Weyl mode by the magnetoresistivity measurements and electronic structure calculations. Specifically, under a magnetic field with broken mirror symmetry, anomalous Hall effect with step feature results from the large Berry curvature for the gapped Weyl mode. A prominent negative magnetoresistivity is observed at low magnetic field with preserved mirror symmetry and disappears at high magnetic field, which is correlated to the chiral anomaly and its annihilation of Weyl nodal ring, respectively. Our findings reveal distinct Weyl modes under the intertwined crystal symmetry and time-reversal breaking, laying the foundation of manipulating multiple Weyl modes in chiral spintronic network.
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All authors Jingyuan Zhong, Jianfeng Wang, Ming Yang, Jie Liu, Zhizhen Ren, Anping Huang, Zhixiang Shi, Zengwei Zhu, Yan Shi, Weichang Hao, Jincheng Zhuang, Yi Du

Materials Science

Enhancing Hole Mobility in Monolayer $WSe_{2}$ p-FETs via Process-Induced Compression

He Lin Zhao, Sheikh Mohd Ta-Seen Afrid, Dongyoung Yoon et al. (+7 more)

Understanding the interactions between strain, interfacial mechanics, and electrical performance is critical for designing beyond silicon electronics based on hetero-integrated 2D materials. Through combined experiment and simulation, we demonstrated and analyzed the enhancement of hole mobility in p-type monolayer $WSe_{2}$ field effect transistors (FETs) under biaxial compression. We tracked FET performance versus strain by incrementing compressive strain to $WSe_{2}$ channels via sequential AlOx deposition and performing intermediate photoluminescence and transport measurements. The hole mobility factor increased at a rate of 340 $\pm$ 95 %/%$\epsilon$, and the on-current factor increased at a rate of 460 $\pm$ 340 %/%$\epsilon$. Simulation revealed that the enhancement under compression arises primarily from a reduction in inter-valley scattering between the $\Gamma$–K valence bands, and the rate is robust against variations in carrier density, impurity density, or dielectric environment. These findings show that compressive strain is a powerful technique for enhancing performance in 2D p-FETs and that it is multiplicative with defect and doping engineering.
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All authors He Lin Zhao, Sheikh Mohd Ta-Seen Afrid, Dongyoung Yoon, Zachary Martin, Zakaria Islam, Sihan Chen, Yue Zhang, Pinshane Y. Huang, Shaloo Rakheja, Arend M. van der Zande

Monday 8 December

Materials Science · Cross-listed from eess.IV

Missing Wedge Inpainting and Joint Alignment in Electron Tomography through Implicit Neural Representations

Cedric Lim, Corneel Casert, Arthur R. C. McCray et al. (+4 more)

Electron tomography is a powerful tool for understanding the morphology of materials in three dimensions, but conventional reconstruction algorithms typically suffer from missing-wedge artifacts and data misalignment imposed by experimental constraints. Recently proposed supervised machine-learning-enabled reconstruction methods to address these challenges rely on training data and are therefore difficult to generalize across materials systems. We propose a fully self-supervised implicit neural representation (INR) approach using a neural network as a regularizer. Our approach enables fast inline alignment through pose optimization, missing wedge inpainting, and denoising of low dose datasets via model regularization using only a single dataset. We apply our method to simulated and experimental data and show that it produces high-quality tomograms from diverse and information limited datasets. Our results show that INR-based self-supervised reconstructions offer high fidelity reconstructions with minimal user input and preprocessing, and can be readily applied to a wide variety of materials samples and experimental parameters.
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All authors Cedric Lim, Corneel Casert, Arthur R. C. McCray, Serin Lee, Andrew Barnum, Jennifer Dionne, Colin Ophus

Materials Science

Moire-Engineered Ferroelectric Transistors for Nearly Trap-free, Low-Power and Non-Volatile 2D Electronics

Arup Singha, Shaili Sett, Kenji Watanabe et al. (+3 more)

Long-range moire patterns in twisted WSe2 enable a built-in, moire-length-scale ferroelectric polarization that can be directly harnessed in electronic devices. Such a built-in ferroic landscape offers a compelling means to enable ultralow-voltage and non-volatile electronic functionality in two-dimensional materials; however, achieving stable polarization control without charge trapping has remained a persistent challenge. Here, we demonstrate a moire-engineered ferroelectric field-effect transistor (FeFET) utilizing twisted WSe2 bilayers that leverages atomically clean van der Waals interfaces to achieve efficient polarization-channel coupling and trap-suppressed, ultralow-voltage operation (subthreshold swing of 64 mV per decade). The device exhibits a stable non-volatile memory window of 0.10 V and high mobility, exceeding the performance of previously reported two-dimensional FeFET and matching that of advanced silicon-based devices. In addition, capacitance-voltage spectroscopy, corroborated by self-consistent Landau-Ginzburg-Devonshire modeling, indicates ultrafast ferroelectric switching (~0.5 microseconds). These results establish moire-engineered ferroelectricity as a practical and scalable route toward ultraclean, low-power, and non-volatile 2D electronics, bridging atomistic lattice engineering with functional device architectures for next-generation memory and logic technologies.
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All authors Arup Singha, Shaili Sett, Kenji Watanabe, Takashi Taniguchi, Arindam Ghosh, Rahul Debnath

Materials Science

Bayesian Co-Navigation of a Computational Physical Model and AFM Experiment to Autonomously Survey a Combinatorial Materials Library

Boris N. Slautin, Kamyar Barakati, Yu Liu et al. (+3 more)

Building autonomous experiment workflows requires transcending beyond the data-driven surrogate models to incorporate and dynamically refine physical theory during exploration. Here we demonstrate the first fully automated experimental realization of Bayesian co-navigation - a framework in which an autonomous agent simultaneously runs a physical experiment and a computationally expensive physical model. Using an automated AFM platform coupled to a kinetic Monte Carlo (kMC) model of thin-film growth, the system infers a set of effective bond energies for the (CrTaWV)x-Mo(1-x) pseudo-binary combinatorial library, progressively adjusting the kMC parameters to decrease the epistemic disparity between simulation and experiment. This real-time theoretical refinement enables the kMC model to capture the behavior of the specific materials system and reveals the mechanistic role of hetero-bonding in governing surface diffusion. Together, these results establish co-navigation as a general strategy for tightly integrating physical models with autonomous experimental platforms to produce interpretable and continually self-correcting theoretical modelling of complex materials systems.
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All authors Boris N. Slautin, Kamyar Barakati, Yu Liu, Reece Emery, Philip Rack, Sergei V. Kalinin

Materials Science

Predicting interstitial elements in Refractory Complex Concentrated Alloys

Aomin Huang, Siya Zhu, Calvin Belcher et al. (+4 more)

Refractory complex concentrated alloys, composed of multiple principal refractory elements, are promising candidates for high-temperature structural applications due to their exceptional thermal stability and high melting points. However, their mechanical performance is often compromised by interstitial impurities, particularly oxygen, nitrogen, and carbon, which segregate to grain boundaries and promote embrittlement. In this study, we investigate the solubility and thermodynamic behavior of oxygen interstitials in a model NbTiHfTa RCCA system. We synthesized NbTiHfTa alloys with varying oxygen contents via plasma arc melting and characterized their phase evolution and microstructure using XRD, SEM, and TEM. Complementary computational modeling was performed using machine-learning interatomic potentials integrated with Monte Carlo simulations to probe oxygen interactions at the atomic scale. Our results reveal a solubility limit for oxygen between 0.8 and 1.0 atomic percentage, beyond which HfO2 formation is energetically favorable. This combined experimental-computational framework provides a predictive approach for managing interstitial behavior in RCCAs, enabling improved alloy design strategies for enhanced mechanical performance.
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All authors Aomin Huang, Siya Zhu, Calvin Belcher, Ryker Rigsby, Diran Apelian, Raymundo Arróyave, Enrique J. Lavernia

Materials Science · Cross-listed from quant-ph

Coherent and compact van der Waals transmon qubits

Jesse Balgley, Jinho Park, Xuanjing Chu et al. (+9 more)

State-of-the-art superconducting qubits rely on a limited set of thin-film materials. Expanding their materials palette can improve performance, extend operating regimes, and introduce new functionalities, but conventional thin-film fabrication hinders systematic exploration of new material combinations. Van der Waals (vdW) materials offer a highly modular crystalline platform that facilitates such exploration while enabling gate-tunability, higher-temperature operation, and compact qubit geometries. Yet it remains unknown whether a fully vdW superconducting qubit can support quantum coherence and what mechanisms dominate loss at both low and elevated temperatures in such a device. Here we demonstrate quantum-coherent merged-element transmons made entirely from vdW Josephson junctions. These first-generation, fully crystalline qubits achieve microsecond lifetimes in an ultra-compact footprint without external shunt capacitors. Energy relaxation measurements, together with microwave characterization of vdW capacitors, point to dielectric loss as the dominant relaxation channel up to hundreds of millikelvin. These results establish vdW materials as a viable platform for compact superconducting quantum devices.
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All authors Jesse Balgley, Jinho Park, Xuanjing Chu, Jiru Liu, Madisen Holbrook, Kenji Watanabe, Takashi Taniguchi, Archana Kamal, Leonardo Ranzani, Martin V. Gustafsson, James Hone, Kin Chung Fong

Materials Science

Chirality-induced magnetoresistance in hybrid organic-inorganic perovskite semiconductors

Md Azimul Haque, Pius Markus Theiler, Ian A. Leahy et al. (+14 more)

The combination of semiconducting properties and synthetically tunable chirality in chiral metal halide semiconductors (CMHS) offer a compelling platform for room temperature control over electronic spin properties, leveraging effects such as chirality-induced spin selectivity (CISS) for the development of new opto-spintronic functionalities. We report room-temperature CISS-induced magnetoresistance (CISS-MR) exceeding 100% for spin valves in a configuration consisting of a ferromagnet (FM), tunneling barrier, and CMHS. The high CISS-MR is attributed to interfacial spin-selective tunneling barrier induced by the chirality, which can produce current dissymmetry factors that surpass the limit imposed by the Jullière model governed by the intrinsic spin polarization of the adjacent FM contact. The CISS-MR exhibits a strong dependence on the CMHS composition, revealing a structure-property relationship between CISS and structural chirality. The observed exceptionally large tunneling MR response differentiates from a subtle anisotropic MR arising from the proximity effect at the FM/CMHS interface in the absence of a tunneling barrier. Our study provides insights into charge-to-spin interconversion in chiral semiconductors, offering materials design principles to control and enhance CISS response and utilize it in functional platforms.
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All authors Md Azimul Haque, Pius Markus Theiler, Ian A. Leahy, Steven P. Harvey, Jeiwan Tan, Matthew P Hautzinger, Margherita Taddei, Aeron McConnell, Andrew Greider, Andrew H. Comstock, Yifan Dong, Kirstin Alberi, Yuan Ping, Peter C. Sercel, Joseph M. Luther, Dali Sun, Matthew C. Beard

Materials Science

Magnetic properties of the Fe$_5$SiB$_2$-Fe$_5$PB$_2$ system

Daniel Hedlund, Johan Cedervall, Alexander Edström et al. (+6 more)

The magnetic properties of the compound Fe$_5$Si$_{1-x}$P$_{x}$B$_2$ have been studied, with a focus on the Curie temperature $T_\textrm{C}$, saturation magnetization $M_\textrm{S}$, and magnetocrystalline anisotropy. Field and temperature dependent magnetization measurements were used to determine $T_\textrm{C}\left(x\right)$ and $M_\textrm{S}\left(x\right)$. The saturation magnetization at 10 K (300 K) is found to monotonically decrease from $1.11~\mathrm{MA/m}$ ($1.03~\mathrm{MA/m}$) to $0.97~\mathrm{MA/m}$ ($0.87~\mathrm{MA/m}$), as $x$ increases from zero to one. The Curie temperature is determined to be 810 K and 615 K in Fe$_5$SiB$_2$ and Fe$_5$PB$_2$, respectively. The highest $T_\textrm{C}$ is observed for $x=0.1$, while it decreases monotonically for larger $x$. The Curie temperatures have also been theoretically determined to be 700 K and 660 K for Fe$_5$SiB$_2$ and Fe$_5$PB$_2$, respectively, using a combination of density functional theory and Monte Carlo simulations. The magnitude of the effective magnetocrystalline anisotropy was extracted using the law of approach to saturation, revealing an increase with increasing phosphorus concentration. Low–field magnetization vs. temperature results for $x = 0, 0.1, 0.2$ indicate that there is a transition from easy–axis to easy–plane anisotropy with decreasing temperature.
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All authors Daniel Hedlund, Johan Cedervall, Alexander Edström, Mirosław Werwinski, Sofia Kontos Olle Eriksson, Ján Rusz, Peter Svedlindh, Martin Sahlberg, Klas Gunnarsson

Materials Science · Cross-listed from quant-ph

F2: Offline Reinforcement Learning for Hamiltonian Simulation via Free-Fermionic Subroutine Compilation

Ethan Decker, Christopher Watson, Junyu Zhou et al. (+5 more)

Compiling shallow and accurate quantum circuits for Hamiltonian simulation remains challenging due to hardware constraints and the combinatorial complexity of minimizing gate count and circuit depth. Existing optimization method pipelines rely on hand-engineered classical heuristics, which cannot learn input-dependent structure and therefore miss substantial opportunities for circuit reduction. We introduce F2, an offline reinforcement learning framework that exploits free-fermionic structure to efficiently compile Trotter-based Hamiltonian simulation circuits. F2 provides (i) a reinforcement-learning environment over classically simulatable free-fermionic subroutines, (ii) architectural and objective-level inductive biases that stabilize long-horizon value learning, and (iii) a reversible synthetic-trajectory generation mechanism that consistently yields abundant, guaranteed-successful offline data. Across benchmarks spanning lattice models, protein fragments, and crystalline materials (12-222 qubits), F2 reduces gate count by 47% and depth by 38% on average relative to strong baselines (Qiskit, Cirq/OpenFermion) while maintaining average errors of 10^(-7). These results show that aligning deep reinforcement learning with the algebraic structure of quantum dynamics enables substantial improvements in circuit synthesis, suggesting a promising direction for scalable, learning-based quantum compilation
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All authors Ethan Decker, Christopher Watson, Junyu Zhou, Yuhao Liu, Chenxu Liu, Ang Li, Gushu Li, Samuel Stein

Materials Science

Intralayer antiferromagnetism in two-dimensional van der Waals magnet Fe$_3$GeTe$_2$

Neesha Yadav, Shivani Kumawat, Sandeep et al. (+2 more)

For the van der Waals magnet Fe$_3$GeTe$_2$, although a ferromagnetic ground state has been reported, there are also reports of complex magnetic behavior suggesting coexistence of ferromagnetism and antiferromagnetism due to the intricate interaction between Fe$^{+3}$ and Fe$^{+2}$ ions in this system. The exact nature of the interactions and the origin of antiferromagnetism are still under debate. Here, we report the observation of signature of ferromagnetic and antiferromagnetic couplings between different Fe-ions in the anomalous Hall effect measured for devices of mechanically exfoliated Fe$_3$GeTe$_2$ nano-flakes of thicknesses ranging from\,$\sim$\,15-20 layers. The temperature-dependent anomalous Hall effect data reveal two sharp step-like switchings at low temperature ($T\lesssim150\,$K). Our detailed analyses suggest the step-like sharp switchings in anomalous Hall resistance are due to the magnetization reversal behavior of different Fe-ions in individual layers of Fe$_3$GeTe$_2$. The experimental results can be explained by considering an intra-layer antiferromagnetic coupling between Fe$^{+3}$ and Fe$^{+3}$ ions, whereas intra-layer ferromagnetic coupling between Fe$^{+3}$ and Fe$^{+2}$ in the system. Our experimental results and the analyses are supported by the first-principles calculations for energetics and intralayer as well as interlayer exchange coupling constants.
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All authors Neesha Yadav, Shivani Kumawat, Sandeep, Brajesh Kumar Mani, Pintu Das

Materials Science

Performance Benchmarking of Tensor Trains for accelerated Quantum-Inspired Homogenization on TPU, GPU and CPU architectures

Sascha H. Hauck, Matthias Kabel and Nicolas R. Gauger

Recent advances in high-resolution CT-imaging technology are creating a new class of ultra-high resolved microstructural datasets that challenge the limits of traditional homogenization approaches. While state-of-the-art FFT-based homogenization techniques remain effective for moderate datasets, their memory footprint and computational cost grow rapidly with increasing resolution, making them progressively inefficient for industrial-scale problems. To address these challenges, the recently developed Superfast-Fourier Transform (SFFT)-based homogenization algorithm leverages the memory-efficient low-rank representations of Tensor Trains (TTs), which reduce the storage and computational requirements of large-scale homogenization problems. Developed for CPU usage, SFFT-based Homogenization efficiently handles high-resolution datasets, assuming the underlying data is well-behaved. In this work, we investigate the performance of fundamental TT operations on modern hardware accelerators using the JAX framework. A benchmarking study across CPUs, GPUs, and TPUs evaluates execution times and computational efficiency, highlighting the strengths and limitations of TT operations on different architectures and motivating future hybrid approaches. Building on these insights, we adapt the SFFT-based homogenization algorithm for accelerator execution, enabling homogenization at high resolutions ranging from 300 million to 70 billion grid points, which are infeasible for the best available GPU-based FFT reference implementation. While the observed scaling behavior is geometry-dependent, the results demonstrate the potential of accelerator-based quantum-inspired homogenization for high-performance multiscale simulations.
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Materials Science

Bimorph Lithium Niobate Piezoelectric Micromachined Ultrasonic Transducers

Vakhtang Chulukhadze, Zihuan Liu, Ziqian Yao et al. (+8 more)

Piezoelectric micromachined ultrasonic transducers (PMUTs) are widely utilized in applications that demand mechanical resilience, thermal stability, and compact form factors. Recent efforts have sought to demonstrate that single-crystal lithium niobate (LN) is a promising PMUT material platform, offering high electromechanical coupling (k2) and bidirectional performance. In addition, advances in LN film transfer technology have enabled high quality periodically poled piezoelectric films (P3F), facilitating a bimorph piezoelectric stack without intermediate electrodes. In this work, we showcase a bimorph PMUT incorporating a mechanically robust, 20 $\mu$m thick P3F LN active layer. We establish the motivation for LN PMUTs through a material comparison, followed by extensive membrane geometry optimization and subsequent enhancement of the PMUT's k2. We demonstrate a 775 kHz flexural mode device with a quality factor (Q) of 200 and an extracted k2 of 6.4%, yielding a high transmit efficiency of 65 nm/V with a mechanically robust active layer. We leverage the high performance to demonstrate extreme-temperature resilience, showcasing stable device operation up to 600 $^\circ$C and survival up to 900 $^\circ$C, highlighting LN's potential as a resilient PMUT platform.
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All authors Vakhtang Chulukhadze, Zihuan Liu, Ziqian Yao, Lezli Matto, Tzu-Hsuan Hsu, Nishanth Ravi, Xiaoyu Niu, Michael E. Liao, Mark S. Goorsky, Neal Hall, Ruochen Lu

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

Extreme Strain Controlled Correlated Metal-Insulator Transition in the Altermagnet CrSb

Cong Li, Mengli Hu, Jianfeng Zhang et al. (+14 more)

Correlated flat bands and altermagnetism are two important directions in quantum materials, centred respectively on interaction-dominated phases and symmetry-enforced spin-textured states, yet both derive from lattice symmetry and orbital hybridization. This common origin implies that extreme crystal distortion, by narrowing bandwidths, enhancing correlations and reshaping the symmetries of altermagnetic spin splittings, could unify flat-band and altermagnetic physics in a single material; in practice, however, achieving such large distortions in a crystalline altermagnet is a formidable challenge. Here we combine a dedicated strain device with a tailored single-crystal mounting scheme to impose a highly tensile strain gradient in bulk CrSb, a prototypical altermagnet, creating a near-surface layer in which the in-plane lattice is strongly distorted relative to the weakly strained bulk, while the average bulk distortion remains small. Angle-resolved photoemission reveals a reversible regime at moderate strain, where a deeper flat-band feature, attributed to a strain-gradient-driven suppression of Cr-Sb hybridization, coexists with a correlation-enhanced Cr 3d flat band, and an irreversible regime at larger strain where partial bond decoupling drives a predominantly insulating spectral response. Density-functional calculations show that an orbital-selective altermagnetic spin texture persists across this correlated regime despite strong bandwidth renormalisation. These results define a strain-symmetry-correlation map for CrSb and establish extreme tensile strain as a route to co-engineer flat-band tendencies and spin-textured, zero-net-moment correlated states in altermagnets, pointing toward strain-adaptive, spin-selective Mott filtering and related device concepts.
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All authors Cong Li, Mengli Hu, Jianfeng Zhang, Magnus H. Berntsen, Francesco Scali, Dibya Phuyal, Chun Lin, Wanyu Chen, Johan Chang, Oliver J. Clark, Timur K. Kim, Jacek Osiecki, Craig Polley, Balasubramanian Thiagarajan, Zhilin Li, Tao Xiang, Oscar Tjernberg

Materials Science

Network of localized magnetic textures revealed using a saddle-point search framework

Hendrik Schrautzer, Tim Drevelow, Hannes Jónsson et al. (+1 more)

A computational framework is presented for the exploration of energy surfaces of magnetic systems via systematic identification of first-order saddle points that connect local energy minima representing possible states of the system. The saddle points characterize the mechanism of transitions between states and, together with the energy of the local minima, provide estimates of the transition rates within harmonic transition state theory or Kramers/Langer theory. The calculations involve four stages: (1) the symmetry of a given energy-minimum configuration is identified and used to define subsystems whose eigenmodes provide relevant deformation directions. (2) These modes are then used to guide the system toward the neighborhoods of the various saddle points on the energy rim surrounding the given energy minimum. (3) Next, the geodesic minimum mode following method is employed to efficiently converge onto the saddle points. (4) Finally, the identified saddle points are embedded into the network describing the connectivity of the states of the system. This methodology is applied in a study of the metastable textures of two-dimensional chiral magnets described by a lattice Hamiltonian, where a hierarchy of transition mechanisms for the nucleation, annihilation, and rearrangement of various localized magnetic textures are identified, such as skyrmions, antiskyrmions, skyrmion bags, chiral droplet, etc. Transitions corresponding to homotopies that preserve the topological charge as well as transformations that change it are identified. By scaling the interaction parameters, the distinct behavior of these two classes is obtained as the continuum limit is approached. For some transitions, the topological charge changes during the transition even though it is the same for the initial and final states.
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All authors Hendrik Schrautzer, Tim Drevelow, Hannes Jónsson, Pavel F. Bessarab

Materials Science

Computational Studies on O2-P2 Phase-Transition Dynamics in Layered-Oxide Sodium-Ion Cathode Materials

Konstantin Köster and Payam Kaghazchi

Sodium-ion batteries have gained much interest over the past years and especially layered oxides are highly considered as cathodes for the next generation of batteries. However, there are still significant challenges to overcome in these materials for practical applications mainly related to capacity degradation and voltage fading. A key influence factor for these challenges are phase transitions that occur by gliding of layers during operation of these materials. Until now there is limited atomistic-level understanding on such transitions as simulations of these processes are computationally demanding. In this work, we trained a classical pairwise Coulomb-Buckingham potential versus extensive ab initio data using a genetic algorithm to study O2-P2 phase transitions in Na\textsubscript{x}CoO\textsubscript{2}. Our density functional theory~(DFT) and classical potential calculations show that phase transition barriers decrease upon desodiation and are further lowered if dynamic conditions are considered through molecular dynamics simulations. Our developed classical potential is able to capture phase transitions and its related increase in the Na-ion diffusivity under standard lab conditions at the $\upmu$s timescale of molecular dynamics simulation. Furthermore, it is found that the phase transition occurs gradually via various OPn phases.
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Materials Science · Cross-listed from physics.app-ph

Optimization for growth condition of ultrathin hexagonal boron nitride on dielectric substrates via LPCVD

Meryem Bozkaya, Muhammet Nasuh Ar{\i}k, Ali Altuntepe et al. (+2 more)

Hexagonal Boron Nitride (h-BN) is a highly intriguing candidate for heterostructure optoelectronic applications, such as Deep Ultraviolet photodetectors, UV sensing and communication systems and solar cells. This is primarily due to its unique properties, including a layer dependent wide energy bandgap, superior mechanical strength, high thermal conductivity, high band-edge absorption coefficient, and exceptional transparency in the UV region. The widely adopted synthesis method for h-BN thin films is Chemical Vapor Deposition (CVD) Method, which often utilizes catalytic substrates like copper (Cu) and Nickel (Ni). However, integrating the synthesized h-BN into device applications requires a subsequent transfer process to the target substrate. This transfer step introduces significant material damage, such as folding, cracking and polymer residues, which ultimately degrade the optoelectronic properties of the material and compromise device performance. To overcome this major challenge, there is a strong need to synthesize high-quality h-BN films directly onto dielectric substrates such as silicon (Si), SiO2, quartz, sapphire or AlN without the need for transfer. The primary difficulty in direct synthesis lies in achieving homogenous, high crystallinity films with controllable thickness due to the absence of a catalytic effect. In this work, we investigated the optimization of growth parameters for the direct synthesis of ultrathin h-BN films on non-catalytic quartz substrates, which are highly transparent in the UV region, using the Low-pressure Chemical Vapor Deposition (LPCVD) method. The optimal synthesis conditions were determined to be 1050oC for 60 min, achieved by the decomposition of 150 mg Ammonia Borane (AB) precursor at 80oC. This optimization is crucial for advancing large-scale, high-performance h-BN based DUV photodetector fabrication.
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All authors Meryem Bozkaya, Muhammet Nasuh Ar{\i}k, Ali Altuntepe, Hakan Ateş, Recep Zan

Materials Science

Mid-infrared intraband transitions in InAs colloidal quantum dots

Shraman Kumar Saha and Philippe Guyot-Sionnest

III-V colloidal quantum dots are widely studied for their applications as detectors and emitters from visible to short-wave infrared. They might also be used in the mid-infrared if they can be stably n-doped to access their intraband transitions. Mid-infrared intraband transitions are therefore studied for InAs, InAs/InP, and InAs/ZnSe colloidal quantum dots with an energy gap at 1.4 micron. Using electrochemistry, the quantum dot films show state-resolved mobility, state-resolved electron filling, and intraband absorption in the 3-8 micron range. The InAs/ZnSe films need a more reducing potential than InAs, but the InAs/InP films need a lower reduction potential. As a result, we found that dry films of InAs/InP dots show stable n-doping of the 1Se state, with a steady-state intraband absorption in the 3-5 micron range, and intraband luminescence at 5 micron. low-toxicity, high thermal stability, and stable n-doping, InAs quantum dots become an interesting material for mid-infrared applications.
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