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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Saturday 4 October

Materials Science

Electro-optic effects in some sliding ferroelectrics

Xueqing Wan, Zhenlong Zhang, Charles Paillard et al. (+4 more)

Sliding ferroelectrics, which exhibit out-of-plane polarization arising from specific stacking rather than conventional ionic displacements, are new types of ferroelectrics whose underdeveloped physics needs to be explored. Here, we investigate the electro-optic (EO) response of these materials using first-principles calculations, focusing on ZrI$_{2}$ as a prototype. We reveal that, contrary to conventional ferroelectrics, the EO effect in ZrI$_{2}$ is dominated by its electronic contribution rather than the ionic one, which promises faster EO responses. Furthermore, both biaxial and uniaxial strains significantly enhance this response, and a universal-like linear relationship between the band gap and such response is discovered. We also report a large elasto-optic coefficient that is independent of biaxial strain. Similar large linear EO coefficients and properties are found in other sliding ferroelectrics, including different zirconium dihalides, as well as BN and BP bilayers. These findings highlight sliding ferroelectrics as highly promising candidates for ultrafast nonlinear optical devices and reveal unusual mechanisms.
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All authors Xueqing Wan, Zhenlong Zhang, Charles Paillard, Jinyang Ni, Lei Zhang, Zhijun Jiang, Laurent Bellaiche

Materials Science

In situ elucidation of mechanisms governing crack transition to plasticity arrest

Abdalrhaman Koko, Bemin Sheen, Caitlin Green et al. (+1 more)

Despite extensive theoretical treatment of short- to long-crack transitions, direct experimental quantification of how elastic and plastic energy contributions evolve at the crack tip during arrest has remained absent. In this study, we present an in situ investigation of crack propagation in cold-worked AA-5052 using high-resolution scanning electron microscopy digital image correlation (SEM-DIC) and electron backscatter diffraction (EBSD). By reconstructing local crack-tip fields from measured displacement data, we extract mode I and II stress intensity factors and both elastic and elastoplastic energy release rates ({\Delta}JE and {\Delta}Jp). The results show that microstructure-sensitive cracks propagate in a mixed-mode manner at low driving force and transition to plasticity-dominated and load-aligned crack, arrested as the crack-tip process zone develops and expands multiple grains. This transition is identified through the divergence of elastic and elastoplastic energy measures ({\Delta}JE >= {\Delta}JP), crack-tip blunting, slip-band emission, and the emergence of localised plastic deformation. These findings demonstrate that crack arrest coincides with a measurable transition in crack-tip energy partitioning and with process-zone expansion beyond grain-scale dimensions. The results establish an experimentally measurable energy-partition criterion for crack arrest and demonstrate that fracture regime transition is governed by
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All authors Abdalrhaman Koko, Bemin Sheen, Caitlin Green, Fionn Dunne

Materials Science

Hierarchically Engineered Titanium Suboxide Films for High-Efficiency Solar Thermal Conversion

Silpa S, Ann Eliza Joseph, Srinivas G et al. (+2 more)

We report the development of broadband solar absorber coatings based on titanium suboxide composite thin films on aluminium substrates. The films are fabricated via scalable DC magnetron sputtering using a Ti target, followed by post-annealing in a fixed $O_2$ partial pressure of 0.45 mbar. By tuning deposition time and annealing temperature, a composite phase of $Ti_2O_3$ and $TiO_2$ was achieved. The Raman mapping of the films substantiates the distribution and coexistence of the two phases. The optimized sample, deposited for 10 min and annealed at 500 $^oC$, exhibited a superior solar absorptance (${\alpha}_s$ = 0.913) and optimally low thermal emittance (${\epsilon}_t$ = 0.11). Nevertheless, the 15- and 20-min deposited films also showed a promising absorptance (>0.85) and emittance values (<0.13). Morphological studies revealed island-type nanostructures, leading to enhanced photothermal performance via electric field confinement, which is validated by optical simulations. This work provides a promising route toward efficient, scalable, and cost-effective spectrally selective solar absorbers for solar thermal applications.
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All authors Silpa S, Ann Eliza Joseph, Srinivas G, Harish C Barshilia, Vinayak B Kamble

Materials Science

New Directions in Focused Ion Beam Induced Deposition for the Nanoprinting of Functional 3D Heterostructures

Frances Isabel Allen

The focused ion beam (FIB) microscope is well established as a high-resolution machining instrument capable of site-selectively removing material down to the nanoscale. Beyond subtractive processing, however, the FIB can also add material using a technique known as focused ion beam induced deposition (FIBID), enabling the direct-write of complex nanostructures. This work explores new directions in three-dimensional nanoprinting with FIBID, harnessing unique features of helium and neon FIBs to fabricate nanoscale heterostructures, including multimaterial architectures and deposits with engineered internal voids. Detailed insight into the chemical and structural composition of these nanostructures is obtained using advanced electron microscopy, revealing buried interfaces and material transformations. Building on these results, the evolution of FIBID into a versatile platform for functional nanomaterials design is discussed, opening pathways toward next-generation nanoscale devices and technologies.
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Friday 3 October

Materials Science · Cross-listed from physics.flu-dyn

Adhesive forces in droplet kinetic friction

Glen McHale, Sara Janahi, Hernán Barrio-Zhang et al. (+4 more)

Kinetic frictional forces resisting droplet motion often appear to be separate to surface wettability and adhesive forces. Here we show that such friction arises from a simple combination of the contact angle hysteresis and adhesive force. We show theoretically, and confirm using tilt angle experiments of droplets on liquid-like surfaces, the dependence of the coefficient of droplet-on-solid kinetic friction on system parameters. We also show that a molecular kinetic-type model can describe the observed non-linear velocity-force relationship. Our findings provide a fundamental understanding of the relationship between droplet-on-solid friction, and wettability and liquid adhesion.
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All authors Glen McHale, Sara Janahi, Hernán Barrio-Zhang, Yaofeng Wang, Jinju Chen, Gary G. Wells, Rodrigo Ledesma-Aguilar

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

High-spin magnetic ground states of neutral dopant clusters in semiconductors

Rhine Samajdar, Haonan Zhou and R. N. Bhatt

High-spin states hold significant promise for classical and quantum information storage and emerging magnetic memory technologies. Here, we present a systematic framework for engineering such high-spin magnetic states in dopant clusters formed from substitutional impurities in semiconductors. In single-valley materials such as gallium arsenide, impurity states are hydrogenic and exchange interactions generally favor low-spin configurations, except in special geometries. In contrast, multivalley semiconductors exhibit oscillatory form factors in their exchange couplings, enabling the controlled suppression of selected hopping processes and exchange couplings. Exploiting this feature, we demonstrate how carefully arranged impurities in aluminum arsenide, germanium, and silicon can stabilize ground states with a net spin that scale extensively with system size. Within effective mass theory and the tight-binding approximation for hopping, we construct explicit examples ranging from finite clusters to extended lattices and fractal-like tilings. In two dimensions, we identify several favorable dopant geometries supporting a net spin equal to around half of the fully polarized value in the thermodynamic limit, including one which achieves over $70\%$ polarization. Our results provide a general design principle for harnessing valley degeneracy in semiconductors to construct robust high-spin states and outline a pathway for their experimental realization via precision implantation of dopants.
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Materials Science

Strain Effects on Electronic Properties of Cobalt-Based Coordination Nanosheets

Kento Nishigomi, Yu Yi, Souren Adhikary et al. (+2 more)

We theoretically study the strain effects on the electronic properties of cobalt-based benzenehexathiol (CoBHT) coordination nanosheets using first-principles calculations. Two distinct crystal structures, high-density structure (HDS) and low-density structure (LDS), are explored. Our results reveal that HDS behaves as a metal, while LDS exhibits semiconducting. Spin-polarized electronic band structures highlight the presence of energy band structures of Kagome lattice, and the inclusion of spin-orbit coupling (SOC) results in band gap openings at high-symmetric K points. Furthermore, we construct the tight-binding model to investigate the topological properties of CoBHT, demonstrating anomalous Hall conductivity driven by the intrinsic Berry curvature. The impact of uniaxial strain on the electronic and magnetic properties of CoBHT is also studied. Strain induces significant modifications in magnetic moments and density of states, particularly in the HDS. Anomalous Hall conductivity is enhanced under hole-doping conditions, suggesting that strain can be used to tailor the electronic properties of CoBHT for specific applications. Our findings underscore the potential of CoBHT nanosheets for use in next-generation electronic, optoelectronic, and catalytic devices with tunable properties through strain engineering.
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All authors Kento Nishigomi, Yu Yi, Souren Adhikary, Kazuhito Tsukagoshi, Katsunori Wakabayashi

Materials Science

Bloch Oscillations and Landau-Zener Transitions in Flat-Band Lattices with Quadratic and Linear Band Touchings

Chenhaoyue Wang, Carlos J. Garcia-Cervera and Amartya S. Banerjee

Bloch oscillations (BOs) describe the coherent oscillatory motion of electrons in a periodic lattice under a constant external electric field. Deviations from pure harmonic wave packet motion or irregular Bloch oscillations can occur due to Zener tunneling (Landau-Zener Transitions or LZTs), with oscillation frequencies closely tied to interband coupling strengths. Motivated by the interplay between flat-band physics and interband coupling in generating irregular BOs, here we investigate these oscillations in Lieb and Kagome lattices using two complementary approaches: coherent transport simulations and scattering matrix analysis. In the presence of unavoidable band touchings, half-fundamental and fundamental BO frequencies are observed in Lieb and Kagome lattices, respectively – a behavior directly linked to their distinct band structures. When avoided band touchings are introduced, distinct BO frequency responses to coupling parameters in each lattice are observed. Scattering matrix analysis reveals strong coupling and potential LZTs between dispersive bands and the flat band in Kagome lattices, with the quadratic band touching enhancing interband interactions and resulting in BO dynamics that is distinct from systems with linear crossings. In contrast, the Lieb lattice – a three level system – shows independent coupling between the flat band and two dispersive bands, without direct LZTs occurring between the two dispersive bands themselves. Finally, to obtain a unifying perspective on these results, we examine BOs during a strain-induced transition from Kagome to Lieb lattices, and link the evolution of irregular BO frequencies to changes in band connectivity and interband coupling.
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Materials Science · Cross-listed from cs.LG

Training Variation of Physically-Informed Deep Learning Models

Ashley Lenau, Dennis Dimiduk and Stephen R. Niezgoda

A successful deep learning network is highly dependent not only on the training dataset, but the training algorithm used to condition the network for a given task. The loss function, dataset, and tuning of hyperparameters all play an essential role in training a network, yet there is not much discussion on the reliability or reproducibility of a training algorithm. With the rise in popularity of physics-informed loss functions, this raises the question of how reliable one's loss function is in conditioning a network to enforce a particular boundary condition. Reporting the model variation is needed to assess a loss function's ability to consistently train a network to obey a given boundary condition, and provides a fairer comparison among different methods. In this work, a Pix2Pix network predicting the stress fields of high elastic contrast composites is used as a case study. Several different loss functions enforcing stress equilibrium are implemented, with each displaying different levels of variation in convergence, accuracy, and enforcing stress equilibrium across many training sessions. Suggested practices in reporting model variation are also shared.
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Materials Science · Cross-listed from physics.chem-ph

Mixed Stochastic-Deterministic Density Functional Theoretic Decomposition of Kubo-Greenwood Conductivities in the Projector Augmented Wave Formalism

Vidushi Sharma, Lee A. Collins and Alexander J. White

Pairing the accuracy of Kohn-Sham density-functional framework with the efficiency of a stochastic algorithmic approach, mixed stochastic-deterministic Density Functional Theory (mDFT) achieves a favorable computational scaling with system sizes and electronic temperatures. We employ the recently developed mDFT formalism to investigate the dynamic charge-transport properties of systems in the warm dense matter regime. The optical conductivity spectra are computed for single- and multi- component mixtures of carbon, hydrogen, and beryllium using two complementary approaches: Kubo-Greenwood in the mDFT picture and real-time Time-Dependent mDFT. We further devise a decomposition of the Onsager coefficients leading up to the Kubo-Greenwood spectra to exhibit contributions from the deterministic, stochastic, and mixed electronic state transitions at different incident photon energies.
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Materials Science

Sliding multiferroicity in hexagonal stacked CrI3

Carter Fox, Jose D. Mella, Jack Rollins et al. (+11 more)

Developing new multiferroics at the two-dimensional (2D) limit with energy-efficient magnetoelectric coupling can inform the interplay physics of novel orders and advance on-chip high-performance computing applications. Here we apply stacking order engineering to create a new type of 2D multiferroics, namely sliding multiferroics, based on polar hexagonal stacked (H-stacked) CrI3. This new stacking order removes structural inversion symmetry and gives rise to room temperature sliding ferroelectricity, as confirmed by Raman spectroscopy, second harmonic generation spectroscopy and electrical transport measurements. Building upon the gate-dependent reflective magnetic circular dichroism, first-principles calculations, and modeling, sliding ferroelectricity is shown to interplay with an emergent interfacial ferromagnetism via interlayer spin-polarized charge transfer. This coupling mechanism results in non-volatile magnetic switching by as low as 0.4V across the H-stacked CrI3. Our demonstration introduces polar stacking order engineering of 2D magnets as a general approach to create non-volatile 2D multiferroics with efficient magnetoelectric coupling, paving the way for low-power electronics and spintronics at the atomically thin limit.
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All authors Carter Fox, Jose D. Mella, Jack Rollins, Yangchen He, Yulu Mao, Haotian Jiang, Alaina Drew, Hongrui Ma, Takashi Taniguchi, Kenji Watanabe, Ying Wang, Daniel Rhodes, Salvador Barraza-Lopez, Jun Xiao

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

Heterogeneous dynamics in a polymer solution revealed through measurement of ultraslow convection

Thomas P. Chaney, Samuel D. Marks, Dylan M. Ladd et al. (+9 more)

Understanding solution-phase aggregation and dynamics in complex fluids is critical for material processing, yet widely used dynamic light scattering (DLS) fails for strongly attenuating systems such as conjugated polymers. We use X-ray photon correlation spectroscopy (XPCS) to probe the dynamics of a polymer, PM7, in toluene, revealing unexpected oscillations in the autocorrelation function that show vertical flow during measurement. Despite the relatively low X-ray absorption, measured flow velocities scale with X-ray beam power and suggest convective transport. Our analyses reveal both mobile and static scatterers that together produce oscillatory, heterodyne features in the measured correlation functions. Finite element simulations predict flow velocities much larger than observed, suggesting that entanglements of the aggregates slow their motion. These results provide a direct measurement of ultra-slow convection and highlight the need to explicitly account for even modest beam heating in interpreting XPCS results. Moreover, the observation of distinct scatterer populations underscores the structural complexity of conjugated polymer solutions.
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All authors Thomas P. Chaney, Samuel D. Marks, Dylan M. Ladd, Andrei Fluerasu, Federico Zontone, Yuriy Chushkin, Sebastian Frücht, Dina Sheyfer, Kelsey Levine, Amnahir E. Peña-Alcántara, Hans-Georg Steinrück, Michael F. Toney

Materials Science

Thermal assisted transport of biexcitons in monolayer WSe2

Dorian Béret, Louka Hemmen, Vishwas Jindal et al. (+9 more)

Studies of excitonic transport in transition metal dichalcogenide monolayers have attracted increasing interest in recent years in order to develop nano-optoelectronic devices made with 2D materials. These studies began with low to moderate optical excitation regimes, and more recently have focused on high injection regimes where nonlinear effects appear. This article is focused on the transport of biexcitons by spatially and temporally resolved photoluminescence spectroscopy at high excitation flux. The study is carried out on a high-quality WSe$_2$ monolayer encapsulated in hexagonal boron nitride. The results show that a Seebeck current affects transport in connection with the presence of hot biexcitons. In particular, we observe the formation of spatial rings, also called halos, which have been observed in other excitonic gases. These results tend to generalize the importance of high-energy populations in excitonic transport in TMD, even for complex and heavy excitonic particles.
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All authors Dorian Béret, Louka Hemmen, Vishwas Jindal, Sreyan Raha, Thierry Amand, Delphine Lagarde, Andrea Balocchi, Cédric Robert, Helene Carrere, Xavier Marie, Pierre Renucci, Laurent Lombez

Materials Science

Electrically modulated light-emitting diodes driven by resonant and antiresonant tunneling between Cr$_2$Ge$_2$Te$_6$ electrodes

Natalia Zawadzka, Kristina Vaklinova, Tomasz Woźniak et al. (+7 more)

Exploring the electron tunneling mechanisms in diverse materials systems constitutes a versatile strategy for tailoring the properties of optoelectronic devices. In this domain, bipolar vertical tunneling junctions composed of van der Waals materials with vastly different electronic band structures enable simultaneous injection of electrons and holes into an optically active material, providing a universal blueprint for light-emitting diodes (LEDs). Efficient modulation of the injection efficiency has previously been demonstrated by creating resonant states within the energy barrier formed by the luminescent material. Here, we present an alternative approach towards resonant tunneling conditions by fabricating tunneling junctions composed entirely from gapped materials: Cr$_2$Ge$_2$Te$_6$ as electrodes, hBN as a tunneling barrier, and monolayer WSe$_2$ as a luminescent medium. The characterization of such LEDs revealed a nonmonotonous evolution of the electroluminescence intensity with the tunneling bias. The dominant role driving the characteristics of the electron tunneling was associated with the relative alignment of the density of states in Cr$_2$Ge$_2$Te$_6$ electrodes. The unique device architecture introduced here presents a universal pathway towards LEDs operating at room temperature with electrically modulated emission intensity.
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All authors Natalia Zawadzka, Kristina Vaklinova, Tomasz Woźniak, Mihai I. Sturza, Holger Kohlmann, Kenji Watanabe, Takashi Taniguchi, Adam Babiński, Maciej Koperski, Maciej R. Molas

Materials Science

Structural Chirality and Natural Optical Activity across the $\alpha$-to-$\beta$ Phase Transition in SiO$_2$ and AlPO$_4$ from first-principles

F. Gómez-Ortiz, A. Zabalo, A. M. Glazer et al. (+3 more)

Natural optical activity (NOA), the ability of a material to rotate the plane of polarized light, has traditionally been associated with structural chirality. However, this relationship has often been oversimplified, leading to conceptual misunderstandings, particularly when attempts are made to directly correlate structural handedness with optical rotatory power. In reality, the relationship between chirality and NOA is more nuanced: optical activity can arise in both chiral and achiral crystal structures, and the sign of the rotation cannot necessarily be inferred from the handedness of the space group. % In this work, we conduct a first-principles investigation of natural optical activity in SiO$_2$ and AlPO$_4$ crystals, focusing on their enantiomorphic structural phase transition from high-symmetry hexagonal ($P6_422$ or $P6_222$) to low-symmetry trigonal ($P3_121$ or $P3_221$) space groups. This transition, driven by the condensation of a zone-center $\Gamma_3$ phonon mode, reverses the screw axis type given by the space group symbol while leaving the sign of the optical activity unchanged. By following the evolution of the structure and the optical response along the transition pathway, we clarify the microscopic origin of this behavior. We demonstrate that the sense of optical rotation is determined not by the nominal helicity of the screw axis given in the space group symbol, but by the atomic-scale helicity of the most polarizable atoms of the structure.
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All authors F. Gómez-Ortiz, A. Zabalo, A. M. Glazer, E. E. McCabe, A. H. Romero, E. Bousquet

Materials Science

Subthermal Mean Transverse Energies Induced by Electron Refraction on the Jump in Mass at the Surface of Multialkali Photocathodes

S.A. Rozhkov, V.V. Bakin, H.E. Scheibler et al. (+6 more)

The search for photocathode materials with low mean transverse energies (MTEs) and, hence, low intrinsic emittance is of crucial importance for various fields of particle and solid state physics. Here, we demonstrate that polycrystalline multialkali Na$_{2}$KSb(Cs,Sb) photocathodes with negative effective electron affinity (NEA) have MTE values at room temperature by a factor of 2 lower than those of monocrystalline p-GaAs(Cs,O) photocathodes. These low MTE values are due to the electron refraction on the jump in mass, between a small effective mass in Na$_{2}$KSb and free electron mass in vacuum. It is proved that, at the NEA state, up to half of photoelectrons are emitted in a narrow-angle cone with the fractional MTE of 9\,meV at room temperature. We also showed that the transition from NEA to positive effective affinity results in the subthermal total MTE of the Na$_{2}$KSb(Cs,Sb) photocathode, along with quantum efficiency of about 10$^{-2}$. The physical reasons for the manifestation of the refraction effect in multialkali photocathodes are discussed, opening up opportunities for the development of high-brightness and ultracold robust electron sources.
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All authors S.A. Rozhkov, V.V. Bakin, H.E. Scheibler, V.S. Rusetsky, D.V. Gorshkov, D.A. Kustov, V.A. Golyashov, V.L. Alperovich, O. E. Tereshchenko

Materials Science

Redox Chemistry of LiCoO$_2$, LiNiO$_2$, and LiNi$_{1/3}$Mn$_{1/3}$Co$_{1/3}$O$_2$ Cathodes: Deduced via XPS, DFT+DMFT, and Charge Transfer Multiplet Simulations

Ruiwen Xie, Maximilian Mellin, Wolfram Jaegermann et al. (+3 more)

Understanding the evolution of the physicochemical bulk properties during the Li deintercalation (charging) process is critical for optimizing battery cathode materials. In this study, we combine X-ray photoelectron spectroscopy (XPS), density functional theory plus dynamical mean-field theory (DFT+DMFT) calculations, and charge transfer multiplet (CTM) model simulations to investigate how hybridization between transition metal (TM) 3d and oxygen 2p orbitals evolves with Li deintercalation. Based on the presented approach combining theoretical calculations and experimental studies of pristine and deintercalated cathodes, two important problems of ion batteries can be addressed: i) the detailed electronic structure and involved changes with deintercalation providing information of the charge compensation mechanism, and ii) the precise experimental analysis of XPS data which are dominated by charge transfer coupled to final-state effects affecting the satellite structure. As main result for the investigated Li TM oxides, it can be concluded that the electron transfer coupled to the Li$^{+}$-ion migration does not follow a rigid band model but is modified due to changes in TM 3d and O 2p states hybridization. Furthermore, this integrated approach identifies the 2p XPS satellite peak intensity of TM as an effective indicator of the redox chemistry. With that the redox chemistry of cathodes can be deduced, thus offering a foundation for designing more efficient battery materials.
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All authors Ruiwen Xie, Maximilian Mellin, Wolfram Jaegermann, Jan P. Hofmann, Frank M. F. de Groot, Hongbin Zhang

Materials Science

A physics-informed neural network approach to the point defect model for electrochemical oxide film growth

Mohid Farooqi, Ingmar Bösing and Conrard G. Tetsassi Feugmo

Physics-informed neural networks (PINNs) offer a novel AI-driven framework for integrating physical laws directly into neural network models, facilitating the solution of complex multiphysics problems in materials engineering. This study systematically explores the application of PINNs to simulate oxide film layer growth in halide-free solutions using the point defect model (PDM). We identify and analyze four key failure modes in this context: imbalanced loss components across different physical processes, numerical instabilities due to variable scale disparities, challenges in enforcing boundary conditions within multiphysics systems, and convergence to mathematically valid but physically meaningless solutions. To overcome these challenges, we implement and validate established techniques including nondimensionalization for training stabilization, Neural Tangent Kernel-based adaptive loss balancing, robust enforcement of boundary conditions and hybrid training with sparse data. Our results demonstrate the effectiveness of these strategies in enhancing the reliability and physical fidelity of PINNs, achieving sub $1\%$ relative error as compared to Finite Element Benchmarks with the hybrid model. Thereby showing that PINNs can be used for high fidelity electrochemical simulations with minimal data requirements and highlight necesary factors for fully autonomous PINN simulations.
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Materials Science

Photovoltaic Performance of a Rotationally Faulted Multilayer Graphene/n-Si Schottky Junction

Hojun Im and Masahiro Teraoka

We report the fabrication and photovoltaic performance of a rotationally faulted multilayer graphene (rf-MLG)/n-Si Schottky junction device. A thickness-controlled rf-MLG is synthesized using a 5 {\mu}m Ni foil catalyst via the chemical vapor deposition method and transferred to the n-Si substrate via a polymer-free process, enabling facile and cost-effective fabrication. The device demonstrates an ideality factor of 1.67, a rectification factor of approximately 4x10^5 at {\pm}1.0 V, and a Schottky barrier height of 0.83 eV. A strong linear relationship between light intensity and photocurrent is also observed. Furthermore, the device exhibits a peak external quantum efficiency of ~26% at 540 nm and a peak internal quantum efficiency of ~97% at 410 nm. Transient photocurrent and photovoltaic measurements show approximately one-microsecond extraction and several-millisecond recombination times, respectively, revealing effective charge collection for photovoltaic applications. These results indicate that the rf-MLG/n-Si Schottky junction is well-formed and achieves performance comparable to that of SLG devices, demonstrating its potential for optoelectronic applications.
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Materials Science · Cross-listed from cond-mat.mes-hall

Magnetocaloric effect for the altermagnetic candidate MnTe

N.N. Orlova, V.D. Esin, A.V. Timonina et al. (+2 more)

We experimentally investigate magnetocaloric effect for single crystals of MnTe altermagnet at the transition to the state with spontaneous spin polarization, i.e. well below the Néel temperature of MnTe. The isothermal magnetic entropy change $\Delta S$ is calculated from the experimental magnetization curves by using Maxwell relation. We observe well-defined magnetocaloric effect as a narrow $\Delta S$ peak around the cricital temperature $T_c\approx 81$~K, which is accompanied by sharp magnetization jump. This behavior is unusual for standard ferromagnetic transitions, so it confirms the predicted spin-orbit-induced spin polarization in the MnTe altermagnetic state.
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All authors N.N. Orlova, V.D. Esin, A.V. Timonina, N.N. Kolesnikov, E.V. Deviatov

Materials Science

Kolmogorov-Arnold Networks in Thermoelectric Materials Design

Marco Fronzi, Michael J. Ford, Kamal Singh Nayal et al. (+2 more)

The discovery of high-performance thermoelectric materials requires models that are both accurate and interpretable. Traditional machine learning approaches, while effective at property prediction, often act as black boxes and provide limited physical insight. In this work, we introduce Kolmogorov–Arnold Networks (KANs) for the prediction of thermoelectric properties, focusing on the Seebeck coefficient and band gap. Compared to multilayer perceptrons (MLPs), KANs achieve comparable predictive accuracy while offering explicit symbolic representations of structure–property relationships. This dual capability enables both reliable predictions and the extraction of physically meaningful functional forms. Benchmarking against literature models further highlights the robustness and generalisability of the approach. Our findings demonstrate that KANs provide a powerful framework for reverse engineering materials with targeted thermoelectric properties, bridging the gap between predictive performance and scientific interpretability.
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All authors Marco Fronzi, Michael J. Ford, Kamal Singh Nayal, Olexandr Isayev, Catherine Stampfl

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

Ginzburg-Landau theory of spin pumping through an antiferromagnetic layer near the Néel temperature

Yuto Furutani, Hayato Fukushima, Yutaka Yamamoto et al. (+2 more)

Spin pumping is a microwave-driven means for injecting spins from a ferromagnet into the adjacent target material. The insertion of a thin antiferromagnetic layer between the ferromagnet and the target material is known to enhance the spin pumping signal. Here, in view of describing dynamic fluctuations of the Néel order parameter, we develop Ginzburg-Landau theory of the spin pumping in a ferromagnet/antiferromagnet/heavy metal trilayer in the vicinity of the antiferromagnetic Néel temperature $T_{\rm N}$. When there exists an interfacial exchange interaction between the ferromagnetic spins and the antiferromagnetic Néel order parameter at the ferromagnet/antiferromagnet interface, we find a strongly frequency-dependent enhancement of the pumped spin current that is peaked at $T_{\rm N}$. The present finding offers an explanation for the enhanced spin pumping with strong frequency dependence observed in a Y$_3$Fe$_5$O$_{12}$/CoO/Pt system.
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All authors Yuto Furutani, Hayato Fukushima, Yutaka Yamamoto, Masanori Ichioka, Hiroto Adachi

Thursday 2 October

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

Impact of Switching Layer Architecture on Power Consumption in RRAM

John F. Hardy II, Jack A. Garrard, Guilherme S.Y. Giardini et al. (+1 more)

This work demonstrates that porous helical WOx architectures enable a distinct low-power regime for planar ITO/WOx/ITO resistive random-access devices. While thin film and helical devices behave similarly at a 5 mA compliance, only helical devices sustain reproducible operation at 500 uA, where RESET voltages reduce by ~60%, switching currents decrease by 68-75%, and SET/RESET power drops by ~89% and ~83%. With helical devices operating at 500 uA, the memory window expands 400-600% due to selective suppression of high-resistive-state leakage, yielding both lower-power and improved read margin in a regime inaccessible to thin film devices. These results highlight geometry-driven field enhancement and confinement as practical design principles for low-power, high-margin resistive memories and point toward opportunities in transparent, flexible, and high-surface-area material systems.
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All authors John F. Hardy II, Jack A. Garrard, Guilherme S.Y. Giardini, Carlo R. daCunha

Materials Science

Incorporating Si into Sb2Se3: Tailoring Optical Phase Change Materials via Nanocomposites

Chih-Yu Lee, Yi-Siou Huang, Felix Adams et al. (+10 more)

Chalcogenide-based optical phase change materials (OPCMs) exhibit a large contrast in refractive index when reversibly switched between their stable amorphous and crystalline states. OPCMs have rapidly gained attention due to their versatility as nonvolatile amplitude or phase modulators in various photonic devices. However, open challenges remain, such as achieving reliable response and transparency spanning into the visible spectrum, a combination of properties in which current broadband OPCMs (e.g., Ge2Sb2Se4Te1, Sb2Se3, or Sb2S3) fall short. Discovering novel materials or engineering existing ones is, therefore, crucial in extending the application scope of OPCMs. Here, we use magnetron co-sputtering to study the effects of Si doping into Sb2Se3. We employ ellipsometry, X-ray diffraction, Raman spectroscopy, and scanning and transmission electron microscopy to investigate the effects of Si doping on the optical properties and crystal structure and compare these results with those from first principles calculations. Moreover, we study the crystallization and melt-quenching of thin films via nano-differential scanning calorimetry (NanoDSC). Our experiments demonstrate that 20% Si doping increases the transparency window in both states, specifically to 800 nm (1.55 eV) in the amorphous phase, while reducing power consumption by lowering the melting temperature. However, this reduction comes at the cost of reducing the refractive index contrast between states and slowing the kinetics of the phase transition.
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All authors Chih-Yu Lee, Yi-Siou Huang, Felix Adams, Chuanyu Lian, Hongyi Sun, Jie Zhao, Zichao Ye, Nathan Youngblood, Juejun Hu, Leslie H Allen, Yifei Mo, Ichiro Takeuchi, Carlos A Rios Ocampo

Materials Science · Cross-listed from cs.LG

High Cycle S-N curve prediction for Al 7075-T6 alloy using Recurrent Neural Networks (RNNs)

Aryan Patel

Aluminum is a widely used alloy, which is susceptible to fatigue failure. Characterizing fatigue performance for materials is extremely time and cost demanding, especially for high cycle data. To help mitigate this, a transfer learning based framework has been developed using Long short-term memory networks (LSTMs) in which a source LSTM model is trained based on pure axial fatigue data for Aluminum 7075-T6 alloy which is then transferred to predict high cycle torsional S-N curves. The framework was able to accurately predict Al torsional S-N curves for a much higher cycle range. It is the belief that this framework will help to drastically mitigate the cost of gathering fatigue characteristics for different materials and help prioritize tests with better cost and time constraints.
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Materials Science · Cross-listed from cond-mat.mes-hall

Electron-beam-induced Contactless Manipulation of Interlayer Twist in van der Waals Heterostructures

Nicola Curreli, Tero S. Kulmala, Riya Sebait et al. (+6 more)

The ability to dynamically control the relative orientation of layers in two dimensional (2D) van der Waals (vdW) heterostructures represents a critical step toward the realization of reconfigurable nanoscale devices. Existing actuation methods often rely on mechanical contact, complex architectures, or extreme operating conditions, which limit their applicability and scalability. In this work, we present a proof-of-concept demonstration of contactless electrostatic actuation based on electron-beam-induced charge injection. By locally charging an insulating hexagonal boron nitride (hBN) flake on an electrically grounded graphene layer, we create an interfacial electric field that generates in-plane electrostatic torque and induces angular displacement. We validate the induced rotation through in-situ scanning electron microscopy (SEM) and twist-dependent Raman spectroscopy.
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All authors Nicola Curreli, Tero S. Kulmala, Riya Sebait, Nicolò Petrini, Matteo Bruno Lodi, Roman Furrer, Alessandro Fanti, Michel Calame, Ilka Kriegel

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

Assessing the impact of contact time on leachate chemistry from recycled concrete aggregates

Morgan D. Sanger, Gabrielle Campagnola, Robin Ritchey et al. (+2 more)

Recycled concrete aggregate (RCA) is recognized as a readily available, mechanically sufficient construction and demolition waste product that is suitable as a base course substitute for natural, virgin aggregate in pavement construction. Environmentally responsible applications of RCA must consider the high alkalinity, high pH leachate, and heavy metal leaching risks reported in the literature. The existing body of literature does not address discrepancies between field and laboratory measurements of RCA leachate pH, nor are there any existing studies of aged RCA leachate composition as a function of time. To consider the influence of contact time on RCA leachate, the present study evaluates recovered RCA base course samples from the Minnesota Road Research highway construction study site using modified batch test methodology. Leachate pH, alkalinity, and calcium ion (Ca2+) concentration were monitored for 24 hours to understand RCA leachate chemistry during the initial contact period. Leachate pH is high upon initial contact with water (pH > 10) and decreases over time as it reacts with atmospheric carbon dioxide. Calcium ion concentration increases rapidly in the initial contact period, then more gradually as calcium saturation is reached. Alkalinity stabilizes (50-65 mg CaCO3/L) after a dramatic increase during the initial contact period.
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All authors Morgan D. Sanger, Gabrielle Campagnola, Robin Ritchey, Tuncer B. Edil, Matthew Ginder-Vogel

Materials Science

Improper-proper ferroelectric competition as a mechanism for multistate polarisation and ferrielectric-like behaviour

Cameron A.M Scott, Finlay D. Morrison and Nicholas. C. Bristowe

In this paper, we re-explore a simple textbook Landau model describing improper ferroelectricity and show that in the limit where both proper and improper instabilities exist and compete, improper ferroelectrics can display switching between multiple polarisation states. Using first principles calculations we highlight how the hexagonal tungsten bronze materials may be an archetypal case, with the possibility to switch between improper and proper phases. The resulting functional characteristics are akin to "ferrielectrics", with switching behaviour in the form of a triple hysteresis loop. Such functionality could be ideal for creating non-volatile multistate systems for use in memory devices or as a backbone for neuromorphic computing.
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Materials Science

The line bundle regime and the scale-dependence of continuum dislocation dynamics

Joseph Pierre Anderson and Anter El-Azab

Continuum dislocation dynamics (CDD) has become the state-of-the-art theoretical approach for mesoscale dislocation plasticity of metals. Within this approach, there are multiple CDD theories that can all be derived from the principles of statistical mechanics. In these theories density-based measures are used to represent dislocation lines. Establishing these density measures requires some level of coarse graining with the result of losing track of some parts of the dislocation population due to cancellation in the tangent vectors of unaligned dislocations. The leading CDD theories either treat dislocations as nearly parallel or distributed locally over orientation space. The difference between these theories is a matter of the spatial resolution at which the definition of the relevant dislocation density field holds: for fine resolutions, single dislocations are resolved and there is no cancellation; for coarse resolutions, whole dislocation loops could contribute at a single point and there is complete cancellation. In the current work, a formulation of the resolution-dependent transition between these limits is presented in terms of the statistics of dislocation line orientation fluctuations about a local average line direction. From this formulation, a study of the orientation fluctuation behavior in intermediate resolution regimes is conducted. Two possible closure equations for truncating the moment sequence of the fluctuation distributions relating the two theories mentioned above are evaluated from data, the newly introduced line bundle closure and the previous standard maximum entropy closure relations. The line bundle closure relation is shown to be accurate for coarse-graining lengths up to half the dislocation spacing and the maximum entropy closure is found to poorly agree with the data at all coarse-graining lengths.
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Materials Science · Cross-listed from quant-ph

Quantum simulation of carbon capture in periodic metal-organic frameworks

Dario Rocca, Jerome F. Gonthier, Joshua Levin et al. (+4 more)

Carbon capture is vital for decarbonizing heavy industries such as steel and chemicals. Metal-organic frameworks (MOFs), with their high surface area and structural tunability, are promising materials for CO2 capture. This study focuses on Fe-MOF-74, a magnetic Mott insulator with exposed metal sites that enhance CO2 adsorption. Its strongly correlated electronic structure challenges standard DFT methods, which often yield inconsistent predictions. We initially benchmark adsorption energies using various DFT functionals, revealing substantial variability and underscoring the need for more accurate approaches, such as those provided by quantum computing. However, practical quantum algorithms are far less established for simulations of periodic materials, particularly when the plane-wave basis set, often comprising tens of thousands of basis vectors, is used. To address this, we employ an active space reduction strategy based on Wannier functions and natural orbital selection. Localized orbitals around the adsorption site are identified, and MP2 natural orbitals are used to improve convergence of correlation energies. Adsorption energies are then computed using a quantum number-preserving ansatz within the variational quantum eigensolver framework. In addition to classical simulations, we conduct quantum experiments using the sample-based quantum diagonalization method. Although current hardware limits the size of feasible simulations, our approach offers a more efficient and scalable path forward. These results advance the applicability of quantum algorithms to realistic models of carbon capture and periodic materials more broadly.
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All authors Dario Rocca, Jerome F. Gonthier, Joshua Levin, Tobias Schafer, Andreas Gruneis, Byeol Kang, Hong Woo Lee