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Physics Condensed Matter Materials Science

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Wednesday 12 November

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

Interface tuned Enhanced and Low Temperature Quenching of Orbital Hall Currents Induce Torque and magnetoresistance in Light Metal/Nickel Bilayers

Dhananjaya Mahapatra, Harekrishna Bhunia, Manu S Pattelath et al. (+1 more)

We investigate orbital current induced effects arising from the orbital Hall effect in light-metal/ferromagnet bilayers. Thin films of Ti in ohmic contact with Ni were studied using second-harmonic longitudinal and transverse voltage measurements under an applied a.c. current. From these signals, we extract the orbital Hall torque (OHT) efficiency and the unidirectional orbital magnetoresistance (UOMR). Insertion of a Cu interlayer between the Ni/Ti interface leads to an enhancement of both OHT efficiency and UOMR compared to both Ni/Ti and Ni/Cu bilayers. Furthermore, systematic variation of Ti thickness reveals that both OHT efficiency and UOMR increase with increasing Ti thickness, indicating that the observed phenomena predominantly originate from the bulk orbital Hall effect rather than purely from interfacial mechanisms and Lowering the temperature leads to a clear reduction in both the orbital Hall torque (OHT) efficiency and the unidirectional orbital magnetoresistance (UOMR). The nearly linear and correlated temperature dependence of both parameters suggests a common underlying mechanism, namely, the orbital Hall effect in the light-metal layer, which governs both the generation of orbital current and its subsequent influence on the ferromagnet through orbital torque and orbital magnetoresistance.
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All authors Dhananjaya Mahapatra, Harekrishna Bhunia, Manu S Pattelath, Partha Mitra

Materials Science

Low-Temperature Heat Capacity and Phonon Dynamics in Expanded Graphite and EG–MWCNTs Composites

A.I. Krivchikov, A. Jeżowski, M.S. Barabashko et al. (+11 more)

The specific heat of expanded graphite (EG) and EG–multiwalled carbon nanotube (MWCNT) composites (1.0 and 3.0 wt.% MWCNTs) was measured between 2 and 300~K. The low-temperature heat capacity is dominated by out-of-plane flexural phonons with quadratic dispersion, characteristic of two-dimensional layered systems. Compared with crystalline graphite, EG exhibits enhanced heat capacity due to increased defect density and reduced interlayer coupling. Structural characterization (XRD, Raman, EDS) confirmed variations in stacking order and defect concentration. The data were fitted using a three-term model ($C_{1}T + C_{3}T^{3} + C_{5}T^{5}$), where the negative $C_{5}$ term indicates quadratic phonon dispersion. The results demonstrate the influence of MWCNT integration and structural disorder on phonon dynamics and anisotropic heat capacity in EG-based composites.
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All authors A.I. Krivchikov, A. Jeżowski, M.S. Barabashko, G. Dovbeshko, D.E. Hurova, N.N. Galtsov, V. Boiko, Yu. Sementsov, A. Glamazda, V. Sagan, Yu. Horbatenko, O.A. Korolyuk, O.O. Romantsova, D. Szewczyk

Materials Science

Laser-generated GHz surface acoustic waves with tunable amplitude during the magnetostructural phase transition in FeRh thin films

Ia. A. Mogunov, A. Yu. Klokov, N. Yu. Frolov et al. (+6 more)

Laser-generated surface acoustic waves (SAW) facilitate efficient information processing in modern spintronics and magnonics. The ability to tune the SAW parameters such as amplitude is crucial to achieve acoustic control over magnonic properties. Such tunability can be achieved in phasechanging magnetic materials that accommodate both spin waves and SAWs. A promising material is the FeRh alloy, a metallic antiferromagnet at room temperature that undergoes a phase transition to the ferromagnetic state accompanied by a crystal lattice expansion at 370 K. This transition can also be induced by femtosecond laser pulses. In this paper, we use the phase transition in a 60 nm Fe49Rh51 film to optically generate pulses of Gigahertz quasi-Rayleigh SAWs. We detect them via the photoelastic effect and show that the lattice transformation during the phase transition is a dominant strain-generation mechanism for above-threshold excitation. The weight of this contribution rises as the sample is heated closer to the AFM-FM transition temperature and 'switches off' when heated above it, allowing for control of the SAW amplitude. A model based on thermodynamic parameters of Fe49Rh51 shows that the lattice transformation occurring within 95 ps effectively contributes to SAW generation happening on a comparable timescale, while non-equilibrium fast kinetics of the phase transition does not.
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All authors Ia. A. Mogunov, A. Yu. Klokov, N. Yu. Frolov, A. V. Protasov, G. E. Zhezlyaev, D. I. Devyaterikov, R. R. Gimaev, V. I. Zverev, A. M. Kalashnikova

Materials Science

Hydrogen permeability prediction in palladium alloys and virtual screening of B2-phase stabilized Pd(100-x-y)CuxMy ternary alloys using machine learning

Eric Kolor, Edoardo Magnone, Muhammad Harussani Moklis et al. (+4 more)

We present a forward prediction material screening framework designed to discover Pd-Cu alloys with improved B2 phase stability, thereby unlocking simultaneous $H_2$ generation and utilization. First, we trained CatBoost models with literature-derived Pd alloy data to predict $H_2$ permeability from composition and testing conditions. We evaluated fractional, composition-based, and physics-informed descriptors, individually and in combination, and showed that sequential Pearson filtering and fold-wise SHAP-based recursive feature elimination with cross-fold aggregation reduced errors while controlling complexity. Guided by the one-SE rule, a narrower domain-informed set of 13 features provided the best accuracy parsimony trade-off ($R^2=0.81$), only 0.01 below the max. $R^2$ achievable with 3x the number of features. SHAP analysis indicated that high permeability is promoted by elevated temperature, lattice expansion relative to Pd, atomic size mismatch, and favorable mixing tendencies. Second, the selected model was applied to screen $Pd_{(100-x-y)}Cu_{x}M_{y}$ spanning 16 co-dopants M for B2 stabilization. For each M system, we obtained the Pareto set of compositions that minimize Pd content and Miedema heat of formation and maximize the permeability, then picked three compounds, including that with the highest predicted permeability, the lowest Miedema heat of formation, and the lowest Pd content. With a final filter considering M concentration for single-phase Pd-M solution formation, we recommend Pd48.48Cu43.00Y8.52, Pd49.08Cu42.45Sc8.47, Pd56.09Cu33.70La10.21, and Pd52.68Cu40.44Mg6.88 for experimental validation. We predict those alloys to exhibit permeabilities 1.7 to 1.9 higher than B2 Pd60Cu40. Our framework provides plausible experimental targets and a scalable pathway for designing stable, high-temperature, H2-selective Pd-alloy membranes.
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All authors Eric Kolor, Edoardo Magnone, Muhammad Harussani Moklis, Md. Rubel, Sasipa Boonyubol, Koichi Mikami, Jeffrey S. Cross

Materials Science

Phase transformations in metastable $\beta$ Zr15Nb alloy revealed by in-situ methods

Anna Veverková, Kristína Bartha, Jozef Veselý et al. (+6 more)

This study examines the phase transitions occurring during linear heating of the Zr15Nb alloy through a comprehensive, multi-technique methodology comprising in-situ high-energy synchrotron X-ray diffraction (HEXRD), electrical resistance measurements, differential scanning calorimetry (DSC), and thermal expansion analysis, supplemented by ex-situ transmission electron microscopy (TEM). The findings reveal a complex sequence of phase transformations and corresponding structural changes over a broad temperature range (from room temperature up to 800 ${\deg}$C). Two distinct body-centered cubic (bcc) $\beta$ phases - $\beta_{Zr}$ and $\beta_{Nb}$ - with closely related lattice parameters are identified. At room temperature, the microstructure is characterized by a mixture of the metastable $\beta_{Zr}$ + $\omega_{ath}$ phase. Upon heating, $\beta_{Zr}$ progressively decomposes, giving rise to the formation of $\beta_{Nb}$. TEM observation revealed the cuboidal shape of the $\omega_{iso}$ particles resulting from the high lattice misfit between $\beta$ and $\omega$ phase. The $\omega$ solvus temperature is determined to be approximately 555 ${\deg}$C, as evidenced by in situ HEXRD and abrupt changes in the alloy's thermal and electrical properties. The growth of the $\alpha$ phase occurs after the dissolution of the $\omega$ phase, resulting in a pronounced increase in thermal expansion.
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All authors Anna Veverková, Kristína Bartha, Jozef Veselý, Pere Barriobero-Vila, Jiří Kozlík, Petr Doležal, Jiří Pospíšil, Jana Šmilauerová, Josef Stráský

Materials Science

Assessing Band Gap Stability of Organic Semiconductor Thin Films for Flexible Electronic Applications

Mahya Ghorab, Ayush K. Ranga, Arnulf Materny et al. (+2 more)

Integration of organic semiconductors into flexible electronics requires that their optoelectronic properties remain stable under mechanical deformation. Among these, the optical band gap governs exciton generation and limits photovoltaic voltage, making it a key parameter for strain-resilient design. In this work, we investigate band gap shifts in poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/P3HT thin films deposited on flexible poly(ethylene terephthalate) (PET) substrates under uniaxial tensile strain ranging from 1% to 10%. Samples were subjected to mechanical deformation and then characterized by ultraviolet–visible (UV–Vis) absorption spectroscopy. The optical band gaps extracted using a standardized Tauc analysis and statistically validated through equivalence testing and robust regression models. We find that up to 7% strain, the band gap shift ($\Delta E_g$) remains effectively invariant, independent of annealing condition or stack configuration, demonstrating electronic stability. However, at 10% strain, all groups exhibit a reproducible widening of $\sim$4–5~meV. This threshold-like behavior marks a transition from mechanical accommodation to electronic perturbation. These findings confirm that the optical band gap in semicrystalline P3HT-based thin films is robust under practical deformation, which provides clear strain thresholds to inform mechanical modeling and device-level simulation of flexible organic optoelectronic systems.
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All authors Mahya Ghorab, Ayush K. Ranga, Arnulf Materny, Veit Wagner, Mojtaba Joodaki

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

First-principles evidence for conventional superconductivity in a quasicrystal approximant

Pedro N. Ferreira, Roman Lucrezi, Sangmin Lee et al. (+7 more)

Quasicrystals (QCs) host long-range order without translational symmetry, a regime in which the very foundations of BCS theory are not straightforwardly applicable, yet experiments on QCs and their approximant crystals (ACs) point to conventional, $s$-wave, electron-phonon coupled superconductivity. Here we test the predictive power of the electron-phonon framework in a representative decagonal AC from first principles. Using state-of-the-art ab initio methods, we compute the superconducting properties of the recently discovered AC Al$_{13}$Os$_4$ and quantitatively reproduce its bulk $T_\text{c}$. This constitutes, to our knowledge, the first ab initio determination of $T_\text{c}$ for an AC and establishes that the electron-phonon framework is predictive in these systems as well. Using the generalized quasichemical approximation for alloy modeling in the decagonal Al–Os family, we predict tunable superconductivity in Al$_{13}$Os$_{4-x}$Re$_x$ and Al$_{13}$Os$_{4-x}$Ir$_x$; in particular, Al$_{13}$Re$_4$ is dynamically stable and estimated to have a $T_\text{c}$ about 30% above Al$_{13}$Os$_4$. Finally, we discuss the role of ACs as high-fidelity proxies for their parent QCs. Although long-range quasiperiodicity may introduce subtle electronic features, our findings indicate that the key ingredients for superconductivity are already encoded in the local structural motifs preserved by the AC. This places the Al–Os and Al–Re families among the most promising candidates for the highest-$T_\text{c}$ quasicrystalline superconductivity.
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All authors Pedro N. Ferreira, Roman Lucrezi, Sangmin Lee, Lucy Nathwani, Matthew Julian, Rohit P. Prasankumar, Warren E. Pickett, Chris J. Pickard, Philip Kim, Christoph Heil

Materials Science

Enhanced spectral range of strain-induced tuning of quantum dots in circular Bragg grating cavities

Ivan Gamov, Matthias Sauter, Samuel Huber et al. (+5 more)

Tunable sources of entangled and single photons are essential for implementing entanglement-based quantum information protocols, as quantum teleportation and entanglement swapping depend on photon indistinguishability. Tunable devices are fabricated from indium arsenide (InAs) quantum dots (QDs) embedded in gallium arsenide (GaAs) nanomembranes placed on monolithic piezoelectric substrates. Circular Bragg grating (CBG) resonators enhance emission brightness and exploit the Purcell effect; however, the inclusion of CBGs reduces strain-mediated tunability compared to planar nanomembranes. A simple and effective solution is introduced: filling the CBG trenches with a stiff dielectric (aluminum oxide) via atomic layer deposition (ALD) restores up to 95% of the tunability of planar structures. Finite element analysis (FEA) confirms that the tunability loss originates from bending in the device layers due to strain relief in the CBG geometry. Lowering the stiffness of intermediate layers between the QDs and the piezoelectric actuator, such as in bonding or reflector layers, further increases strain losses in uncoated CBGs. Coated devices maintain 98-99% strain-tuning efficiency across all simulated underlayer stiffnesses. The results demonstrate that advantageous optical cavity properties can be effectively combined with piezoelectric strain tuning, enabling scalable, bright, and tunable quantum light sources.
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All authors Ivan Gamov, Matthias Sauter, Samuel Huber, Quirin Buchinger, Peter Gschwandtner, Ulrike Wallrabe, Sven Höfling, Tobias Huber-Loyola

Materials Science

Discovery of a new magnesium iron boride Mg4Fe1.1B13.9 in the Mg-Fe-B-N system

N.D. Zhigadlo

A new boron-rich ternary phase, Mg4Fe1.1B13.9, was discovered in the Mg-Fe-B-N quaternary system. This novel phase appears in the form of plate-like shaped crystals formed on the surface of Fe-substituted MgB2 during high-pressure, high-temperature (HPHT) solution growth at 3 GPa and 1960 C. Mg4Fe1.1B13.9 crystallizes in an orthorhombic structure with space group Pnam (No. 62) and lattice parameters a = 10.95(2) A, b = 7.07(1) A, and c = 8.72(1) A. Structural refinement reveals a layered architecture composed of alternating layers of Mg-Fe and boron, with boron atoms forming 5-, 6-, and 7-membered ring motifs. A structural comparison indicates that Mg4Fe1.1B13.9 is closely related to the Y2ReB6-type borides. This discovery highlights the effectiveness of the HPHT synthesis in accessing new, complex boron-rich phases. As research in the binary Mg-B system approaches saturation, the identification of Mg4Fe1.1B13.9 offers new insights into the formation of phases in the Mg-Fe-B-N system. This paves the way for the guided synthesis of novel borides with unique properties in other multicomponent systems.
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Materials Science

High-throughput, Non-Destructive, Three-Dimensional Imaging of GaN Threading Dislocations with in-Plane Burgers Vector Component via Phase-Contrast Microscopy

Yukari Ishiakwa, Ryo Hattori, Yongzhao Yao et al. (+2 more)

We demonstrate a nondestructive, high-throughput method for observing dislocations in GaN (0001) using phase-contrast microscopy (PCM). The PCM images (359x300 $\mu$m$^2$) analyzed in this study were acquired with an exposure time of 3 ms per image. The one-to-one correspondence between threading dislocation (TD) contrasts in PCM images and the corresponding contrasts in multiphoton excitation photoluminescence (MPPL) images provides clear evidence that PCM can detect TDs with in-plane Burgers vector components. The contrast shape in PCM reflects the inclination of dislocations with respect to the surface normal: dot contrasts correspond to vertical dislocations, whereas line contrasts correspond to inclined dislocations. By shifting the focal plane from the top surface to the back surface, the three-dimensional propagation paths of dislocations can be visualized. The PCM image obtained represents a projection of threading dislocations within a thickness of approximately 43 $\mu$m. Dislocations spaced as close as 1.3 $\mu$m can be individually resolved. In addition, the capability of PCM to detect scratches, subsurface scratches, facet boundaries, and voids was demonstrated. This study establishes PCM as a versatile and laboratory-accessible technique for three-dimensional, nondestructive characterization of dislocations and other defects in wide-bandgap semiconductors.
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All authors Yukari Ishiakwa, Ryo Hattori, Yongzhao Yao, Daiki Katsube, Koji Sato

Materials Science

High-speed, High-Resolution, Three-Dimensional Imaging of Threading Dislocations in beta-$Ga_{2}O_{3}$ via Phase-Contrast Microscopy

Yukari Ishiakwa, Daiki Katsube, Yongzhao Yao et al. (+2 more)

This study presents a nondestructive, high-resolution method for three-dimensional imaging of threading dislocations in beta-$Ga_{2}O_{3}$ (010) using phase-contrast microscopy (PCM). A one-to-one correspondence between dislocation contrasts in PCM images and synchrotron X-ray topography (SR-XRT) images confirms the detection capability of PCM. Compared to SR-XRT, PCM provides enhanced spatial resolution, enabling the distinction of closely spaced dislocations with sub-10-micrometer separation. PCM facilitates direct visualization of dislocation propagation paths along the depth (z) direction by systematically shifting the focal plane into the crystal. In addition, the projection of stacked PCM images enables in-plane (XY) tracing of dislocation lines, providing insight into the preferred slip systems in beta-$Ga_{2}O_{3}$. This work establishes PCM as a versatile and laboratory-accessible technique for three-dimensional, nondestructive characterization of dislocations across entire wide-bandgap semiconductor wafers within a practically acceptable time frame.
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All authors Yukari Ishiakwa, Daiki Katsube, Yongzhao Yao, Koji Sato, Kohei Sasaki

Materials Science

AC magnetometry of van der Waals magnets using ultrasensitive Graphene Hall sensors

Eugene Park, Jihoon Keum, Ji-Hwan Baek et al. (+5 more)

Probing the dynamical magnetic properties of two-dimensional (2D) materials requires sensitive techniques capable of detecting small magnetic fields from nanoscale samples. We demonstrate quantitative AC and DC magnetometry of a ferromagnetic Fe3-xGeTe2 nanoflakes using ultrasensitive graphene Hall sensors. These devices achieve record-low magnetic field detection noise at both cryogenic and room temperature, enabled by hBN encapsulation, low-resistance fluorographene contacts, and a novel fabrication process. We perform quantitative AC susceptibility measurements up to 1 kHz, resolving both real and imaginary components with nanotesla-scale sensitivity and milliradian phase accuracy, the first such measurement in a van der Waals magnet. Our results establish graphene Hall sensors as a powerful and broadly applicable platform for studying magnetic and superconducting phases near the 2D limit.
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All authors Eugene Park, Jihoon Keum, Ji-Hwan Baek, Hyuncheol Kim, Kenji Watanabe, Takashi Taniguchi, Gwan-Hyoung Lee, Je-Geun Park

Materials Science

MicroEvoEval: A Systematic Evaluation Framework for Image-Based Microstructure Evolution Prediction

Qinyi Zhang, Duanyu Feng, Ronghui Han et al. (+2 more)

Simulating microstructure evolution (MicroEvo) is vital for materials design but demands high numerical accuracy, efficiency, and physical fidelity. Although recent studies on deep learning (DL) offer a promising alternative to traditional solvers, the field lacks standardized benchmarks. Existing studies are flawed due to a lack of comparing specialized MicroEvo DL models with state-of-the-art spatio-temporal architectures, an overemphasis on numerical accuracy over physical fidelity, and a failure to analyze error propagation over time. To address these gaps, we introduce MicroEvoEval, the first comprehensive benchmark for image-based microstructure evolution prediction. We evaluate 14 models, encompassing both domain-specific and general-purpose architectures, across four representative MicroEvo tasks with datasets specifically structured for both short- and long-term assessment. Our multi-faceted evaluation framework goes beyond numerical accuracy and computational cost, incorporating a curated set of structure-preserving metrics to assess physical fidelity. Our extensive evaluations yield several key insights. Notably, we find that modern architectures (e.g., VMamba), not only achieve superior long-term stability and physical fidelity but also operate with an order-of-magnitude greater computational efficiency. The results highlight the necessity of holistic evaluation and identify these modern architectures as a highly promising direction for developing efficient and reliable surrogate models in data-driven materials science.
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All authors Qinyi Zhang, Duanyu Feng, Ronghui Han, Yangshuai Wang, Hao Wang

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

Phonon Thermal Hall Effect: The Roles of Disorder, Annealing, and Metallic Contacts

Qiaochao Xiang, Xiaokang Li, Xiaodong Guo et al. (+2 more)

The phonon thermal Hall effect (THE) is a ubiquitous yet poorly understood phenomenon in insulators. Its microscopic origin remains debated, partly due to significant sample-dependent variations that hint at uncontrolled experimental parameters. Using SrTiO$_3$ as a model system, we identify disorder and uncontrolled strain as suppressors of a thermal Hall signal. Crystals with high thermal conductivity exhibit a substantial thermal Hall angle $\nabla T_y / \nabla T_x$ (up to 0.3% at 9 T), whereas the effect is virtually absent in disordered samples. Crucially, annealing (in air atmosphere) these disordered samples partially restores the THE (approximately 0.1% at 9 T) with little effect on the longitudinal thermal conductivity. This decoupling reveals that the amplitude of THE is not simply set by the phonon mean free path. Furthermore, measurements performed with metallic and insulating contacts yield identical results on the same sample. This definitively rules out parasitic signals as the effect's origin. Our work, by establishing the phonon THE as an intrinsic property of the crystal lattice and extremely sensitive to disorder, sharply constrains theoretical scenarios.
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All authors Qiaochao Xiang, Xiaokang Li, Xiaodong Guo, Kamran Behnia, Zengwei Zhu

Materials Science

Quasi-linear magnetoresistance and paramagnetic singularity in Hypervalent Bismuthide

Zhongchen Xu, Yi Yan, Zhihao Liu et al. (+7 more)

Materials featuring hypervalent bismuth motifs have generated immense interest due to their extraordinary electronic structure and exotic quantum transport. In this study, we synthesized high-quality single crystals of La3ScBi5 characterized by one-dimensional hypervalent bismuth chains and performed a systematic investigation of the magnetoresistive behavior and quantum oscillations. The metallic La3ScBi5 exhibits a low-temperature plateau of electrical resistivity and quasi-linear positive magnetoresistance, with anisotropic magnetoresistive behaviors suggesting the presence of anisotropic Fermi surfaces. This distinctive transport phenomenon is perfectly elucidated by first-principles calculations utilizing the semiclassical Boltzmann transport theory. Furthermore, the nonlinear Hall resistivity pointed towards a multiband electronic structure, characterized by the coexistence of electron and hole carriers, which is further supported by our first-principles calculations. Angle-dependent de Haas-van Alphen oscillations are crucial for further elucidating its Fermiology and topological characteristics. Intriguingly, magnetization measurements unveiled a notable paramagnetic singularity at low fields, which might suggest the nontrivial nature of the surface states. Our findings underscore the interplay between transport phenomena and the unique electronic structure of hypervalent bismuthide La3ScBi5, opening avenues for exploring novel electronic applications.
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All authors Zhongchen Xu, Yi Yan, Zhihao Liu, Jie Pang, Guohao Dong, Xiutong Deng, Shengnan Zhang, Xianmin Zhang, Youguo Shi, Quansheng Wu

Materials Science

Mobile chemical cage: Revealing the origin of anomalous lithium diffusion in liquid $Li_{17}Pb_{83}$ alloy

Sensen Lin, Yang Gao, Yongheng Lu et al. (+2 more)

The high-temperature performance of liquid $Li_{17}Pb_{83}$, a key fusion reactor material, is governed by its atomic-scale dynamics. Using ab initio molecular dynamics, we discover that lithium diffusion is not free but confined within cages formed by lead atoms, a phenomenon we term the chemical cage effect. Structurally, RDF and CSRO analyses confirm a stable local environment where Li is preferentially surrounded by Pb. Dynamically, the MSD and NGP reveal anomalous, heterogeneous lithium diffusion characterized by repeated cage-breaking events. The double-exponential relaxation of the Li-Pb bond probability further distinguishes the escape dynamics of Li from surface and bulk cages. ELF and DOS analyses identify the polar covalent Li-Pb bond as the electronic origin of this cage. This study establishes the chemical bond-directed synergistic cage effect as the core mechanism in $Li_{17}Pb_{83}$, moving beyond traditional geometric constraint models and providing a new paradigm to understand transport in multi-component liquid alloys.
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All authors Sensen Lin, Yang Gao, Yongheng Lu, Yongkuan Zhang, Yiqiang Sun

Tuesday 11 November

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

Nanobubble size controls gas hydrate nucleation in supercooled water

Ramkhelavan Kanaujiya, Atanu K. Metya, Rajnish Kumar et al. (+1 more)

Gas hydrates are crystalline compounds formed when water molecules encapsulate guest gas molecules under high pressure and low temperatures. They have gained significant interest due to their potential as alternative energy resources and their applications in gas storage, transportation, and carbon sequestration. However, the fundamental mechanisms governing their formation, especially the influence of gas bubbles, remain poorly understood. In this study, we use molecular dynamics (MD) simulations to examine how methane nanobubble size modulates hydrate formation in supercooled water. Nanobubbles of different sizes are generated by modulating the methane concentration in a methane-water mixture during equilibration under high-temperature and low-pressure conditions, followed by quenching to low temperature and high pressure to induce gas hydrate nucleation and subsequent growth. The simulations reveal a strong correlation between nanobubble size and the extent of hydrate formation. Specifically, the extent of hydrate formation increases with bubble size in the small-to-intermediate regime. However, beyond a critical bubble size threshold, the hydrate formation efficiency declines. The work provides new molecular-level insight into how nanobubble size modulates gas hydrate nucleation and growth dynamics.
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All authors Ramkhelavan Kanaujiya, Atanu K. Metya, Rajnish Kumar, Tarak K Patra

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

Material-Based Intelligence: Self-organizing, Autonomous and Adaptive Cognition Embodied in Physical Substrates

Vladimir A. Baulin, Rudolf M. Füchslin, Achille Giacometti et al. (+2 more)

The design of intelligent materials often draws parallels with the complex adaptive behaviors of biological organisms, where robust functionality stems from sophisticated hierarchical organization and emergent long-distance coordination among a myriad local components. Current synthetic materials, despite integrating advanced sensors and actuators, predominantly demonstrate only simple, pre-programmed stimulus-response functionalities, falling short of robustly autonomous intelligent behavior. These systems typically execute tasks determined by rigid design or external control, fundamentally lacking the intricate internal feedback loops, dynamic adaptation, self-generated learning, and genuine self-determination characteristic of biological agents. This perspective proposes a fundamentally different approach focusing on architectures where material-based intelligence is not pre-designed, but arises spontaneously from self-organization harnessing far-from-equilibrium dynamics. This work explores interdisciplinary concepts from material physics, chemistry, biology, and computation, identifying concrete pathways toward developing materials that not only react, but actively perceive, adapt, learn, self-correct, and potentially self-construct, moving beyond biomimicry to cultivate fully synthetic, self-evolving systems without external control. This framework outlines the fundamental requirements for, and constraints upon, future architectures where complex, goal-directed functionalities emerge synergistically from integrated local processes, distinguishing material-based intelligence from traditional hardware-software divisions. This demands that concepts of high-level goals and robust, replicable memory mechanisms are encoded and enacted through the material's inherent dynamics, inherently blurring the distinction between system output and process.
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All authors Vladimir A. Baulin, Rudolf M. Füchslin, Achille Giacometti, Helmut Hauser, Marco Werner

Materials Science

TEM Agent: enhancing transmission electron microscopy (TEM) with modern AI tools

Morgan K. Wall, Alexander J. Pattison, Edward S. Barnard et al. (+2 more)

Recent improvements in large language models (LLMs) have had a dramatic effect on capabilities and productivity across many disciplines involving critical thinking and writing. The development of the model context protocol (MCP) provides a way to extend the power of LLMs to a specific set of tasks or scientific equipment with help from curated tools and resources. Here, we describe a framework called TEM Agent designed for transmission electron microscopy (TEM) that leverages the benefits of LLMs through a MCP approach. We simultaneously access and control several subsystems of the TEM, a data management platform, and high performance computing resources through text-based instructions. We demonstrate the abilities of the TEM Agent to set up and complete intricate workflows using a simplified set of MCP tools and resources accompanying a commercial LLM without any additional training. The use of a framework such as the TEM Agent simplifies access to complex microscope ecosystems comprised of several vendor and custom systems enhancing the ability of users to accomplish microscopy experiments across a range of difficulty levels.
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All authors Morgan K. Wall, Alexander J. Pattison, Edward S. Barnard, Stephanie M. Ribet, Peter Ercius

Materials Science

Average density of Bloch electrons in a homogeneous magnetic field: A second-order response

Benjamin M. Fregoso

We compute the average density of a three-dimensional multiband crystal of arbitrary symmetry, metal or insulator, to first and second order in a weak homogeneous magnetic field. To linear order and for insulators, the density follows the well-known Streda formula, but for metals there is an extra contribution from the orbital magnetic moments at the Fermi surface. To second order the average density depends on several microscopic processes. Among these, the quantum metric tensor plays an important role by generating a pseudo-magnetic moment resulting from the rotation of the Bloch wave functions in the complex projective plane. We also discuss the implications of our results for the volume and pressure. The method we develop is explicitly gauge invariant, considers intraband and interband processes on equal footing, accommodates relaxation processes, and can be readily extended to other observables.
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Materials Science · Cross-listed from physics.app-ph

High-Purity Diamond Integration on $\beta$-Ga$_2$O$_3$ via Microwave Plasma CVD for Enhanced Thermal Management

Saleh Ahmed Khan, Stephen Margiotta, Ahmed Ibreljic et al. (+1 more)

The integration of diamond with $\beta$-Ga$_2$O$_3$ presents a promising pathway to enhance thermal management in high-power electronic devices, where the inherently low thermal conductivity of $\beta$-Ga$_2$O$_3$ can lead to localized self-heating and elevated junction temperatures. In this work, we demonstrate a scalable, low-damage approach for integrating polycrystalline diamond films on (010) $\beta$-Ga$_2$O$_3$ substrates via microwave plasma chemical vapor deposition (MPCVD), employing dielectric interlayers and polymer-assisted electrostatic nanodiamond seeding to systematically evaluate the impact of growth conditions on film morphology, grain evolution, phase purity, and optical characteristics. At a growth temperature of 800$^\circ$C, progressive grain coarsening is observed with extended deposition, with the lateral grain size increasing from 37.6 nm (53 nm thickness) to 192.5 nm for an 886 nm-thick film. This microstructural evolution is accompanied by narrowing of the diamond Raman peak and a monotonic increase in the sp$^3$ phase fraction from 95.9% to as high as 98.9%, indicating continued suppression of non-diamond carbon with prolonged growth. Comparison of SiO$_2$ and SiN$_x$ interlayers under identical growth conditions shows only marginal differences in grain size and phase purity, indicating limited interlayer influence once a high nucleation density is established. Importantly, diamond films exhibiting greater than 96% sp$^3$ phase content were achieved at substrate temperatures as low as 480$^\circ$C, highlighting the viability of diamond-on-Ga$_2$O$_3$ integration under reduced thermal budgets. These findings establish a robust and scalable platform for integrating diamond on $\beta$-Ga$_2$O$_3$, supporting the development of next-generation power and RF devices with improved thermal management.
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All authors Saleh Ahmed Khan, Stephen Margiotta, Ahmed Ibreljic, Anhar Bhuiyan

Materials Science

Decoupling Composition and Band Gap in $\kappa$-Ga$_2$O$_3$ Heterostructures via STEM-EELS

Annett Thøgersen, Georg Muntingh, Lasse Vines et al. (+5 more)

High-resolution mapping of electronic properties at oxide heterointerfaces remains challenging due to probe delocalization and overlapping signals. In this work, we employ monochromated, probe-corrected scanning transmission electron microscopy combined with electron energy-loss spectroscopy (STEM-EELS) to resolve band gap variations across $\kappa$-Ga$_2$O$_3$-based multilayers with nanometer-scale precision. A custom automated quantitative-based EELS analysis framework enabled automated band gap fitting and visualization, ensuring reproducibility and high spatial resolution. By optimizing acquisition parameters and quantifying inelastic delocalization, we demonstrate reliable extraction of band gap excitations from layers only a few nanometers thick. For heterostructures grown on ITO templates, strain at defect-free interfaces induces a gradual band gap transition from $5.08~\mathrm{eV}$ to $4.28~\mathrm{eV}$ over $\sim 10~\mathrm{nm}$, despite an abrupt compositional change. In contrast, ZnO-based templates introduce structural defects that relieve strain, yielding band gaps consistent with composition. These results establish STEM-EELS as a powerful tool for nanoscale electronic characterization and highlight the dominant role of interfacial strain over composition in governing local band structure.
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All authors Annett Thøgersen, Georg Muntingh, Lasse Vines, Øystein Prytz, Max Kneiß, Marius Grundmann, Holger von Wenckstern, Ingvild J. T. Jensen

Materials Science

Polaron and Strain Effects on Ion Migration in WO$_3$

Matthäus Siebenhofer, Pjotrs Žguns and Bilge Yildiz

Ion migration in WO$_3$ is a critical process for various technological applications, such as in batteries, electrochromic devices and energy-efficient brain-inspired computing devices. In this study, we investigate the migration mechanisms of H$^+$, Li$^+$, and Mg$^{2+}$ ions in monoclinic WO$_3$, and how energy barriers are affected by the presence of electron polarons and by lattice strain. Our approach in calculating the migration paths and barriers is based on density functional theory methods. The results show that the presence of polarons leads to association effects and lattice deformations that increase ion migration barriers. Therefore, the consideration of polarons is critical to accurately predict activation energies of ion migration. We further show that lattice strain modulates ion migration barriers, however, the impact of strain depends on the migrating ion. For protons that are embedded in the oxygen ion electronic shells and hop from donor to acceptor oxygens, compressive lattice strain accelerates migration by reducing the donor-acceptor distance. In contrast, the migration barriers of larger ions decrease with tensile lattice strain that increases the free space for the ion in the transition state. These insights into the effects of polarons and lattice strain are important for understanding and tuning properties of WO$_3$ when aiming for optimized device characteristics.
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Materials Science

Low-Field Ferroelectricity in 10 nm AlBScN Thin Films

Xiaolei Tong, Pedram Yousefian, Ziyi Wang et al. (+5 more)

Ferroelectric aluminum scandium nitride (Al1-xScxN, AlScN) offers CMOS-compatible integration but suffers from high coercive fields and leakage currents that hinder thickness scaling. Further reduction in thickness is essential for low-voltage embedded nonvolatile memory applications. Boron incorporation into AlScN (AlBScN) suppresses leakage current in films down to 40 nm, yet its ferroelectric characteristics in ultrathin films remains unexplored. This letter demonstrates robust ferroelectric switching in 10 nm sputtered AlBScN capacitors with a low coercive field and approximately two orders of magnitude lower leakage than AlScN. Notably, ferroelectric switching was observed at 2.2 MV/cm in capacitance-voltage measurements, and symmetric polarization reversal occurred near 4.6 MV/cm in positive-up-negative-down (PUND) measurements using 2 {\mu}s pulses. Moreover, Weibull analysis revealed a breakdown-to-coercive-field ratio (EBD/Ec) of ~2.2. These findings demonstrated AlBScN as a promising candidate for CMOS back-end-of-line (BEOL) compatible ferroelectric applications with improved energy consumption and reduced leakage current.
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All authors Xiaolei Tong, Pedram Yousefian, Ziyi Wang, Meenakshi A. Saravanan, Rajeev Kumar Rai, Giovanni Esteves, Eric A. Stach, Roy H. Olsson III

Materials Science

Synergetic Enhancement on Bulk and Grain Boundary Ionic Conduction of Mg Doped High-Entropy NASICON-Type Solid Electrolyte for Solid-State Na+ Batteries by Spray Flame Synthesis

Tianyi Wu, Yiyang Zhang, Zhu Fang et al. (+3 more)

All-solid-state sodium batteries represent a promising next-generation energy storage technology, owing to cost-effectiveness and enhanced safety. Among solid electrolytes for solid-state sodium batteries, NASICON-structured Na3Zr2Si2PO12 has emerged as a predominant candidate. However, its widespread implementation remains limited by suboptimal ionic conductivity in both bulk and grain boundary regions. In this study, we demonstrate a novel approach utilizing swirling spray flame synthesis to produce Mg-doped NASICON solid electrolyte nanoparticles. This method facilitates efficient doping and homogeneous mixing for scalable production, resulting in core-shell non-NASICON structures with nano-scale high-entropy mixing. Notably, the atomic migration distances achieved by flame synthesis are significantly reduced compared to conventional solid-state reactions, thereby enabling reactive sintering to preserve high sinterability of nanoparticles during post-treatment processes. High-temperature sintering yields dense NASICON-structured solid electrolytes. Among those, Mg0.25NZSP exhibits an optimal ionic conductivity of 1.91 mS/cm at room temperature and an activation energy of 0.200 eV. The enhancement mechanism can be attributed to incorporation into the NASICON phase and formation of a secondary phase. The low-melting-point secondary phase significantly improves grain boundary contact to enhance grain boundary conductivity. The process achieves simultaneous enhancement of both bulk and grain boundary conduction through a single-step procedure. Comparative analysis of sintering temperatures and ionic conductivities among NASICON solid electrolytes synthesized via different methods demonstrates flame-synthesized nanoparticles offer superior performance and reduced post-treatment costs, owing to their exceptional nano-scale sinterability and uniform elemental distribution.
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All authors Tianyi Wu, Yiyang Zhang, Zhu Fang, Shuting Lei, Xing Jin, Shuiqing Li

Materials Science

Porous-B$_{18}$: An Ideal Topological Semimetal with Symmetry-Enforced Orthogonal Nodal-Line and Nodal-Surface States

Xiao-jing Gao, Yanfeng Ge and Yan Gao

Topological semimetals (TSMs) featuring symmetry-protected band degeneracies have attracted considerable attention due to their exotic quantum properties and potential applications. While nodal line (NL) and nodal surface (NS) semimetals have been extensively studied, the realization of a material where both NL and NS coexist and are intertwined, particularly with an ideal electronic band structure, remains a significant challenge. Here, we predict via first-principles calculations and symmetry analysis a metastable boron allotrope, Porous-B$_{18}$ (space group $P6_3/m$, No.~176), as a pristine TSM hosting a NS and two straight NLs near the Fermi level. The structure, a honeycomb-like porous 3D framework, exhibits excellent dynamical, thermal (stable up to 1000~K), and mechanical stability. Its electronic band structure is remarkably clean: only the highest valence band (HVB) and the lowest conduction band (LCB) cross linearly within a large energy window of 1.84~eV, free from trivial-band interference. The nodal surface lies on the $k_z = \pm \pi$ planes, protected by combined time-reversal symmetry ($T$) and twofold screw-rotational symmetry ($S_{2z}$), yielding a full-plane Kramers-like degeneracy. The two nodal lines along $K$–$H$ and $K'$–$H'$ are protected by inversion and time-reversal symmetries, carry a quantized Berry phase of $\pm \pi$, and connect orthogonally to the nodal surface, forming an intertwined nodal network. Drumhead surface states on the $(1\bar{1}0)$ surface further confirm the nontrivial topology. Porous-B$_{18}$ thus provides an ideal platform for investigating the interplay between nodal-line and nodal-surface fermions and exploring novel quantum transport phenomena.
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Materials Science

Critical temperatures of two dimensional magnets beyond linear spin wave theory: application to CrI$_3$, MPS$_3$ (M=Ni, Mn, Fe) and CrSBr

Varun Rajeev Pavizhakumari and Thomas Olsen

Magnetic anisotropy is crucial for sustaining long range magnetic order in two-dimensional materials (2D) and must be taken into account by any approximate scheme for calculating critical temperatures. While 2D ferromagnets have received significant attention with regard to predicting Curie temperatures, the treatment of 2D anti-ferromagnetism has largely been restricted to classical approaches, which typically underestimate Néel temperatures. The concept of anti-ferromagnetism can be regarded as a special case of single-$Q$ magnetic order, and for such systems the critical temperature can be calculated from the magnon dispersion using either Holstein-Primakoff (HP) bosonization or Green's function-based Random Phase Approximation (RPA). Here, we study the effects of single-ion anisotropy in general single-$Q$ systems in both the HP and RPA methods. In the case of RPA, we generalize the approach to include the Callen Decoupling (CD) correction, which has previously been shown to yield good agreement with experimental Curie temperatures for 2D ferromagnets. We compare the calculated critical temperatures of CrI$_3$ (uniaxial ferromagnet), MPS$_3$ (M=Ni, Mn, Fe) (uniaxial anti-ferromagnets) and CrSBr (triaxial ferromagnet) monolayers with experimental values and find that the Green's function-based methods are much more reliable than HP and that the CD decoupling appears to be more accurate than RPA if the single-ion anisotropy is large.
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Materials Science

Identification of Empirical Constitutive Models for Age-Hardenable Aluminium Alloy and High-Chromium Martensitic Steel Using Symbolic Regression

Evgeniya Kabliman and Gabriel Kronberger

Process-structure-property relationships are fundamental in materials science and engineering and are key to the development of new and improved materials. Symbolic regression serves as a powerful tool for uncovering mathematical models that describe these relationships. It can automatically generate equations to predict material behaviour under specific manufacturing conditions and optimize performance characteristics such as strength and elasticity. The present work illustrates how symbolic regression can derive constitutive models that describe the behaviour of various metallic alloys during plastic deformation. Constitutive modelling is a mathematical framework for understanding the relationship between stress and strain in materials under different loading conditions. In this study, two materials (age-hardenable aluminium alloy and high-chromium martensitic steel) and two different testing methods (compression and tension) are considered to obtain the required stress-strain data. The results highlight the benefits of using symbolic regression while also discussing potential challenges.
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Materials Science

Revealing the Hidden Third Dimension of Point Defects in Two-Dimensional MXenes

Grace Guinan, Michelle A. Smeaton, Brian C. Wyatt et al. (+6 more)

Point defects govern many important functional properties of two-dimensional (2D) materials. However, resolving the three-dimensional (3D) arrangement of these defects in multi-layer 2D materials remains a fundamental challenge, hindering rational defect engineering. Here, we overcome this limitation using an artificial intelligence-guided electron microscopy workflow to map the 3D topology and clustering of atomic vacancies in Ti$_3$C$_2$T$_X$ MXene. Our approach reconstructs the 3D coordinates of vacancies across hundreds of thousands of lattice sites, generating robust statistical insight into their distribution that can be correlated with specific synthesis pathways. This large-scale data enables us to classify a hierarchy of defect structures–from isolated vacancies to nanopores–revealing their preferred formation and interaction mechanisms, as corroborated by molecular dynamics simulations. This work provides a generalizable framework for understanding and ultimately controlling point defects across large volumes, paving the way for the rational design of defect-engineered functional 2D materials.
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All authors Grace Guinan, Michelle A. Smeaton, Brian C. Wyatt, Steven Goldy, Hilary Egan, Andrew Glaws, Garritt J. Tucker, Babak Anasori, Steven R. Spurgeon

Materials Science

Machine-learning interatomic potential for AlN for epitaxial simulation

Nicholas Taormina, Emir Bilgili, Jason Gibson et al. (+3 more)

A machine learned interatomic potential for AlN was developed using the ultra-fast force field (UF3) methodology. A strong agreement with density functional theory calculations in predicting key structural and mechanical properties, including lattice constants, elastic constants, cohesive energy, and surface energies has been demonstrated. The potential was also shown to accurately reproduce the experimentally observed atomic core structure of edge dislocations. Most significantly, it reproduced the experimentally observed wurtzite crystal structure in the overlayer during homoepitaxial growth of AlN on wurtzite AlN, something that prior potentials failed to achieve. Additionally, the potential reproduced the experimentally observed layer-by-layer growth mode in the epilayer. The combination of accuracy, transferability, and computational speed afforded by the UF3 framework thus makes large-scale, atomistic simulations of epitaxial growth of AlN feasible.
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All authors Nicholas Taormina, Emir Bilgili, Jason Gibson, Richard Hennig, Simon Phillpot, Youping Chen