Materials Science
Beta-AlGaO/Ga2O3 Tri-Gate MOSHEMT with 70GHz fT and 55GHz fmax
Noor Jahan Nipu, Chinmoy Nath Saha and Uttam Singisetti
We report Beta-AlGaO/Ga2O3 tri-gate
heterostructure MOSHEMTs incorporating a thin 5 nm Al2O3 gate
oxide layer for improved gate control and reduced leakage. The devices were fabricated on AlGaO/GaO
heterostructures grown by ozone MBE on Fe-doped Ga2O3 (010) substrates. The tri-gate MOSHEMTs, with 1 micron-wide fins and Lg=155 nm, exhibit a peak current-gain cut-off frequency fT=70 GHz and a power-gain cut-off frequency fMAX=55 GHz.The fT.L product of 10.85 GHz-micron is the highest among reported Ga2O3 FETs to date. The devices show Vth =-0.5 V, an on/off ratio 10^6 I=80 mA/mm, a peak gm=60 mS/mm, and a low gate leakage current of 10^(-10) mA/mm at Vgs=0.5 V. Passivation with a 100 nm ALD Al2O3 layer effectively removes DC/RF dispersion and maintains stable operation under pulsed IV and repeated RF measurements. These results demonstrate the potential of tri-gate AlGaO/GaO MOSHEMTs for next-generation high-frequency and high-power applications.
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Materials Science
Machine Learning Guided Polymorph Selection in Molecular Beam Epitaxy of In2Se3
Ryan Trice, Mingyu Yu, Eric Welp et al. (+3 more)
Indium selenide (In2Se3), a layered chalcogenide with multiple polymorphs, is a promising material for optoelectronic and ferroelectric applications. However, achieving polymorph-pure thin films remains a major challenge due to the complex growth space. In this work,
Bayesian optimization (BO) is successfully leveraged to guide the molecular beam epitaxy growth of In2Se3 on Al2O3 substrates. By training a predictive Gaussian process regressor with sequential learning, we efficiently explored substrate temperature, indium flux, selenium flux, and cracker temperature, reducing experimental trials required for successful synthesis. A {\gamma}-In2Se3 film with 91% phase purity was achieved in fewer than 10 BO run samples. Attempts to isolate {\alpha}-In2Se3 were limited by amorphous film formation at low temperatures, indicating that single-step codeposition is unsuitable for crystalline {\alpha}-In2Se3 on Al2O3. Overall, this study validates BO as a powerful approach for phase-selective growth in complex material systems.
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All authors Ryan Trice, Mingyu Yu, Eric Welp, Morgan Applegate, Wesley Reinhart, Stephanie Law
Materials Science
Magnetism and 3D Electron Diffraction Solution of Hydrated Rubidium-Ruthenium Oxide Rb$_2$Ru$_2$O$_7$.H$_2$O
Krystof Chrappova, Jeremiah P. Tidey, Christopher Bell et al. (+1 more)
The
crystal structure of Rb$_2$Ru$_2$O$_7$.H$_2$O was determined by three-dimensional electron diffraction from the individual crystallites of a solid-state powder product. Rb$_2$Ru$_2$O$_7$.H$_2$O crystallizes in space group C2/c ($a=7.841(3)$ Å, $b=12.500(3)$ Å, $c=8.392(2)$ Å, $\beta=93.57(4)^\circ$, Z=4). The structure contains infinite chains that run normal to the (101) plane and consist of alternating RuO$_6$ octahedra and square-pyramidal RuO$_5$ units connected via shared O-O edges.
Magnetic properties were measured on the bulk powder, showing a diamagnetic baseline from 300 to 60 K with a small Curie tail below 55 K. The
magnetic moment, calculated from the 1.8 K isotherm, saturates at $M=4.4\times10^{-3}\,\mu_\mathrm{B}\,\mathrm{Ru}^{-1}$, much less than would be expected for $S=1$ ruthenium. Bond-valence-sum analysis indicates high-valent Ru, and the near-diamagnetic response is consistent with the edge-sharing Ru-Ru motif, where weak direct Ru-Ru overlap yields a local singlet.
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All authors Krystof Chrappova, Jeremiah P. Tidey, Christopher Bell, Simon R. Hall
Materials Science
Disentangling the Discrepancy Between Theoretical and Experimental Curie Temperatures in Ferroelectric PbTiO$_3$
Denan Li, Christian S. Ahart and Shi Liu
Accurately predicting the Curie temperature ($T_c$) of ferroelectrics from first principles remains a major challenge, as theoretical estimates often fall significantly below experimental values. In this work, we investigate the origin of these discrepancies in the prototypical ferroelectric PbTiO$_3$ by performing extensive constant-pressure ab initio molecular dynamics (AIMD) simulations and benchmarking them against classical molecular dynamics (MD) using machine learning force fields (MLFFs) derived from first-principles data. Our results show that the underestimation of $T_c$ primarily stems from the limitations of the exchange-correlation functional, rather than inaccuracies in the MLFF fitting. We uncover a critical interplay between finite-size effects and the range of interatomic interactions: although short-range MLFFs appear to yield better agreement with experimental $T_c$, this improvement results from a fortuitous cancellation of errors. Incorporating explicit long-range interactions improves accuracy for larger supercells but ultimately leads to lower predicted $T_c$ values. These findings highlight that accurate finite-temperature predictions require not only high-quality training data and sufficiently large simulation
cells, but also the explicit treatment of long-range interactions and improved exchange-correlation functionals.
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Materials Science
Robust phonon engineering and symmetry-selective lattice dynamics in CrSBr$_{1-x}$Cl$_{x}$
Satyam Sahu, Arsalan Hashemi, Mahdi Ghorbani-Asl et al. (+9 more)
Atomic substitution provides a controlled route to engineer
lattice dynamics in low-
symmetry two-dimensional materials. Here, by combining polarization-resolved Raman spectroscopy and first-principles calculations, we investigate the
evolution of
phonon characteristics in CrSBr$_{1-x}$Cl$_{x}$ ($0 \leq x \leq \sim 0.5$) upon partial substitution of Br with Cl atoms. Progressive Cl substitution of Br induces systematic shifts of parent CrSBr out-of-plane $A_\textrm{g}$
phonon modes and activates additional Raman features. These features persist across different polarization configurations and excitation energies, reflecting substitution-induced
symmetry lowering and local
lattice perturbations. Explicit supercell
phonon calculations combined with Raman $\Gamma$-density-of-states simulations identify these features as
symmetry-lowered descendants of parent modes arising from
alloy disorder. Complementary strain-dependent calculations reveal that anisotropic
lattice compression plays a key role in renormalizing Cr-S dominated
phonons. Under near-resonant excitation, stimulated Raman scattering-like amplification remains observable with increasing Cl content, highlighting the resilience of anisotropic electron-
phonon coupling in this system.
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All authors Satyam Sahu, Arsalan Hashemi, Mahdi Ghorbani-Asl, János Koltai, Jan Maňák, Bing Wu, Aljoscha Söll, Zdeněk Sofer, Mikko Karttunen, Arkady V. Krasheninnikov, Matěj Velický, Otakar Frank
Materials Science
Photoelectron Spectroscopy Study of U-Te Thin Films: A Unified Perspective of Hybridization Effects across Compositions
E. A. Tereshina-Chitrova, S. G. Alex, O. Koloskova et al. (+6 more)
Uranium tellurides span
magnetic and superconducting ground states, yet systematic electronic-structure information across the U-Te series remains scarce. In this study, we perform photoemission measurements on freshly prepared UxTey thin films covering the range of bulk stoichiometries under ultra-high
vacuum (10^-9 Pa), enabling clean surfaces and compositions matching bulk phases, including the celebrated UTe2. X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS) reveal consistent
evolution of the U 4f and Te 3d core levels and valence states across the series, in good agreement with the limited bulk data. Supported by uniform ab initio calculations for all U-Te compounds, we identify systematic trends in U-Te hybridization and charge-transfer effects across the series. These results establish thin-film photoemission as a reliable route for mapping electronic-structure trends in tellurides of heavy elements with diverse electronic ground states.
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All authors E. A. Tereshina-Chitrova, S. G. Alex, O. Koloskova, L. Havela, L. Horak, O. Romanyuk, F. Huber, T. Gouder, M. Divis
Materials Science · Cross-listed from cond-mat.supr-con
Spin-density-wave transition in monolayer-trilayer La3Ni2O7 single crystals
Mingxin Zhang, Jie Dou, Di Peng et al. (+17 more)
The recent discovery of high-temperature superconductivity in pressurized Ruddlesden-Popper nickelates stimulated intense research into their correlated electron physics. Establishing the diversity of ground states across different Ruddlesden-Popper phases is crucial for elucidating the superconducting mechanisms in these nickelates. Motivated by the recent report of superconductivity in hybrid 1212-type La5Ni3O11, we synthesized and investigated the long-range-ordered hybrid 1313-type La3Ni2O7. In contrast to its
bilayer counterpart, the 1313-type La3Ni2O7 exhibits characteristic semiconducting behavior at ambient pressure, displaying a distinct anomaly at 170 K. This behavior is consistently evidenced by measurements of both
magnetic susceptibility and specific heat.
Nuclear magnetic resonance spectroscopy unambiguously indicates a
spin-density-wave transition occurring at 170 K. High-pressure electrical transport measurements demonstrate the induction of metallization under pressure, yet reveal no discernible traces of superconductivity up to 65 GPa. Our findings establish hybrid 1313-type La3Ni2O7 as a new member of the Ruddlesden-Popper nickelate family exhibiting a distinct
spin-density-wave transition, and offers a new platform for investigating the interplay among
crystal structure, electronic orders, and superconductivity in hybrid nickelates.
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All authors Mingxin Zhang, Jie Dou, Di Peng, Cuiying Pei, Qi Wang, Yi Zhao, Chao Xiong, Shuo Li, Jun Luo, Juefei Wu, Lingxiao Zhao, Qing Zhang, Jie Yang, Yulin Chen, Jinkui Zhao, Wenge Yang, Hanjie Guo, Qiaoshi Zeng, Rui Zhou, Yanpeng Qi
Materials Science · Cross-listed from cond-mat.supr-con
Weakly anisotropic superconductivity of Pr4Ni3O10 single crystals
Cuiying Pei, Yang Shen, Di Peng et al. (+17 more)
Since the discovery of high-temperature superconductivity, studying the upper critical field and its anisotropy has been crucial for understanding superconducting mechanism and guiding applications. Here we perform in situ high-pressure angular-dependent electrical transport measurements on Pr4Ni3O10 single
crystals using a custom diamond anvil
cell (DAC) rotator and confirming its anisotropic superconductivity. The anisotropy parameter is approximately 1.6, decreasing with increasing temperature and approaches 1 near Tc. Comparing effective mass anisotropy and inter-block distance in cuprates and iron-based
superconductors (FeSCs) reveals that Pr4Ni3O10 single
crystals superconductors are consistent with a two-band model, where intralayer
quantum confinement within the unit
cell induces interlayer coherence, thereby leading to three-dimensional (3D) superconductivity. This study not only establishes the existence of anisotropic superconductivity in bulk Ruddlesden-Popper nickelates, but also provide critical insight into the role of dimensionality in high-temperature superconductivity.
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All authors Cuiying Pei, Yang Shen, Di Peng, Mingxin Zhang, Yi Zhao, Xiangzhuo Xing, Qi Wang, Juefei Wu, Junjie Wang, Lingxiao Zhao, Zhenfang Xing, Yulin Chen, Jinkui Zhao, Wenge Yang, Xiaobing Liu, Zhixiang Shi, Hanjie Guo, Qiaoshi Zeng, Guang-Ming Zhang, Yanpeng Qi
Materials Science
Phase Transitions in Low-Dimensional Layered Double Perovskites: The Role of the Organic Moieties
Beatriz Martín-García, Davide Spirito, Giulia Biffi et al. (+3 more)
Halide double perovskites are an interesting alternative to Pb-containing counterparts as active materials in optoelectronic devices. Low-dimensional double perovskites are fabricated by introducing large organic cations, resulting in organic/inorganic architectures with one or more inorganic octahedral layers separated by organic cations. Here, we synthesize layered double perovskites based on 3D Cs2AgBiBr6 that consist of double (2L) or single (1L) inorganic octahedral layers, using ammonium cations of different size and chemical structure. Temperature-dependent Raman spectroscopy reveals phase transition signatures in both inorganic
lattice and organic moieties by detecting variations in their vibrational modes. Changes in the conformational arrangement of the organic cations to an ordered state coincide with a phase transition in the 1L systems with the shortest ammonium moieties. Significant changes of photoluminescence intensity observed around the transition temperature suggest that optical properties may be deeply affected by the octahedral tilts emerging at the phase transition.
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All authors Beatriz Martín-García, Davide Spirito, Giulia Biffi, Sergey Artyukhin, Francesco Bonaccorso, Roman Krahne
Materials Science · Cross-listed from cond-mat.mes-hall
Topological Charges, Fermi Arcs, and Surface States of $K_4$ Crystal
Shoya Yoshida, Katsuhiro Takahashi and Katsunori Wakabayashi
We investigate the topological electronic properties of the $K_4$
crystal by constructing a tight-binding model. The bulk band structure hosts Weyl nodes with higher and conventional chiralities ($\chi = \pm 2$ and $\chi = \pm 1$) located at high-
symmetry points in the Brillouin zone. Through analytical evaluation of the Berry
curvature, we identify the positions and chiralities of these Weyl nodes. Furthermore, slab calculations for the (001) surface reveal
Fermi arcs that connect Weyl nodes of opposite chirality, including those linking $\chi = \pm 2$ nodes with pairs of $\chi = \mp 1$ nodes. These results demonstrate that the $K_4$
crystal is a spinless Weyl semimetal featuring topologically protected surface states originating from multiple types of Weyl nodes.
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Materials Science
Visual Luminescence Thermometry Enabled by Phase-Transition-Activated Cross Relaxation of Tb3+ Ions
L. Marciniak and M. Szymczak
The development of visual luminescent thermometers capable of exhibiting pronounced color changes in response to temperature variations requires the rational design of phosphors with high spectrally selective thermal sensitivity. In this work, we present a strategy based on phase-transition-induced activation of cross-relaxation processes in LiYO2:Tb3+. The monoclinic-to-tetragonal structural phase transition modifies the point
symmetry of Tb3+ ions in the host
lattice, enhances the Stark effect, and enables energetic resonance required for efficient cross relaxation. Consequently, emission originating from the 5D3 excited state is rapidly quenched relative to that from the 5D4 level above approximately 300 K, resulting in a distinct temperature-dependent color change of the emitted light from blue to green. This mechanism yields exceptionally high chromaticity-coordinate-based sensitivities, reaching SRx,max = 0.40% K-1 and SRy,max=0.72% K-1 at 410 K. Furthermore, phase-transition-driven modifications of the Tb3+ emission spectral profile enable the realization of a multimode luminescent thermometer with a maximum relative sensitivity of SRmax=13% K-1. The practical applicability of this system is demonstrated through an ON-OFF luminescent thermal switch and fully filter-free, dynamic two-dimensional thermal imaging using the blue and green channels of a standard digital camera, enabling intuitive visualization, remote readout, and temperature mapping under dynamic conditions.
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Materials Science
Machine learning interatomic potentials for solid-state precipitation
Lorenzo Piersante and Anirudh Raju Natarajan
Machine learning interatomic potentials (MLIPs) are routinely used to model diverse atomistic phenomena, yet parameterizing them to accurately capture solid-state phase transformations remains difficult. We present error metrics and data-generation schemes designed to streamline the parameterization of MLIPs for modeling precipitation in multi-component
alloys. We developed an
algorithm that enumerates symmetrically distinct transformation pathways connecting chemical decorations on different parent
crystal structures. Additionally, we introduce the weighted Kendall-$\tau$ coefficient and its semi-grand canonical generalization as metrics for quantifying MLIP accuracy in predicting low-temperature thermodynamics. We apply these approaches to parameterize an MLIP for a dilute Mg-Nd
alloy. The resulting potential reproduces the complex early-stage precipitation behavior observed in experiment. Large-scale atomistic simulations reveal competition between order-disorder and structural transformations. Furthermore, these results suggest a continuous transition between high-
symmetry hcp and bcc
crystal structures during aging heat treatments.
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Materials Science · Cross-listed from physics.optics
Dislocation Entropy: Temperature and Density Dependence
A. G. Sukharev
Laser hardening of metals occurs under the influence of a shock wave, which changes the distribution and density of one-dimensional defects - dislocations. There is a relationship between the density of dislocations, the grain size and the resistance of a single
crystal to shear loading. The mechanism of hardening processes continues to be intensively studied, and the dynamics of defects plays a central role here. In this paper, the dislocation
entropy is analyzed from a combinatorial point of view and from the point of view of a physical oscillator with a given energy reserve. Both contributions play an important role in describing the free energy of a one-dimensional ensemble of dislocations, and are necessary to take into account the dynamic processes inside the grain of a polycrystalline structure. Keywords:
Laser Shock Peening, statistical mechanics
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Materials Science
Water Phase Diagram from a General-Purpose Atomic Cluster Expansion Potential
Eslam Ibrahim, Yury Lysogorskiy, Ralf Drautz et al. (+1 more)
Water's phase diagram remains one of the most intricate and challenging
benchmarks in molecular modeling. In this study, we compute the phase diagram of water using an Atomic Cluster Expansion (ACE) potential trained on density-functional theory (DFT) calculations based on the revPBE-D3 exchange and correlation functional. We compute solid-
liquid chemical potential differences and melting points using biased coexistence simulations with the On-the-Fly Probability Enhanced Sampling (OPES) method. Starting from these points, we trace coexistence lines using Gibbs-Duhem integration. This combination of methods allows us to consistently map pressure-temperature phase boundaries and reconstruct the full phase diagram between approximately 100-500 K and 0-4 GPa. The stability regions of the main ice polymorphs (Ih, II, V, VI, and VII) are reproduced in close agreement with experiments. As in earlier studies based on DFT, ice III is metastable and there are systematic shifts of coexistence lines with respect to experimental results. Our results demonstrate the capability of our general-purpose ACE potential to capture the complex phase behavior of water across wide thermodynamic conditions.
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All authors Eslam Ibrahim, Yury Lysogorskiy, Ralf Drautz, Pablo Piaggi
Materials Science · Cross-listed from cond-mat.soft
Multiscale Prediction of Polymer Relaxation Dynamics via Computational and Data-Driven Methods
Nguyen T. T. Duyen, Ngo T. Que and Anh D. Phan
We present a multiscale modeling approach that integrates molecular dynamics simulations, machine learning, and the Elastically Collective Nonlinear Langevin Equation (ECNLE) theory to investigate the glass transition dynamics of
polymer systems. The glass transition temperatures (Tg) of four representative
polymers are estimated using simulations and machine learning model trained on experimental
datasets. These predicted Tg values are used as inputs to the ECNLE theory to compute the temperature dependence of structural relaxation times and
diffusion coefficients, and the dynamic fragility. The Tg values predicted from simulations show good quantitative agreement with experimental data. While machine learning tends to slightly overestimate Tg, the resulting dynamic fragility values remain close to experimental fragilities. Overall, ECNLE calculations using these inputs agree well with broadband dielectric spectroscopy results. Our integrated approach provides a practical and scalable tool for predicting the dynamic behavior of
polymers, particularly in systems where experimental data are limited.
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Materials Science · Cross-listed from eess.IV
PYVALE: A Fast, Scalable, Open-Source 2D Digital Image Correlation (DIC) Engine Capable of Handling Gigapixel Images
Joel Hirst, Lorna Sibson, Adel Tayeb et al. (+10 more)
Background: Digital Image Correlation (DIC) is a widely used full-field measurement technique, but both open-source and commercial packages often have limitations such as operating-system restrictions, lack of support for deployment on computing clusters, and poor scalability to gigapixel-scale images common in Scanning Electron Microscopy DIC (SEM-DIC). Objective: Pyvale is an open-source software package designed for sensor simulation, uncertainty quantification, placement optimization, and calibration/validation. A key component of this is the development of a dedicated 2D DIC module intended for standalone use and integration within broader workflows. Methods: Pyvale provides a user-friendly Python interface with performant compiled routines underneath. At its core is a multithreaded, reliability-guided DIC
algorithm. Its open-source MIT license enables wide deployment, including on computing clusters and in automated pipelines. Results: Benchmarking with the publicly available 2D DIC challenge 2.0
dataset shows that Pyvale achieves metrological performance comparable to existing commercial and open-source DIC codes. It can correlate gigapixel-scale image pairs in under 5 minutes on high-specification desktop workstations, with
memory peaking at approximately 50 GB. Conclusions: Pyvale's strong metrological foundation, coupled with its scalability for SEM-DIC, positions it as a platform for sustained, community-driven development. Its design and licensing provide a foundation for future improvements in open-source DIC and integration into experimental design and validation workflows.
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All authors Joel Hirst, Lorna Sibson, Adel Tayeb, Ben Poole, Megan Sampson, Wiera Bielajewa, Michael Atkinson, Alex Marsh, Rory Spencer, Rob Hamill, Cory Hamelin, Allan Harte, Lloyd Fletcher
Materials Science
Effect of uniaxial compressive stress on polarization switching and domain wall formation in tetragonal phase BaTiO3 via machine learning potential
Po-Yen Chen and Teruyasu Mizoguchi
Ferroelectric materials such as BaTiO3 exhibit spontaneous polarization that can be reoriented by an external electric field, forming the basis of various
memory, actuator, and sensor applications. The polarization switching behavior, however, is strongly influenced by mechanical boundary conditions due to the intrinsic electromechanical coupling in ferroelectrics. In this study, we employ a machine learning interatomic potential to investigate the effect of uniaxial compressive stress on polarization switching and domain wall
evolution in the tetragonal phase of BaTiO3. This study revealed a critical stress about 120 MPa which 90 degree polarization switching occurs. Beyond the critical stress, larger supercells exhibit lower activation energies for polarization switching with 180-degree domain wall formation and weaker constraints from periodic boundary conditions, thereby facilitating domain-wall formation. Besides, Increasing compressive stress reduces both the remnant polarization and the coercive field, while a double hysteresis loop emerges at a stress level of 80 MPa. These findings provide atomistic insights into stress-controlled ferroelectric switching and highlight the crucial role of mechanical loading in designing reliable ferroelectric devices.
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Materials Science · Cross-listed from cond-mat.str-el
Emergent Gauge Flux and Spin Ordering in Magnetized Triangular Spin Liquids: Applications to Hofstadter-Hubbard Model
Jiahao Yang, Hao Tian, Si-Yu Pan et al. (+1 more)
Motivated by recent progress in moiré superlattices and
spin-1/2 triangular-
lattice antiferromagnets, we study how orbital
magnetic flux and Zeeman coupling compete or cooperate in generating internal U(1) gauge flux in a triangular
spin liquid. We show that orbital flux favors a
chiral spin liquid with staggered internal flux, whereas Zeeman coupling destabilizes the spinon
Fermi-pocket state toward a Landau-level state with spontaneous uniform internal flux and conical
spin order. We demonstrate this mechanism in a
spin-$1/2$ $J_1$-$J_2$-$J_{\chi}$ model, and further identify thermal
Hall and
magnetic signatures that distinguish these regimes, with potential applications to moiré Hofstadter-Hubbard systems and triangular-
lattice antiferromagnets.
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All authors Jiahao Yang, Hao Tian, Si-Yu Pan, Gang v. Chen
Materials Science
Discovery of Ferroelectric Twin Boundaries in a Photoactive Halide Perovskite
Weilun Li, Qimu Yuan, Michael B. Johnston et al. (+1 more)
Halide perovskites have emerged as promising materials for next-generation photovoltaics,
laser sources and X-ray detectors. There is intense debate as to whether some photoactive halide perovskites exhibit ferroelectric behaviour and whether it might be possible to utilise the bulk photovoltaic effect to enhance the performance of halide perovskite
solar cells. Here, using low-dose scanning transmission electron microscopy, we discover the existence of ferroelastic twin boundaries in vapor-deposited CsPbI3 thin films, parallel to {110} and {112}. Remarkably, despite photoactive CsPbI3 being centrosymmetric and non-polar, we observe directly that Pb atoms shift at {110} twin boundaries driving a local ferroelectric-like polarisation. These polar twin walls form an intrinsic array of nanoscale functional interfaces, spaced ~30-50 nm apart, embedded within the non-polar perovskite
lattice. In contrast, {112} twin boundaries remain non-polar but strongly suppress octahedral tilt and off-centre Cs atom displacements, revealing a different untapped ferroic degree of freedom. These discoveries together uncover previously hidden ferroic functionality in halide perovskite
semiconductors, opening opportunities for enhanced conductivity and photovoltaic behaviour through domain wall engineering.
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All authors Weilun Li, Qimu Yuan, Michael B. Johnston, Joanne Etheridge
Materials Science
Engineering of Orbital Hybridization: An Exotic Strategy to Manipulate Orbital Current
Kun Zheng, Haonan Wang, Ju Chen et al. (+17 more)
Current-induced
spin-orbit torque (SOT) plays a crucial role in the next-generation
spin-orbitronics. Enhancing its efficiency is both fundamentally and practically interesting and remains a challenge to date. Recently, orbital counterparts of
spin effects that do not rely on the
spin-orbit coupling (SOC) have been found as an alternative mechanism to realize it. This work highlights the engineering of copper oxidation states for manipulating the orbital current and its torque in the CuO$_x$-based
heterostructures. The orbital hybridization and thus the orbital-Rashba-Edelstein effect at the CuO$_x$/Cu interfaces are significantly enhanced by increasing the copper oxidation state, yielding a torque efficiency that is almost ten times larger than the conventional heavy metals. The Cu$_4$O$_3$/Cu interface, rather than the widely accepted CuO/Cu interface, is revealed to account for the enhanced SOT performance in the CuO$_x$-based
heterostructures. In addition, the torque efficiency can be alternatively switched between high and low thresholds through the redox reaction. The current results establish an exotic and robust strategy for engineering the orbital current and SOT for
spin-orbitronics, which applies to other weak-SOC materials.
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All authors Kun Zheng, Haonan Wang, Ju Chen, Hongxin Cui, Jing Meng, Zheng Li, Cuimei Cao, Haoyu Lin, Yuhao Wang, Keqi Xia, Jiahao Liu, Xiaoyu Feng, Hui Zhang, Bocheng Yu, Jiyuan Li, Yang Xu, Zhengzhong Yang, Shijing Gong, Qingfeng Zhan, Tian Shang
Materials Science · Cross-listed from physics.acc-ph
Development of next-generation light-weight ternary Mg–Al–Li alloys for beampipe applications in particle accelerators
Kamaljeet Singh, Kangkan Goswami, Raghunath Sahoo et al. (+1 more)
The current study reports the design of advanced light-weight materials for high-energy accelerator beampipe applications. The objective is to optimize the combined requirements of high radiation length and stiffness properties of the designed materials. The present study targets conventional beampipe materials such as aluminum, titanium, and stainless steel as primary performance
benchmarks. These conventional beampipes are used at synchrotron radiation sources, such as Indus-1 and Indus-2 in India, the Nuclotron-based Ion
Collider Facility in Russia, and the ring synchrotron facility SIS 100/300 at the Facility for Antiproton and Ion Research in Germany. In this context, a series of ternary Mg–Al–Li
alloys is systematically investigated to enhance the figure of merit. Two aluminum–rich
alloys, A1 ($\mathrm{Al_{61.5}Li_{10.8}Mg_{27.7}}$) and A2 ($\mathrm{Al_{66}Li_{19.4}Mg_{14.6}}$), along with three magnesium-rich
alloys, M1 ($\mathrm{Al_{23.9}Li_{29.3}Mg_{46.8}}$), M2 ($\mathrm{Al_{19}Li_{20.6}Mg_{60.4}}$), and M3 ($\mathrm{Al_{39.8}Li_{20.1}Mg_{40.1}}$) are explored. Thermodynamic stability, density, liquidus temperature, and phases are evaluated using Latin hypercube sampling within the Thermo-Calc TC-Python framework. Elastic properties are obtained from density functional theory calculations performed using the Vienna Ab Initio Simulation Package. Our results show that, although the elastic
moduli ($E$) of the investigated Mg-Al-Li
alloys are comparable to those of conventional beampipe materials, their significantly higher radiation lengths ($X_0$) lead to an overall improvement in the figure of merit $X_0 E^{1/3}$.
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All authors Kamaljeet Singh, Kangkan Goswami, Raghunath Sahoo, Sumanta Samal
Materials Science
Inverse Chiral Phonon Zeeman Effect in Noncentrosymmetric Crystals
Jun-ichiro Kishine, A. S. Ovchinnikov, Masahiro Sato et al. (+2 more)
We present a microscopic theory of the inverse
chiral phonon Zeeman effect in noncentrosymmetric
crystals. Within micropolar elasticity, coupled translational displacements and microrotations give rise to intrinsically
chiral phonons, which generate an elliptically polarized internal
magnetic field through dynamical piezoelectricity. In the high-frequency Floquet regime and under incomplete electronic screening, this field acts as an effective longitudinal Zeeman field on electronic
spins, leading to
spin polarization and band splitting. The results establish a purely
lattice-driven mechanism for the inverse
chiral phonon Zeeman effect in noncentrosymmetric
crystals.
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All authors Jun-ichiro Kishine, A. S. Ovchinnikov, Masahiro Sato, G. N. Makarov, A. D. Lyakhov
Materials Science
Room temperature intrinsic anomalous Hall effect in disordered half-metallic ferromagnetic quaternary Heusler alloy CoRuFeSi
Manikantha Panda, Sonali S. Pradhan, Prabuddha Kant Mishra et al. (+6 more)
Quaternary Heusler
alloys offer a versatile platform for engineering
magnetic and topological transport phenomena through chemical flexibility and tunable disorder. Here, we report a comprehensive experimental and theoretical investigation of the
magnetic, magnetotransport, and anomalous
Hall properties of the quaternary Heusler
alloy CoRuFeSi. The compound crystallizes in the LiMgPdSn-type structure with significant Co–Ru antisite disorder and exhibits soft ferromagnetism with a saturation magnetization of $4.21~\mu_{\mathrm{B}}/\mathrm{f.u.}$ at low temperature and a Curie temperature well above room temperature.
Hall measurements reveal a robust anomalous
Hall effect persisting up to 300~K, with an anomalous
Hall conductivity of $\sim 74$~S/cm that is nearly temperature independent. Scaling analysis demonstrates that the anomalous
Hall response is dominated by the intrinsic Berry-
curvature mechanism. First-principles calculations identify CoRuFeSi as a topologically nontrivial nodal-line semimetal in its ordered phase. Incorporation of experimentally relevant Co–Ru antisite disorder redistributes the Berry
curvature and quantitatively reproduces the experimentally observed anomalous
Hall conductivity, while preserving half-
metallicity. These results establish CoRuFeSi as a disorder-tolerant half-metallic ferromagnet with a sizable intrinsic anomalous
Hall effect at room temperature, highlighting its potential for spintronic and
Hall-based device applications.
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All authors Manikantha Panda, Sonali S. Pradhan, Prabuddha Kant Mishra, Alapan Bera, Rosni Roy, Rajib Mondal, Soumik Mukhopadhyay, V. Kanchana, Tapas Paramanik
Materials Science
Lithium and sodium decorated PHE-graphene for high capacity hydrogen storage: A DFT and GCMC study
Hongyan Ma, Qing Wang, Huilin Sun et al. (+5 more)
Porous nanocarbon materials are seen as potential excellent materials for hydrogen storage due to their high surface area, excellent cycling stability and favorable kinetics. This study employs Density Functional Theory (DFT) simulations to investigate key property of Li$^-$ and Na$^-$ modified PHE-
graphene, including structural stability, electronic properties, and hydrogen storage capabilities. The results show that when each Li atom adsorbs six hydrogen molecules, the material reaches the maximum hydrogen adsorption gravimetric density of 15.20 wt%. Additionally, through Grand Canonical Monte Carlo (GCMC) simulations, we obtained the hydrogen weight ratios and adsorption enthalpy curves for Li- and Na-modified PHE under varying temperature and pressure conditions. These findings indicate that both Li- and Na-modified PHE-
graphene are exceptional candidates for hydrogen storage materials, particularly in mobile applications.
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All authors Hongyan Ma, Qing Wang, Huilin Sun, Qingyu Li, Yunhui Wang, Zhihong Yang, Huaihong Zhao, Huazhong Shu
Materials Science
Quantum theory of elastic strings and the thermal conductivity of glasses
Fernando Lund and Bruno Scheihing-Hitschfeld
We study the thermal conductivity of amorphous solids by constructing a continuum model whose degrees of freedom are propagating vibrational modes (
phonons) and extended Volterra dislocation line defects with their own vibrational degrees of freedom which do not propagate in space. Our working assumption is that these additional degrees of freedom account for the "
boson peak" that is observed in glassy materials. This identification allows us to obtain the length distribution of dislocations from experimental data of the
boson peak for each material, which we use as input to calculate the
phonon self-energy in a
quantum field theory framework using that the
phonon-dislocation interaction is given by the Peach-Koehler force. The tail of the distribution for long dislocations is consistent with an $L^{-5}$ power law. Our results show that this power law yields a linear rise in the thermal conductivity, as observed in glasses at low temperatures. We then consider two approaches to describe thermal conductivity data quantitatively. In the simplest approach we only keep the low-frequency behavior of the
phonon self-energy with one free parameter, plus an adjustable UV cutoff. In the more realistic approach we keep the full frequency dependence of the
phonon self-energy as dictated by the
phonon-dislocation interaction plus an additional contribution due to scattering with point defects, with a cutoff set by the typical interatomic spacing of the material. We obtain a satisfactory description of thermal conductivity data with both approaches. We conclude by discussing prospects to test the predictive power of this model.
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Materials Science · Cross-listed from physics.optics
Purely equatorial lasing in spherical liquid crystal polymer microlasers with bipolar refractive index profile
David Ripp, Nachiket Pathak, Vera M. Titze et al. (+3 more)
Liquid crystal whispering gallery mode (WGM) microlasers show high sensitivity to external stimuli and distinct spectral features, rendering them ideally suited for various sensing applications. They also offer intrinsic anisotropic optical properties, which can be used to shape and manipulate light even inside spatially highly symmetric structures. Here, we report the fabrication of a spherical bipolar
liquid crystal polymer microlaser that tightly confines the optical path of WGMs to the equatorial plane. By controlled anchoring of the
liquid crystal mesogens followed by polymerization, a fixed refractive index profile is formed within the spherical microcavity. Consequently, only transverse electric (TE) modes oscillating in the equatorial plane experience the high extraordinary refractive index, allowing to confine lasing into a single plane. Furthermore, we observe a characteristic splitting into sub-modes. By combining hyperspectral imaging, optical modeling, and theoretical calculations, we show that the observed sub-modes originate from the lifting of the energy degeneracy of azimuthal WGMs. The unique ability to confine lasing into a single plane makes these spherical microlasers independent of the exact position of the pump beam, which allows consistent localized sensing especially in combination with fast point scanning microscopes or inside highly dynamic biological environments.
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All authors David Ripp, Nachiket Pathak, Vera M. Titze, Catriona A. Thomson, Andreas Mischok, Marcel Schubert
Materials Science
3D atomistic imaging of polymer nanocomposites with Atom Probe Tomography: experimental methodology, preliminary results and future outlook
James O. Douglas, Reza Salehiyan, Aparna Saksena et al. (+5 more)
The use of
polymer nanocomposites as gas barrier materials has seen increasing interest, including applications involving hydrogen transport and storage. Better understanding of gas transport through those polymeric systems requires 3D nanoscale detection of distributions and the possible trapping of gas molecules within nanoparticles and
polymer/nanoparticle interfaces While atom probe
tomography (APT) offers promising means for such nanoscale characterisation, its use for
polymers has been mainly limited to thin organic layers deposited onto substrates or pre-fabricated metal needle shaped specimens. This work provides the very first application of APT to bulk
polymer nanocomposites. Particularly, site specific atom probe sample preparation by Focused Ion Beam (FIB) liftout has been shown for the first time in a model system of hexagonal boron nanoparticles within a PVDF
polymer matrix, using a variety of FIB workflows including Xe FIB, Ga FIB, cryogenic Ga FIB and deuterium charging. Mass spectra from the bulk
polymer and the nanoparticle were collected using pulsed
laser atom probe using standard conditions and compared. Several challenges encountered during this research including damage of the polymeric
matrix during sample preparation were extensively discussed in this paper. Once those challenges have been resolved (e.g. by developing site specific sample preparation protocols), the application of APT to
polymer nanocomposites can open new options for nanoscale characterisation of those systems.
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All authors James O. Douglas, Reza Salehiyan, Aparna Saksena, Tim M. Schwarz, Baptiste Gault, Stella Pedrazzini, Emilio Martinez-Paneda, Łukasz Figiel
Materials Science · Cross-listed from physics.chem-ph
Enhanced Climbing Image Nudged Elastic Band method with Hessian Eigenmode Alignment
Rohit Goswami, Miha Gunde and Hannes Jónsson
Accurate determination of transition states is central to an understanding of reaction kinetics. Double-endpoint methods where both initial and final states are specified, such as the climbing image nudged elastic band (CI-NEB), identify the minimum energy path between the two and thereby the saddle point on the energy surface that is relevant for the given transition, thus providing an estimate of the transition state within the harmonic approximation of transition state theory. Such calculations can, however, incur high computational costs and may suffer stagnation on exceptionally flat or rough energy surfaces. Conversely, methods that only require specification of an initial set of atomic coordinates, such as the minimum mode following (MMF) method, offer efficiency but can converge on saddle points that are not relevant for transition of interest. Here, we present an adaptive hybrid
algorithm that integrates the CI-NEB with the MMF method so as to get faster convergence to the relevant saddle point. The method is benchmarked for the Baker-Chan (BC) saddle point test set using the PET-MAD machine-learned potential as well as 59 transitions of a heptamer island on Pt(111) from the OptBench
benchmark set. A
Bayesian analysis of the performance shows a reduction in energy and force calculations of 57% [95% CrI: -64%, -50%] relative to CI-NEB for the BC set, while a 31% mean reduction is found for the transitions of the heptamer island. These results establish this hybrid method as a highly effective tool for high-throughput automated chemical discovery of atomic rearrangements.
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