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Hydrogen and deuterium tunneling in niobium

Physical Review B 2025年第2期111卷 L020103-L020103页

作者： Abdulaziz Abogoda W. A. Shelton I. Vekhter J. A. Sauls Hearne Institute for Theoretical Physics Louisiana State University Baton Rouge Louisiana 70803 USA Applied Physics Graduate Program Northwestern University Evanston Illinois 60208 USA Department of Physics and Astronomy Louisiana State University Baton Rouge Louisiana 70803 USA

We use density functional methods to identify the atomic configurations of H and D atoms trapped by O impurities embedded in bulk Nb. The O atoms are located at the octahedral position in the Nb body-centered cubic (BCC) lattice, and H (D) atoms tunnel between two degenerate tetrahedral sites separated by a mirror plane. Using nudged elastic band (NEB) methods, we calculate the double-well potential for O-H and O-D impurities and the wave functions and tunnel splittings for H and D atoms. Our results agree with those obtained from analysis of heat capacity and neutron scattering measurements on Nb with low concentrations of O-H and O-D.

关键词： Atoms

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Real-space screening of quantum spin-Hall insulators

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Physical Review Materials 2024年第12期8卷 124203-124203页

作者： Alexander C. Tyner Pallab Goswami Graduate Program in Applied Physics Northwestern University Evanston Illinois 60208 USA Department of Physics and Astronomy Northwestern University Evanston Illinois 60208 USA

It was shown by Prodan in 2009 that both magnetic and nonmagnetic two-dimensional insulators can support quantized spin-Chern number in the absence of spin-rotation symmetry as a bulk topological invariant, which is robust against impurity effects. Recent studies on higher-order and fragile topological insulators further demonstrate that the spin-Chern number can exist without gapless edge states. Therefore, the presence of generalized quantum spin-Hall states in real materials can be difficult to identify using only symmetry-based indicators and Wannier obstruction. Such phases require more sophisticated probes of bulk topology. Magnetic flux tube has emerged as one such singular real-space probe that leads to spin-charge separation and allows for a precise diagnosis of the spin-Chern number. In this paper, we develop an automated workflow to scan the database of experimentally relevant, large band-gap, two-dimensional insulators using magnetic flux tubes. The results reveal many material candidates of higher-order topological insulators possessing double spin-Chern number, including the 1H-MX2 family of transition metal dichalcogenides. Our paper has broad implications for current efforts to employ these materials for new platforms of moiré systems.

关键词： Magnetic flux

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Unexpected anisotropic compression-induced superconductivity in pristine 2H-MoTe2

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Physical Review B 2024年第10期110卷 104511页

作者： Tao Lin Run Lv Qing Dong Chenyi Li Bo Liu Ran Liu Xiaoling Jing Yuping Sun Quanjun Li Wenjian Lu Bingbing Liu Key Laboratory of Materials Physics Science Island Branch of Graduate School Institute of Applied Physics Department of Physics and Astronomy HFIPS

High-pressure application is crucial for shaping material properties and revealing novel phenomena. Materials undergo more unpredictable transitions in their crystal and electronic structures under nonhydrostatic/isotropic pressures than under hydrostatic conditions. However, limited knowledge regarding this behavior exists due to a scarcity of relevant studies. In this study, we systematically investigated the evolution of the structure and electronic states of pristine 2H-MoTe2 in anisotropic pressure environments. Surprisingly, we observed anisotropic compression-induced superconductivity in this material, a phenomenon that is absent in quasihydrostatic environments. High-pressure x-ray diffraction and Raman spectroscopy measurements showed no structural phase transitions; however, an anomalous compressive behavior was observed along the c axis. An anisotropic pressure model was proposed based on experimental conditions. First-principles calculations revealed that a strengthened anisotropic compression effect could enhance electron-phonon coupling by increasing the density of states on the Fermi level and softening the phonon modes, contributing to the emergence of superconductivity in 2H-MoTe2. Our findings offer a route for inducing superconductivity, providing insights into the nature of superconductivity in transition metal dichalcogenides and other similar layered compounds under extreme conditions.

关键词： Electrical properties First-principles calculations Phase transitions Pressure effects Superconductivity 2-dimensional systems Superconductors Transition metal dichalcogenides

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Trapping of isotropic droplets by disclinations in nematic liquid crystals controlled by surface anchoring and elastic constant disparity

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Physical Review E 2024年第6期109卷 064703-064703页

作者： Nilanthi P. Haputhanthrige Sathyanarayana Paladugu Maxim O. Lavrentovich Oleg D. Lavrentovich Advanced Materials and Liquid Crystal Institute Department of Physics Department of Earth Environment and Physics Department of Physics and Astronomy Materials Science Graduate Program

Linear defects such as dislocations and disclinations in ordered materials attract foreign particles since they replace strong elastic distortions at the defect cores. In this work, we explore the behavior of isotropic droplets nucleating at singular disclinations in a nematic liquid crystal, predesigned by surface photopatterning. Experiments show that in the biphasic nematic-isotropic region, although the droplets are attracted to the disclination cores, their centers of mass shift away from the core centers as the temperature increases. The shift is not random, being deterministically defined by the surrounding director field. The effect is explained by the balance of interfacial anchoring and bulk elasticity. An agreement with the experiment can be achieved only if the model accounts for the disparity of the nematic elastic constants; the so-called one-constant approximation, often used in the theoretical analysis of liquid crystals, produces qualitatively wrong predictions. In particular, the experimentally observed shift towards the bend region around a +1/2 disclination core can be explained only when the bend constant is larger than the splay constant. The described dependence of the precise location of a foreign inclusion at defect cores on the elastic and surface anchoring properties can be used in rational design of microscale architectures.

关键词： Elastic forces Nucleation Patterning Liquid crystals Nematic liquid crystals Optical microscopy

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Low-temperature spin Seebeck effect in nonmagnetic vanadium dioxide

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Physical Review B 2024年第2期110卷 024415-024415页

作者： Renjie Luo Tanner J. Legvold Liyang Chen Henry Navarro Ali C. Basaran Deshun Hong Changjiang Liu Anand Bhattacharya Ivan K. Schuller Douglas Natelson Department of Physics and Astronomy Applied Physics Graduate Program Rice Quantum Institute Department of Physics and Center for Advanced Nanoscience Materials Science Division Department of Electrical and Computer Engineering Department of Materials Science and NanoEngineering

The spin Seebeck effect (SSE) is sensitive to thermally driven magnetic excitations in magnetic insulators. Vanadium dioxide in its insulating low-temperature phase is expected to lack magnetic degrees of freedom, as vanadium atoms are thought to form singlets upon dimerization of the vanadium chains. Instead, we find a paramagnetic SSE response in VO2 films that grows as the temperature decreases below 50 K. The field and temperature-dependent SSE voltage is qualitatively consistent with a general model of paramagnetic SSE response and inconsistent with triplet spin transport. Quantitative estimates find a spin Seebeck coefficient comparable in magnitude to that observed in strongly magnetic materials. The microscopic nature of the magnetic excitations in VO2 requires further examination.

关键词： Spin Seebeck effect Paramagnets Strongly correlated systems

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Sensing beyond the exceptional point for high detectivity

Sensing beyond the exceptional point for high detectivity

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CLEO: Science and Innovations in CLEO 2024, CLEO: S and I 2024 - Part of Conference on Lasers and Electro-Optics

作者： Li, Zhichao Prasad, Ciril S. Wang, Xielin Zhang, Ding Naik, Gururaj V. Applied Physics Graduate Program Smalley-Curl Institute Rice University HoustonTX77005 United States Department of Electrical and Computer Engineering Rice University HoustonTX77005 United States Department of Physics and Astronomy Rice University HoustonTX77005 United States

Exceptional point (EP)-based optical sensors exhibit exceptional sensitivity but poor detectivity. Slightly off EP operation boosts detectivity without much loss in sensitivity. We experimentally demonstrate a high-detectivity-off-EP plasmonic-photonic hybrid sensor for anti-mouse IgG protein. © Optica Publishing Group 2024

关键词： Hybrid sensors

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Sensing beyond the exceptional point for high detectivity

Sensing beyond the exceptional point for high detectivity

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2024 Conference on Lasers and Electro-Optics, CLEO 2024

ISBN: (纸本)9781957171395

关键词： Laser beams

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Dipolar Weyl semimetals

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Physical Review B 2024年第8期109卷 L081101-L081101页

作者： Alexander C. Tyner Shouvik Sur Graduate Program in Applied Physics Northwestern University Evanston Illinois 60208 USA Department of Physics and Astronomy Rice Center for Quantum Materials Rice University Houston Texas 77005 USA

In Weyl semimetals, Weyl points act as monopoles and antimonopoles of the Berry curvature, with a monopole-antimonopole pair producing a net-zero Berry flux. When inversion symmetry is preserved, the two-dimensional (2D) planes that separate a monopole-antimonopole pair of Weyl points carry quantized Berry flux. In this work, we introduce a class of symmetry-protected Weyl semimetals which host monopole-antimonopole pairs of Weyl points that generate a dipolar Berry flux. Thus, both monopolar and dipolar Berry fluxes coexist in the Brillouin zone, which results in two distinct types of topologically nontrivial planes separating the Weyl points, carrying either a quantized monopolar or a quantized dipolar flux. We construct a topological invariant—the staggered Chern number—to measure the latter, and employ it to topologically distinguish between various Weyl points. Finally, through a minimal two-band model, we investigate physical signatures of bulk topology, including surface Fermi arcs, zero-energy hinge states, and response to insertion of a π-flux vortex.

关键词： Dipolar interaction Symmetry protected topological states Weyl semimetal

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EG32: Unveiling Hidden History: GPR Survey Reveals Buried Water Well in Liluiyah, Khorfakkan's Historic District 7

EG32: Unveiling Hidden History: GPR Survey Reveals Buried Wa...

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7th International Conference on Engineering Geophysics, ICEG 2023

作者： Safa, Khadija Elsamani, Mahmoud A. Khaldi, Hunaida Abdel-Fattah, Mohammed Hamdan, Hamdan University of Sharjah Petroleum Geosciences and Remote Sensing Program Department of Applied Physics and Astronomy United Arab Emirates Sharjah Heritage Institute United Arab Emirates

The Sharjah Institute of Heritage collaborated with the University of Sharjah's Petroleum Geoscience and Remote Sensing program to locate a buried well at a historic heritage site in Liluiyyah, Khorfakkan, United Arab Emirates. The well was an important source of water for the community, and its location was unknown as it had become buried beneath layers of sand and debris. The GPR survey was conducted over almost 600 m2 and more than 375 GPR profiles were obtained. The processed data produced multiple anomalies that were marked and recorded in a Geographic Information System (GIS) database. A group of GPR anomalies was identified in the northern section of the plot, indicating the presence of stones comprising the well mouth. However, after conducting an excavation at the proposed site, the water well was not found. The research team re-evaluated the GPR sections and slices, concentrating on anomalies deeper than 1 m depth and identified a circular shape anomaly at a depth of 15 ns and deeper in the northwestern part of Grid A. A trial pit was executed at the proposed location, revealing the anticipated water well at a depth of 1.2m from the existing ground level. © 2024 7th International Conference on Engineering Geophysics, ICEG 2023. All rights reserved.

关键词： Geophysics

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Laser-enhanced magnetism in SmFeO3

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Physical Review B 2024年第22期109卷 224417-224417页

作者： Mohsen Yarmohammadi Marin Bukov Vadim Oganesyan Michael H. Kolodrubetz Department of Physics Nöthnitzer Str. 38 01187 Dresden Germany Physics Program and Initiative for the Theoretical Sciences The Graduate Center Center for Computational Quantum Physics Department of Physics and Astronomy

We investigate the coherent enhancement of inherently weak magnetic interactions in rare-earth orthoferrite SmFeO3 as a functional material for spintronic applications using a realistic model of dissipative spin dynamics that are linearly and quadratically coupled to laser-driven infrared-active phonons. When linear coupling dominates, we discover a magnetophononic dynamical first-order phase transition in the nonequilibrium steady state which can inhibit strong enhancement of magnetic interactions. By contrast, when quadratic spin-phonon coupling dominates, no phase transition exists at experimentally relevant parameters. By utilizing a chirp protocol, the phase transition can be engineered, enabling stronger magnetic interactions. We also discuss the route for experimental observation of our results.

关键词： Dynamical phase transitions Exchange interaction Magnetic anisotropy Magnetism Optical phonons Spin-phonon coupling Spintronics Ultrafast magnetic effects Ultrafast magnetization dynamics Nonequilibrium systems Rare-earth magnetic materials Chirp Holstein-Primakoff method Lindblad equation Linear spin wave theory Mean field theory Quantum spin chains XYZ model

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