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arXiv 2021年

作者： Tada, Yasuhiro Quantum Matter Program Graduate School of Advanced Science and Engineering Hiroshima University Hiroshima Higashihiroshima739-8530 Japan

We consider an electron model of superconductivity on a three-dimensional lattice where there are on-site attractive Hubbard interaction and long-range repulsive Coulomb interaction. It is claimed that fully gapped s-wave superconductivity within this model, if present, exhibits spontaneous translation symmetry breaking possibly related to a charge order. Our discussions are based on an application of the Lieb-Schultz-Mattis theorem under some physical assumptions. The inconsistency between the proposed supersolid and experiments can impose some constraints on a reasonable choice of a theoretical model. Copyright © 2021, The Authors. All rights reserved.

关键词： Shear waves

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CSNR Space propulsion optimization code: SPOC

CSNR Space propulsion optimization code: SPOC

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2015 Nuclear and Emerging Technologies for Space, NETS 2015

作者： Husemeyer, Peter J. A. Patel, Vishal Venneri, Paolo F. Deason, Wesley R. Eades, Michael J. Howe, Steven D. Center for Space Nuclear Research Idaho FallsID United States University of Cambridge Cambridgeshire United Kingdom Department of Nuclear Engineering Texas A and M University College StationTX77843 United States Department of Nuclear and Quantum Engineering KAIST Daejeon Korea Republic of Nuclear Engineering Program Ohio State University ColumbusOH43201 United States

ISBN: (纸本)9781510843424

The Low Enriched Uranium (LEU) Nuclear Thermal Rocket (NTR) represents a significant optimization opportunity because of the numerous design parameters that can be adjusted to improve system performance. Performing these optimization studies requires an automated analysis tool that allows for thousands of NTR design iterations to be considered. A code developed by the Center for Space Nuclear Research (CSNR), known as SPOC, brings MCNP, SERPENT and a range of analysis tools together, which makes performing these trade studies substantially faster than was previously possible. In addition to performing rapid analysis, SPOC has unique capabilities which facilitate the optimization of the neutron energy spectrum in a manner that has not previously been discussed in the literature.

关键词： Nuclear energy

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Mechanics of quantum and Sharvin conductors

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Physical Review B 2011年第23期83卷 235422-235422页

作者： Jason N. Armstrong Susan Z. Hua Harsh Deep Chopra Laboratory for Quantum Devices Materials Program Mechanical and Aerospace Engineering Department The State University of New York Buffalo Buffalo New York 14260 USA

Previously, the authors reported direct evidence of channel saturation and conductance quantization in atomic-sized gold constrictions through mechanical perturbation studies, and also showed that peaks in conductance histograms are insufficient in evaluating their mechanical stability [Armstrong et al., Phys. Rev. B 82, 195416 (2010)]. In the present study, gold constrictions spanning the range from quantum to semiclassical (Sharvin) conductance regimes are mechanically probed with picolevel resolution in applied force and deformation, along with simultaneous measurements of conductance. While reconfiguration from one constriction size to another is known to occur by apparently random discrete atomic displacements, results reveal a remarkable simplicity—the magnitude of discrete atomic displacements is limited to a small set of values that correspond to elementary slip distances in gold rather than Au-Au interatomic distance. Combined with measurements of the spring constant of constrictions, results reveal two fundamental crossovers in deformation modes with increasing contact diameter—first, from homogeneous shear to defect-mediated deformation at a diameter that is in close agreement with previous predictions [Sørensen et al., Phys. Rev. B 57, 3283 (1998)]; and second, the discovery of another crossover marking surface- to volume-dominated deformation. A remarkable modulus enhancement is observed when the size of the constrictions approaches the Fermi wavelength of the electrons, and in the limit of a single-atom constriction it is at least two times that for bulk gold. Results provide atomistic insight into the stability of these constrictions and an evolutionary trace of deformation modes, beginning with a single-atom contact.

关键词： PERTURBATION (quantum dynamics) FERMI surfaces WAVELENGTHS ELECTRONIC apparatus & appliances DEFORMATIONS (Mechanics)

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Channel saturation and conductance quantization in single-atom gold constrictions

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Physical Review B 2010年第19期82卷 195416-195416页

作者： Jason N. Armstrong R. M. Schaub Susan Z. Hua Harsh Deep Chopra []Laboratory for Quantum Devices Materials Program Mechanical and Aerospace Engineering Department The State University of New York at Buffalo Buffalo New York 14260 USA

It is shown that the finite elasticity of atomic-sized gold constrictions allows for a continuous and reversible change in conductance. This is achieved by superposition of atomic-scale or subatomic-scale mechanical oscillations on a steadily retracting/approaching gold tip against a gold substrate. Through these perturbation studies, we report the direct observation of channel saturation and conductance quantization in stable, single-atom gold constrictions. In addition, the origin of peaks in conductance histograms is explained, and the peaks alone are shown to be insufficient in evaluating the stability of atomic configurations.

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Antiferromagnetic spin and twin domain walls govern hysteretic expressions of exchange anisotropy

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Physical Review B 2009年第10期80卷 104429-104429页

作者： Jason N. Armstrong Matthew R. Sullivan Harsh Deep Chopra []Laboratory for Quantum Devices Materials Program Mechanical & Aerospace Engineering Department State University of New York at Buffalo Buffalo New York 14260 USA

The present study shows that antiferromagnetic spin and twin domain walls govern the hysteretic expressions of exchange anisotropy at low and high fields, respectively, using annealed NiO single crystals and Co. In the presence of twin walls, spin walls are shown to be a geometrical necessity in the antiferromagnetic NiO. A threshold field (∼10 000 Oe) exists below which twin walls are frozen, and rotational hysteresis is dominated by losses due to spin walls. Above the threshold field, twin walls become mobile, resulting in a sharp increase in rotational hysteresis. Remarkably, rotational hysteresis associated with spin walls is similar to that of an ordinary ferromagnet—as the field strength increases, rotational hysteresis tends toward zero. However, unlike an ordinary ferromagnet where rotational hysteresis becomes zero above its saturation field, rotational hysteresis in antiferromagnet drops but then sharply increases once the threshold field for twin wall motion is exceeded. In crystals without spin walls, low-field rotational hysteresis is zero or negligible. Domain imaging of twin walls in antiferromagnet and Weiss walls in ferromagnet reveals a one-to-one spatial correlation even though twin walls are considered to have no net dipoles. This surprising result is explained by the fact that crystallographic interfaces in real crystals are not atomically sharp or ideal, and the defective interface invariably results in net moment across the finite width of the twin wall. The field dependence of domain walls in Co film exchange coupled to NiO shows global similarities to previously reported behavior of Co films deposited on nanocrystalline NiO [H. D. Chopra, D. X. Yang, P. J. Chen, H. J. Brown, L. J. Swartzendruber, and W. F. Egelhoff, Jr., Phys. Rev. B 61, 15312 (2000)]. In both cases, domain wall motion is not the dominant mode of magnetization reversal (wall motion is entirely absent in the present study while wall motion was only occasionally observed in th

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Robust training of machine learning interatomic potentials with dimensionality reduction and stratified sampling

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npj Computational Materials 2024年第1期10卷 2796-2806页

作者： Ji Qi Tsz Wai Ko Brandon C.Wood Tuan Anh Pham Shyue Ping Ong Materials Science and Engineering Program University of California San Diego9500 Gilman DrLa JollaCA 92093-0448USA Quantum Simulations Group Lawrence Livermore National LaboratoryLivermoreCA 94550USA Department of NanoEngineering University of California San Diego9500 Gilman DrLa JollaCA 92093-0448USA Laboratory for Energy Applications for the Future(LEAF) Lawrence Livermore National LaboratoryLivermoreCA 94550USA

Machine learning interatomic potentials(MLIPs)enable accurate simulations of materials at scales beyond that accessible by ab initio methods and play an increasingly important role in the study and design of ***,MLIPs are only as accurate and robust as the data on which they are ***,we present DImensionality-Reduced Encoded Clusters with sTratified(DIRECT)sampling as an approach to select a robust training set of structures from a large and complex configuration *** applying DIRECT sampling on the Materials Project relaxation trajectories dataset with over one million structures and 89 elements,we develop an improved materials 3-body graph network(M3GNet)universal potential that extrapolates more reliably to unseen *** further show that molecular dynamics(MD)simulations with the M3GNet universal potential can be used instead of expensive ab initioMDto rapidly create a large configuration space for target *** combined this scheme with DIRECT sampling to develop a reliable moment tensor potential for titanium hydrides without the need for iterative augmentation of training *** work paves the way for robust high-throughput development of MLIPs across any compositional complexity.

关键词： stratified potential titanium

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Surface plasmon polaritons at lossy metamaterial-air interfaces

Surface plasmon polaritons at lossy metamaterial-air interfa...

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Signal Processing in Photonic Communications, SPPCom 2016

作者： Sang-Nourpour, Nafiseh Lavoie, Benjamin Kheradmand, R. Sanders, Barry Institute for Quantum Science and Technology University of Calgary Alberta Canada Photonics group Research Institute for Applied Physics and Astronomy University of Tabriz Iran Photonics group Aras International Campus University of Tabriz Iran Department of Electrical and Computer Engineering University of Calgary Alberta Canada Hefei National Laboratory for Physical Sciences at the Microscale University of Science and Technology of China Hefei Anhui China Shanghai Branch CAS Center for Excellence Synergetic Innovation Center in Quantum Information and Quantum Physics University of Science and Technology of China Shanghai China Program in Quantum Information Science Canadian Institute for Advanced Research TorontoON Canada

We derive rigorous criteria for the existence of surface-plasmon polaritons (SPPs) at lossy interfaces by considering properties of SPPs and employing the requirement of causality. These criteria impose limits on susc... 详细信息

ISBN: (纸本)9781943580149

关键词： Photons

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Lieb-Schultz-Mattis Theorem in Higher Dimensions from Approximate Magnetic Translation Symmetry

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Physical Review Letters 2021年第23期127卷 237204-237204页

作者： Yasuhiro Tada Quantum Matter Program Graduate School of Advanced Science and Engineering Hiroshima University Higashihiroshima Hiroshima 739-8530 Japan and Institute for Solid State Physics University of Tokyo Kashiwa 277-8581 Japan

We prove the Lieb-Schultz-Mattis theorem on the energy spectrum of a general two- or three-dimensional quantum many-body system with the U(1) particle number conservation and translation symmetry. Especially, it is demonstrated that the theorem holds in a system with long-range interactions. To this end, we introduce approximate magnetic translation symmetry under the total magnetic flux Φ=2π instead of the exact translation symmetry, and explicitly construct low energy variational states. The energy spectrum at Φ=2π is shown to agree with that at Φ=0 in the thermodynamic limit, which concludes the Lieb-Schultz-Mattis theorem.

关键词： quantum statistical mechanics Equilibrium lattice models Strongly correlated systems Lattice models in condensed matter Symmetries in condensed matter Tight-binding model

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Impurity effects in a one-dimensional spin nematic liquid

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Physical Review B 2024年第10期109卷 104404-104404页

作者： Fumiya Nakamura Yasuhiro Tada Quantum Matter Program Graduate School of Advanced Science and Engineering Hiroshima University Higashihiroshima Hiroshima 739-8530 Japan Institute for Solid State Physics University of Tokyo Kashiwa 277-8581 Japan

We study impurity effects in the spin nematic phase of the S=1/2J1−J2 frustrated spin chain under an external magnetic field by using the infinite density matrix renormalization group and bosonization. It is found that local magnetization almost saturates around the impurity, and the entanglement entropy nearly vanishes at the corresponding bonds, not only when the magnetic interactions near the impurity are weakened but also when they are strengthened compared to those in the bulk. Then we examine spin correlations and Friedel oscillations induced by the impurity. The bosonization provides a qualitative understanding of the characteristic behaviors of the magnetization. We also discuss impacts of the impurity on experiments by focusing on NMR spectra.

关键词： High magnetic fields Magnetic order Magnetism 1-dimensional spin chains Bosonization Spin lattice models Tensor network methods

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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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