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排序方式: 共有569条查询结果,搜索用时 109 毫秒
561.
Vertex correction of the anisotropic magnetic impurities to the spin polarization of 2D electron gas
L. Ren 《Physics letters. A》2008,372(23):4307-4310
In terms of Kubo's formula and Green's function method, for the two-dimensional electron gas (2DEG) with Rashba spin-orbit coupling (SOC), we study the spin polarization due to the effect from magnetic impurities with anisotropic spin dependent delta type coupling to electrons when an external dc electric field in plane is applied. The vertex correction of impurities in ladder approximation is carried out in the limit of EF?1/τ, Δ. We find that the strength of spin polarization can be significantly modified by vertex correction and the spin polarization is relevant to the anisotropy coefficient γ, but the direction of net spin polarization cannot be changed. 相似文献
562.
Lattice constants, elasticity, band structure and piezoelectricity of hexagonal wide band gap BexZn1−xO ternary alloys are calculated using first-principles methods. The alloys' lattice constants obey Vegard's law well. As Be concentration increases, the bulk modulus and Young's modulus of the alloys increase, whereas the piezoelectricity decreases. We predict that BexZn1−xO/GaN/substrate (x=0.022) multilayer structure can be suitable for high-frequency surface acoustic wave device applications. Our calculated results are in good agreement with experimental data and other theoretical calculations. 相似文献
563.
Using the time-dependent Schrödinger equation, we present the analytical result of the expectation value of spin injected into a two-dimensional electron gas with respect to an arbitrarily spin-polarized electron state and monitor the spin time-evolution. We demonstrate that the expectation value of spin operator Sx is the time-independent, and only the expectation values in the Sy-Sz plane are time-dependent. A detailed study of spin precession in the spin-valve and spin-transistor geometry is presented, in which the initial spin-polarized electron state point perpendicular and parallel to the current direction, respectively. We put forward the possible reason that the resistance change is independent of gate voltage in the spin-valve geometry. Furthermore, it has been shown that the effective magnetic field generated by the spin-orbit interaction is not same with the truly magnetic field. The main effect of the truly magnetic field is to align the spin along the field direction, but the effective magnetic field generated by the spin-orbit interaction does not. 相似文献
564.
A. Bouhemadou 《Physica B: Condensed Matter》2008,403(17):2707-2713
Using first-principles calculations, we have studied the structural and elastic properties of M2SnC, with M=Ti, Zr, Nb and Hf. Geometrical optimization of the unit cell is in good agreement with the available experimental data. The effect of high pressures, up to 20 GPa, on the lattice constants shows that the contractions along the a-axis were higher than those along the c-axis. We have observed a quadratic dependence of the lattice parameters versus the applied pressure. The elastic constants and their pressure dependence are calculated using the static finite strain technique. A linear dependence of the elastic stiffnesses on the pressure is found. We derived the bulk and shear moduli, Young's moduli and Poisson's ratio for ideal polycrystalline M2SnC aggregates. We estimated the Debye temperature of M2SnC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of Ti2SnC, Zr2SnC, Nb2SnC, and Hf2SnC compounds. 相似文献
565.
In this work we analyze the spin-polarized charge density distribution in the GeMn diluted ferromagnetic semiconductors (DFS). The calculations are performed within a self-consistent k·p method, in which the exchange correlation effects in the local density approximation, as well as the strain effects due to the lattice mismatch, are taken into account. Our findings show that the extra confinement potential provided by the barriers and the variation of the Mn content in the DFS are responsible for a separation between the different spin charge densities, giving rise to higher mobility spin-polarized currents or high ferromagnetism transition temperatures systems. 相似文献
566.
567.
Jean-Baptiste Leblond Djimédo Kondo Léo Morin Almahdi Remmal 《Comptes Rendus Mecanique》2018,346(4):336-349
Classical limit analysis applies to ideal plastic materials, and within a linearized geometrical framework implying small displacements and strains. Sequential limit analysis was proposed as a heuristic extension to materials exhibiting strain hardening, and within a fully general geometrical framework involving large displacements and strains. The purpose of this paper is to study and clearly state the precise conditions permitting such an extension. This is done by comparing the evolution equations of the full elastic–plastic problem, the equations of classical limit analysis, and those of sequential limit analysis. The main conclusion is that, whereas classical limit analysis applies to materials exhibiting elasticity – in the absence of hardening and within a linearized geometrical framework –, sequential limit analysis, to be applicable, strictly prohibits the presence of elasticity – although it tolerates strain hardening and large displacements and strains. For a given mechanical situation, the relevance of sequential limit analysis therefore essentially depends upon the importance of the elastic–plastic coupling in the specific case considered. 相似文献
568.
Weinan E~* Jianfeng LU~ 《数学年刊B辑(英文版)》2007,28(6):665-676
The authors consider the simplest quantum mechanics model of solids,the tight binding model,and prove that in the continuum limit,the energy of tight binding model converges to that of the continuum elasticity model obtained using Cauchy-Born rule.The technique in this paper is based mainly on spectral perturbation theory for large matrices. 相似文献
569.
Distance Between Unitary Orbits of Self-AdjointElements in C*-Algebras of Tracial Rank One 下载免费PDF全文
Ruofei WANG 《数学年刊B辑(英文版)》2023,44(3):407-444
The note studies certain distance between unitary orbits. A result about Riesz interpolation property is proved in the first place. Weyl (1912) shows that dist(U(x), U(y)) = δ(x, y) for self-adjoint elements in matrixes. The author generalizes the result to C*-algebras of tracial rank one. It is proved that dist(U(x), U(y)) = Dc(x, y) in unital AT -algebras and in unital simple C*-algebras of tracial rank one, where x, y are self-adjoint elements and Dc (x, y) is a notion generalized from δ(x, y). 相似文献