arXiv subjects

Guang-Yu Guo

Publications and source records attributed to Guang-Yu Guo.

95 records · Page 6Linked to original sources

arXiv2009

Transverse force generated by an electric field and transverse charge imbalance in spin-orbit coupled systems

We use linear response theory to study the transverse force generated by an external electric field and hence possible charge Hall effect in spin-orbit coupled systems. In addition to the Lorentz force that is parallel to the electric field, we find that the transverse force perpendicular to the applied electric field may not vanish in a system with an anisotropic energy dispersion. Surprisingly, in contrast to the previous results, the transverse force generated by the electric field does not depend on the spin current, but in general, it is related to the second derivative of energy dispersion only. Furthermore, we find that the transverse force does not vanish in the Rashba-Dresselhaus system. Therefore, the non-vanishing transverse force acts as a driving force and results in charge imbalance at the edges of the sample. The estimated ratio of the Hall voltage to the longitudinal voltage is $\sim 10^{-3}$. The disorder effect is also considered in the study of the Rashba-Dresselhaus system. We find that the transverse force vanishes in the presence of impurities in this system because the vertex correction and the anomalous velocity of the electron accidently cancel each other.

cond-mat.mes-hall↗

arXiv2009

Tuning linear and nonlinear optical properties of wurtzite GaN by c-axial stress

We study the linear and nonlinear optical properties of wurtzite GaN under c-axial stress field, using density functional theory calculations. The fully structural optimization at each c-axial strain was performed. The calculated dielectric functions show that tensile c-axial strain effectively improves the linear optical efficiency, especially for the band-edge transitions, and significantly increase the mobility of electrons in the conduction band. Second-order nonlinear optical susceptibilities show that the tensile c-axial strain will enhance the zero- and low-frequency nonlinear responses of GaN. The enhancement of the nonlinear optical property is explained by the reduction of the polarization of wurtzite GaN under tensile c-axial strains. Based on these findings, we propose a method for improving the electrical and optical properties of the crystal through imposing appropriate stress on the high symmetry crystalline directions.

physics.comp-ph↗

arXiv2009

Microscopic origin of light emission in Al_yGa_{1-y}N/GaN superlattice: Band profile and active site

We present first-principles calculations of AlGaN/GaN superlattice, clarifying the microscopic origin of the light emission and revealing the effect of local polarization within the quantum well. Profile of energy band and distributions of electrons and holes demonstrate the existence of a main active site in the well responsible for the main band-edge light emission. This site appears at the position where the local polarization becomes zero. With charge injection, the calculated optical spectra show that the broadening of the band gap at the active site leads to the blueshift of emission wavelength.

physics.comp-ph↗

arXiv2009

Torque and conventional spin-Hall currents in two-dimensional spin-orbit coupled systems: Universal relation and hyper-selection rule

We investigate torque and also conventionally defined spin-Hall currents in two-dimensional (2D) spin-orbit coupled systems of spin-1/2 particles within the linear response Kubo formalism. We obtain some interesting relations between the conventional and torque spin-Hall conductivities for the generic effective Hamiltonian $H_0=ε_k^0+A(k)σ_x-B(k)σ_y$, where $A(k)=η^A_ik_i+η^A_{ij}k_ik_j+η^A_{ijl}k_ik_jk_l+...$, $B(k)=η^B_ik_i+η^B_{ij}k_ik_j+η^B_{ijl}k_ik_jk_l+...$, and $η$'s are the specific system-dependent coefficients. Specifically, we find that in the intrinsic case the magnitude of torque spin-Hall conductivity $σ^{τ_z}_{xy}(0)$ is always twice larger than the conventional spin-Hall conductivity $σ^{s_z}_{xy}(0)$, and the two conductivities have the opposite signs, i.e., $σ^{τ_z}_{xy}(0)=-2σ^{s_z}_{xy}(0)$. This universal relation also holds in the presence of an uniform in-plane magnetic field. We also find that if the energy dispersion is rotationally invariant, there exists a hyper-angular momentum $I_z = (k\times \partialθ/\partial k)_z s_z + L_z$ which is conserved. Furthermore, the hyper-angular momentum current $<{1/2}\{I_z,v_x\}>$ vanishes, and this leads to a hyper selection rule for the conventional spin-Hall current.

cond-mat.mes-hall↗

arXiv2008

Enhanced spin Hall effect by resonant skew scattering in orbital-selective Kondo effect

The enhanced spin Hall effect in Au metal due to the resonant skew scattering is studied with first-principles band structure calculations. Especially the gigantic spin Hall angle $γ_S \cong 0.1$ observed recently (T.Seki et al., Nature Materials {\bf 7}, 125 (2008)) is attributed to the orbital-dependent Kondo effect of Fe in the Au host metal, where the $t_{2g}$-orbitals are in the mixed-valence region while $e_g$-orbitals are in the Kondo limit. The enhanced spin-orbit interaction by the electron correlation in the $t_{2g}$-orbitals leads to the gigantic spin Hall effect. Impurities with 5d orbitals are also discussed.

cond-mat.str-el↗