arXiv subjects

Paul Wenk

Publications and source records attributed to Paul Wenk.

21 records · Page 2Linked to original sources

arXiv2012

Spin Hall Conductivity on the Anisotropic Triangular Lattice

We present a detailed study of the spin Hall conductivity on a two-dimensional triangular lattice in the presence of Rashba spin-orbit coupling. In particular, we focus part of our attention on the effect of the anisotropy of the nearest neighbor hopping amplitude. It is found that the presence of anisotropy has drastic effects on the spin Hall conductivity, especially in the hole doped regime where a significant increase or/and reversed sign of the spin Hall conductivity has been obtained. We also provide a systematic analysis of the numerical results in terms of Berry phases. The changes of signs observed at particular density of carriers appear to be a consequence of both Fermi surface topology and change of sign of electron velocity. In addition, in contrast to the two-dimensional square lattice, it is shown that the tight binding spin-orbit Hamiltonian should be derived carefully from the continuous model on the triangular lattice.

cond-mat.mes-hall↗

arXiv2010

Spin Relaxation in Quantum Wires

The spin dynamics and spin relaxation of itinerant electrons in quantum wires with spin-orbit coupling is reviewed. We give an introduction to spin dynamics, and review spin-orbit coupling mechanisms in semiconductors. The spin diffusion equation with spin-orbit coupling is derived, using only intuitive, classical random walk arguments. We give an overview of all spin relaxation mechanisms, with particular emphasis on the motional narrowing mechanism in disordered conductors, the D'yakonov-Perel'-Spin relaxation. Here, we discuss in particular, the existence of persistent spin helix solutions of the spin diffusion equation, with vanishing spin relaxation rates. We then, derive solutions of the spin diffusion equation in quantum wires, and show that there is an effective alignment of the spin-orbit field in wires whose width is smaller than the spin precession length $L_{\rm SO}$. We show that the resulting reduction in the spin relaxation rate results in a change in the sign of the quantum corrections to the conductivity. Finally, we present recent experimental results which confirm the decrease of the spin relaxation rate in wires whose width is smaller than $L_{\rm SO}$: the direct optical measurement of the spin relaxation rate, as well as transport measurements, which show a dimensional crossover from weak antilocalization to weak localization as the wire width is reduced. Open problems remain, in particular in narrower, ballistic wires, were optical and transport measurements seem to find opposite behavior of the spin relaxation rate: enhancement, suppression, respectively. We conclude with a review of these and other open problems which still challenge the theoretical understanding and modeling of the experimental results.

cond-mat.mes-hall↗

arXiv2010

Direction Dependence of Spin Relaxation in Confined 2D Systems

The dependence of spin relaxation on the direction of the quantum wire under Rashba and Dresselhaus (linear and cubic) spin orbit coupling is studied. Comprising the dimensional reduction of the wire in the diffusive regime, the lowest spin relaxation and dephasing rates for (001) and (110) systems are found. The analysis of spin relaxation reduction is then extended to non-diffusive wires where it is shown that, in contrast to the theory of dimensional crossover from weak localization to weak antilocalization in diffusive wires, the relaxation due to cubic Dresselhaus spin orbit coupling is reduced and the linear part shifted with the number of transverse channels.

cond-mat.dis-nn↗