Spin-polarized current generation from quantum dots without magnetic fields

Abstract

An unpolarized charge current passing through a chaotic quantum dot with spin-orbit coupling can produce a spin-polarized exit current without magnetic fields or ferromagnets. We use random matrix theory to estimate the typical spin polarization as a function of the number of channels in each lead in the limit of large spin-orbit coupling. We find rms spin polarizations up to 45% with one input channel and two output channels. Finite temperature and dephasing both suppress the effect, and we include dephasing effects using a variation of the third lead model. If there is only one channel in the output lead, no spin polarization can be produced, but we show that dephasing lifts this restriction.

Generation and Detection of Spin Currents in Semiconductor Nanostructures with Strong Spin-Orbit Interaction

“…This Letter reports two major advances of nanoscale semiconductor spintronics. Namely, we develop novel experimental methods to electrically generate and quantitatively measure spin currents in a two-dimensional semiconductor nanostructure.It is predicted that charge currents flowing through spin-orbit interaction (SOI)-coupled nanostructures are generically accompanied by spin currents, if the spinorbit time is shorter than the electron dwell time [9][10][11][12]. This spin current generation mechanism is purely electrical and based on the mesoscopic SHE (MSHE) [9,10], where the electronic orbital dynamics in chaotic nanostructures cooperates with the SOI to make transport spin dependent.…”

Generalized correlation functions for conductance fluctuations and the mesoscopic spin Hall effect

“…6 Signals of the spin accumulation can be inferred, for instance, from time-dependent fluctuations of the spectral currents (noise power) 10 or from the analysis of universal conductance fluctuations. [11][12][13][14] Spin Hall conductance fluctuations have been theoretically studied for mesoscopic systems in the diffusive 11 as well as in the ballistic regime. 12 In the absence of both spin rotation symmetry and magnetic field, these studies predict universal spin Hall conductance fluctuations with a root-mean-square amplitude of about 0.18(e/4π ).…”

Scattering theory of current-induced spin polarization

“…In other words, RMT predicts that only accumulations right at the boundary of the sample can be extracted and converted into spin currents in the linear regime, which is consistant with the universal fluctuations of spin currents found in Refs. [16][17][18][19]. It is at present unclear if more spin current can be extracted in nonlinear regimes of transport.…”

“…These quasiclassical theories have been quite successful, however they neglect coherent effects and, in their present form, are not appropriate to investigate local fluctuations and spatial correlations of spin polarization. Coherent mesoscopic effects on spin currents have recently attracted quite some theoretical attention, both analytically [15][16][17][18][19][20] and numerically [21,22], in both diffusive and ballistic systems, while so far only mesoscopic fluctuations of sample-integrated spin polarizations in the diffusive regime have been investigated [23]. At present, little is known about local coherent fluctuations of spin polarizations, the scale on which they occur, how they are correlated, and how they influence spin currents and their fluctuations, neither have current-induced spin polarizations in chaotic ballistic systems been investigated so far.…”