Spin-galvanic effect due to optical spin orientation

TL;DR

This paper reports the experimental observation of the spin-galvanic effect in GaAs quantum wells induced by circularly polarized infrared light, supported by a microscopic theory explaining the directional photocurrent differences.

Contribution

It provides the first clear experimental evidence of the spin-galvanic effect under optical excitation in quantum wells and develops a microscopic theory consistent with the observations.

Findings

Helicity-dependent photocurrent observed along <110> axes.

The effect is mainly due to the spin-galvanic effect along one axis.

Theoretical model agrees well with experimental data.

Abstract

Under oblique incidence of circularly polarized infrared radiation the spin-galvanic effect has been unambiguously observed in (001)-grown $n$-type GaAs quantum well (QW) structures in the absence of any external magnetic field. Resonant inter-subband transitions have been obtained making use of the tunability of the free-electron laser FELIX. It is shown that a helicity dependent photocurrent along one of the $<110>$ axes is predominantly contributed by the spin-galvanic effect while that along the perpendicular in-plane axis is mainly due to the circular photogalvanic effect. This strong non-equivalence of the [110] and [1$\bar{1}$0] directions is determined by the interplay between bulk and structural inversion asymmetries. A microscopic theory of the spin-galvanic effect for direct inter-subband optical transitions has been developed being in good agreement with experimental findings.