Direct Optical Detection of a Pure Spin Current in Semiconductor

Abstract

We predict that a pure spin current in a semiconductor may induce Faraday birefringence even without magnetization. The theory is based on a derived effective interaction between the spin current and a polarized light beam, where the helicity of a photon is mapped to spin 1/2. The effective coupling between the polarized light beam and electron spin current can be realized in direct-gap semiconductors such as GaAs with inherent spin–orbit coupling in valence bands, but it involves neither the Rashba nor the Dresselhaus effect of samples. We estimate the amplitude of the Faraday rotation due to a pure spin current, and we present its incident-beam-angle dependence. We show that this Faraday birefringence can be directly measured.