Direct measurement of a pure spin current by a polarized light beam

TL;DR

This paper proposes a method to directly measure pure spin currents in semiconductors using polarized light, exploiting a relativistic interaction that causes circular birefringence without involving magnetic effects.

Contribution

It introduces a novel optical approach to detect pure spin currents via birefringence caused by photon spin interactions, independent of magnetic or inversion asymmetry effects.

Findings

Demonstrates a non-demolition optical measurement technique for pure spin currents.

Establishes a connection between photon helicity and spin current detection.

Shows the effect arises from relativistic spin-orbit coupling in valence bands.

Abstract

The photon helicity may be mapped to a spin-1/2, whereby we put forward an intrinsic interaction between a polarized light beam as a ``photon spin current'' and a pure spin current in a semiconductor, which arises from the spin-orbit coupling in valence bands as a pure relativity effect without involving the Rashba or the Dresselhaus effect due to inversion asymmetries. The interaction leads to circular optical birefringence, which is similar to the Faraday rotation in magneto-optics but nevertheless involve no net magnetization. The birefringence effect provide a direct, non-demolition measurement of pure spin currents.