Stochastic Faraday rotation induced by the electric current fluctuations in nanosystems

TL;DR

This paper presents a theoretical study showing that electron Brownian motion in gyrotropic nanosystems causes stochastic Faraday and Kerr rotation effects, linking optical noise measurements to electronic transport properties.

Contribution

It develops a theory connecting polarization rotation fluctuations to electric current and spin dynamics in various gyrotropic semiconductor systems.

Findings

Fluctuation power spectrum is proportional to ac conductivity.

Electric current, spin, and valley polarization fluctuations contribute to rotation noise.

Optical noise measurements can reveal transport properties of nanosystems.

Abstract

We demonstrate theoretically that in gyrotropic semiconductors and semiconductor nanosystems the Brownian motion of electrons results in temporal fluctuations of the polarization plane of light passing through or reflected from the structure, i.e., in stochastic Faraday or Kerr rotation effects. The theory of the effects is developed for a number of prominent gyrotropic systems such as bulk tellurium, ensembles of chiral carbon nanotubes, and GaAs-based quantum wells of different crystallographic orientations. We show that the power spectrum of these fluctuations in thermal equilibrium is proportional to the ac conductivity of the system. We evaluate contributions resulting from the fluctuations of the electric current, as well as of spin, valley polarization, and the spin current to the noise of the Faraday/Kerr rotation. Hence, all-optical measurements of the Faraday and Kerr rotation noise provide an access to the transport properties of the semiconductor systems.