Spin noise of itinerant fermions

TL;DR

This paper develops a theoretical framework for understanding spin noise spectroscopy in noninteracting itinerant fermions, analyzing how temperature, disorder, and magnetic fields influence measurements in different experimental setups.

Contribution

It introduces a comprehensive kinetic equation approach to spin noise in itinerant fermions, clarifying physical interpretations and experimental dependencies.

Findings

Spin noise response scales with system size and light propagation length.

The theory applies to atomic gases and semiconductor conduction electrons.

Provides a baseline for detecting interaction effects in spin noise experiments.

Abstract

We develop a theory of spin noise spectroscopy of itinerant, noninteracting, spin-carrying fermions in different regimes of temperature and disorder. We use kinetic equations for the density matrix in spin variables. We find a general result with a clear physical interpretation, and discuss its dependence on temperature, the size of the system, and applied magnetic field. We consider two classes of experimental probes: 1. electron-spin-resonance (ESR)-type measurements, in which the probe response to a uniform magnetization increases linearly with the volume sampled, and 2. optical Kerr/Faraday rotation-type measurements, in which the probe response to a uniform magnetization increases linearly with the length of the light propagation in the sample, but is independent of the cross section of the light beam. Our theory provides a framework for interpreting recent experiments on atomic gases and conduction electrons in semiconductors and provides a baseline for identifying the effects of interactions on spin noise spectroscopy.