Universality in higher order spin noise spectroscopy

TL;DR

This paper proposes a universal phenomenological framework for higher order spin noise correlators, revealing their dependence on fundamental parameters and constraints from fluctuation theorems, with microscopic examples for conduction electrons.

Contribution

It introduces a universal description of third and fourth order spin cumulants based on a small set of parameters and fluctuation theorem constraints.

Findings

Third and fourth order spin cumulants are universally described by a small parameter set.

Fluctuation theorem constrains the form of higher order spin correlators.

Microscopic calculations for conduction electrons support the phenomenological approach.

Abstract

Higher order time-correlators of spontaneous spin fluctuations reveal the information about spin interactions. We argue that in a broad class of spin systems one can justify a phenomenological approach to explore such correlators. Thus, we predict that the 3rd and 4th order spin cumulants are described by a universal function that can be parametrized by a small set of parameters. We show that the fluctuation theorem constrains this function so that such correlators are fully determined by lowest nonlinear corrections to the free energy and the mean and variance of microscopic spin currents. We also provide an example of microscopic calculations for conduction electrons.