Spin-current noise from fluctuation relations

TL;DR

This paper derives fluctuation relations linking spin current and noise in mesoscopic conductors, extending the fluctuation-dissipation theorem to nonlinear regimes and systems with magnetic fields or ferromagnetic contacts.

Contribution

It introduces fluctuation relations for spin currents that connect nonlinear conductance, noise susceptibility, and higher cumulants, applicable to magnetic and ferromagnetic systems.

Findings

Fluctuation relations reduce to the fluctuation-dissipation theorem in linear response.

New relations connect nonlinear spin conductance with noise and higher cumulants.

Results hold even with magnetic fields and ferromagnetic electrodes.

Abstract

We present fluctuation relations that connect spin-polarized current and noise in mesoscopic conductors. In linear response, these relations are equivalent to the fluctuation-dissipation theorem that relates equilibrium current--current correlations to the linear conductance. More interestingly, in the weakly nonlinear regime of transport, these relations establish a connection between the leading-order rectification spin conductance, the spin noise susceptibility and the third cumulant of spin current fluctuations at equilibrium. Our results are valid even for systems in the presence of magnetic fields and coupled to ferromagnetic electrodes.