Current fluctuations in a spin filter with paramagnetic impurities

TL;DR

This paper investigates how frequency-dependent shot noise in a spin filter is influenced by spin-flip scattering from magnetic impurities, revealing a link to the Korringa relaxation rate under nonequilibrium conditions.

Contribution

It introduces a detailed analysis of frequency-dependent shot noise caused by magnetic impurities in a spin filter, highlighting the role of the Korringa relaxation rate.

Findings

Frequency-dependent noise is driven by spin-flip scattering from magnetic impurities.

The noise dispersion occurs at frequencies near the Korringa relaxation rate.

The relaxation rate scales with applied bias voltage under nonequilibrium conditions.

Abstract

We analyze the frequency dependence of shot noise in a spin filter consisting of a normal grain and ferromagnetic electrodes separated by tunnel barriers. The source of frequency-dependent noise is random spin-flip electron scattering that results from spin-orbit interaction and magnetic impurities. Though the latter mechanism does not contribute to the average current, it contributes to the noise and leads to its dispersion at frequencies of the order of the Korringa relaxation rate. Under nonequilibrium conditions, this rate is proportional to the applied bias $V$, but parametrically smaller than $eV/\hbar$.