Mesoscopic fluctuations of spin currents

TL;DR

This paper investigates mesoscopic fluctuations of spin currents in nanostructures, revealing that spin-orbit interactions inherently produce random spin currents with universal amplitude, independent of disorder, and identifies four fluctuation mechanisms.

Contribution

It introduces a general analysis of spin current fluctuations in nanostructures using quantum circuit theory, highlighting four distinct fluctuation mechanisms.

Findings

Spin-orbit interactions generate universal amplitude spin currents.

Disorder does not affect the typical amplitude of these spin currents.

Four mechanisms of spin current fluctuations are identified.

Abstract

Spin currents may be generated by applying bias voltages V to the nanostructures even in the absence of spin-active ferromagnetic interfaces. Most theoretical proposals concentrate on a concrete spin-orbit interaction and on the disorder-averaged effect. It remains underappreciated that any spin-orbit interaction produces random spin currents with a typical amplitude e^2 V/\hbar not affected by disorder. This work addresses such mesoscopic fluctuations of spin currents for generic model of a nanostructure where several quantum connectors meet in a single node. The analysis is performed in the framework of recently developed quantum circuit theory of G_Q corrections and reveals four distinct mechanisms of spin current fluctuations. The results are elaborated for simple models of tunnel and ballistic connectors.