Non-universal shot noise in quasiequilibrium spin valves

TL;DR

This paper investigates how electron-electron interactions in diffusive spin valves cause deviations from universal shot noise behavior, revealing configuration-dependent suppression and potential noiseless current in highly polarized systems.

Contribution

It demonstrates the breakdown of the Wiedemann-Franz law's impact on shot noise in spin valves, showing non-universal Fano factors influenced by magnetization alignment and spacer length.

Findings

Universal Fano factor of √3/4 in parallel configuration without spacer.

Spacer length causes non-monotonous suppression of shot noise.

In antiparallel configuration, Fano factor depends on polarization P, approaching zero for P→±1.

Abstract

We show that the breakdown of the Wiedemann-Franz law due to electron--electron scattering in diffusive spin valves may result in a strong suppression of the Fano factor that describes the ratio between shot noise and average current. In the parallel configuration of magnetizations, we find the universal value $\sqrt{3}/4$ in the absence of a normal-metal spacer layer, but including the spacer leads to a non-monotonous suppression of this value before reaching back to the universal value for large spacer lengths. On the other hand, in the case of an antiparallel configuration with a negligibly small spacer, the Fano factor is $\sqrt{3 (1-P^2)}/4$, where $P$ denotes the polarization of the conductivities. For $P\rightarrow \pm 1$, the current through the system is almost noiseless.