Spin-polarized current and shot noise in the presence of spin flip in a quantum dot via nonequilibrium Green's functions

TL;DR

This paper investigates how Coulomb interaction, spin-flip processes, and magnetic configurations influence spin-polarized current and shot noise in a quantum dot system using nonequilibrium Green's functions, revealing bias-dependent polarization and noise suppression.

Contribution

It introduces a detailed analysis of spin-polarized transport considering Coulomb interaction and coherent spin-flip, highlighting novel effects on current polarization and shot noise.

Findings

Bias-dependent current polarization in FM-QD-FM systems.

Spin-flip can switch current polarization direction.

Shot noise can be suppressed below 0.5 Fano factor.

Abstract

Using non-equilibrium Green functions we calculate the spin-polarized current and shot noise in a ferromagnet--quantum-dot--ferromagnet (FM-QD-FM) system. Both parallel (P) and antiparallel (AP) magnetic configurations are considered. Coulomb interaction and coherent spin-flip (similar to a transverse magnetic field) are taken into account within the dot. We find that the interplay between Coulomb interaction and spin accumulation in the dot can result in a bias-dependent current polarization $\wp$. In particular, $\wp$ can be suppressed in the P alignment and enhanced in the AP case depending on the bias voltage. The coherent spin-flip can also result in a switch of the current polarization from the emitter to the collector lead. Interestingly, for a particular set of parameters it is possible to have a polarized current in the collector and an unpolarized current in the emitter lead. We also found a suppression of the Fano factor to values well below 0.5.