Spin polarized transport driven by square voltage pulses in a quantum dot system

TL;DR

This paper investigates spin-polarized transport in a quantum dot system driven by square voltage pulses, revealing dynamic spin accumulation, TMR spikes, and sign changes due to ultrafast bias switching.

Contribution

It introduces a time-dependent nonequilibrium Green function approach to analyze spin transport under pulsed bias in quantum dots with ferromagnetic leads.

Findings

Spin accumulation and spin current can change sign over time.

TMR exhibits spikes and sign reversals during bias pulses.

Ultrafast bias switching causes rapid current reversals.

Abstract

We calculate current, spin current and tunnel magnetoresistance (TMR) for a quantum dot coupled to ferromagnetic leads in the presence of a square wave of bias voltage. Our results are obtained via time-dependent nonequilibrium Green function. Both parallel and antiparallel lead magnetization alignments are considered. The main findings include a wave of spin accumulation and spin current that can change sign as the time evolves, spikes in the TMR signal and a TMR sign change due to an ultrafast switch from forward to reverse current in the emitter lead.