Spin-flip scattering in time-dependent transport through a quantum dot: Enhanced spin-current and inverse tunneling magnetoresistance

TL;DR

This paper investigates how spin-flip scattering influences time-dependent transport in a quantum dot, revealing enhanced spin-current and conditions for inverse tunneling magnetoresistance through numerical and analytical methods.

Contribution

It introduces a detailed analysis of spin-flip effects on transient and steady-state transport, including a novel TMR inversion regime and methods to enhance spin-current.

Findings

Transient oscillations damp over different time-scales.

TMR becomes negative when ferromagnetic polarization exceeds a critical value.

Proper tuning of pulsed bias can enhance spin-current.

Abstract

We study the effects of spin-flip scatterings on the time-dependent transport properties through a magnetic quantum dot attached to normal and ferromagnetic leads. The transient spin-dynamics as well as the steady-state tunneling magnetoresistance (TMR) of the system are investigated. The absence of a definite spin quantization axis requires the time-propagation of two-component spinors. We present numerical results in which the electrodes are treated both as one-dimensional tight-binding wires and in the wide-band limit approximation. In the latter case we derive a transparent analytic formula for the spin-resolved current, and transient oscillations damped over different time-scales are identified. We also find a novel regime for the TMR inversion. For any given strength of the spin-flip coupling the TMR becomes negative provided the ferromagnetic polarization is larger than some critical value. Finally we show how the full knowledge of the transient response allows for enhancing the spin-current by properly tuning the period of a pulsed bias.