Shot noise and tunnel magnetoresistance in multilevel quantum dots: Effects of cotunneling

TL;DR

This paper provides a comprehensive theoretical analysis of spin-dependent transport in multilevel quantum dots, highlighting how cotunneling affects tunnel magnetoresistance and shot noise across various bias and gate voltages.

Contribution

It introduces a detailed model incorporating both sequential and cotunneling processes, revealing new effects on TMR suppression and shot noise behavior in Coulomb blockade regions.

Findings

Suppression of TMR due to inelastic cotunneling.

Super-Poissonian shot noise observed in Coulomb blockade regions.

Bias-dependent oscillations of TMR in the sequential tunneling regime.

Abstract

Spin-dependent transport through a multilevel quantum dot weakly coupled to ferromagnetic leads is analyzed theoretically by means of the real-time diagrammatic technique. Both the sequential and cotunneling processes are taken into account, which makes the results on tunnel magnetoresistance (TMR) and shot noise applicable in the whole range of relevant bias and gate voltages. Suppression of the TMR due to inelastic cotunneling and super-Poissonian shot noise have been found in some of the Coulomb blockade regions. Furthermore, in the Coulomb blockade regime there is an additional contribution to the noise due to bunching of cotunneling processes involving the spin-majority electrons. On the other hand, in the sequential tunneling regime TMR oscillates with the bias voltage, while the current noise is generally sub-Poissonian.