Sources of negative tunneling magneto-resistance in multilevel quantum dots with ferromagnetic contacts

TL;DR

This paper investigates how spin-dependent energy level shifts affect tunneling magnetoresistance in multilevel quantum dots with ferromagnetic contacts, highlighting the influence of multiple levels on TMR behavior.

Contribution

It introduces a diagrammatic transport theory to evaluate spin-dependent level shifts in multilevel quantum dots coupled to ferromagnetic leads, applied specifically to carbon nanotube quantum dots.

Findings

Level shifts can be quantitatively evaluated using the proposed diagrammatic approach.

Multiple energy levels can qualitatively alter the TMR effect.

The theory is applicable to complex multilevel quantum dot systems.

Abstract

We analyze distinct sources of spin-dependent energy level shifts and their impact on the tunneling magnetoresistance (TMR) of interacting quantum dots coupled to collinearly polarized ferromagnetic leads. Level shifts due to virtual charge fluctuations can be quantitatively evaluated within a diagrammatic representation of our transport theory. The theory is valid for multilevel quantum dot systems and we exemplarily apply it to carbon nanotube quantum dots, where we show that the presence of many levels can qualitatively influence the TMR effect.