Magnetoresistance of a quantum dot with spin-active interfaces

TL;DR

This paper investigates how spin-active interfaces influence the magnetoresistance in an interacting quantum dot system, revealing tunable negative and giant MR effects linked to gate voltage and contact properties.

Contribution

It introduces an effective exchange field in an Anderson model to interpret magnetoresistance behavior in quantum dots with spin-active contacts, explaining experimental observations.

Findings

Spin-activity facilitates negative MR effects.

Giant MR effects can be tuned with gate voltage.

Predicted irregular MR oscillations at larger Vg ranges.

Abstract

We study the zero-bias magnetoresistance MR of an interacting quantum dot connected to two ferromagnetic leads and capacitively coupled to a gate voltage source Vg. We investigate the effects of the spin-activity of the contacts between the dot and the leads by introducing an effective exchange field in an Anderson model. This spin-activity makes easier negative MR effects, and can even lead to a giant MR effect with a sign tunable with Vg. Assuming a twofold orbital degeneracy, our approach allows to interpret in an interacting picture the MR(Vg) measured by S. Sahoo et al. [Nature Phys. 2, 99 (2005)] in single wall carbon nanotubes with ferromagnetic contacts. If this experiment is repeated on a larger Vg-range, we expect that the MR(Vg) oscillations are not regular like in the presently available data, due to Coulomb interactions.