Interplay between interference and Coulomb interaction in the ferromagnetic Anderson model with applied magnetic field

TL;DR

This paper investigates the complex interplay between interference effects and Coulomb interactions in a ferromagnetic Anderson model under magnetic field, comparing various quantum transport methods to understand their accuracy and limitations.

Contribution

It provides a detailed comparison of mean-field, Hubbard-I, and density matrix approaches in modeling quantum transport in a ferromagnetic Anderson system with magnetic field.

Findings

Mean-field approach yields nearly perfect conductance results.

Hubbard-I approximation fails due to breaking hermiticity.

Higher-order density matrix methods reveal features missed by mean-field, like negative differential conductance.

Abstract

We study the competition between interference due to multiple single-particle paths and Coulomb interaction in a simple model of an Anderson-like impurity with local-magnetic-field-induced level splitting coupled to ferromagnetic leads. The model along with its potential experimental relevance in the field of spintronics serves as a nontrivial benchmark system where various quantum transport approaches can be tested and compared. We present results for the linear conductance obtained by a spin-dependent implementation of the density matrix renormalization group scheme which are compared with a mean-field solution as well as a seemingly more advanced Hubbard-I approximation. We explain why mean-field yields nearly perfect results, while the more sophisticated Hubbard-I approach fails, even at a purely conceptual level since it breaks hermiticity of the related density matrix. Furthermore, we study finite bias transport through the impurity by the mean-field approach and recently developed higher-order density matrix equations. We find that the mean-field solution fails to describe the plausible results of the higher-order density matrix approach both quantitatively and qualitatively as it does not capture some essential features of the current-voltage characteristics such as negative differential conductance.