Kondo-type transport through an interacting quantum dot coupled to ferromagnetic leads

TL;DR

This paper explores how the Kondo effect manifests in a quantum dot connected to ferromagnetic leads, revealing how spin alignment influences the density of states and conductance, with potential applications in spintronics.

Contribution

It provides a detailed analysis of the Kondo effect in quantum dots with ferromagnetic leads for different spin configurations using the non-crossing approximation.

Findings

Anti-parallel alignment shows a single Kondo peak with conventional temperature behavior.

Parallel alignment causes the Kondo peak to split into two, creating a valley and a hump in conductance.

Bias voltage can split Kondo peaks in nonequilibrium conditions.

Abstract

We investigate the equilibrium and out-of-equilibrium Kondo effects in a single-level interacting quantum dot connected to two ferromagnetic leads. Within the non-crossing approximation, we calculate the total density of states (DOS), the linear conductance, and the nonlinear differential conductance for both the parallel and the anti-parallel alignments of the spin polarization orientation in the leads, followed by a brief discussion regarding the validity of this approach. Numerical calculations show that for the anti-parallel alignment, a single Kondo peak always appears in the equilibrium DOS, resulting in the conventional temperature behavior in the linear conductance and the zero-bias maximum in the differential conductance. The strength of the DOS peak is gradually suppressed with increasing polarization, due to the fact that formation of the Kondo-correlated state is more difficult in the presence of higher polarization. On the contrary, for the parallel configuration the Kondo peak in the DOS descends precipitately and splits into two peaks to form a very steep valley between them. This splitting contributes to the appearance of a "hump" in the temperature-dependent linear conductance and a nonzero-bias maximum in the differential conductance. Moreover, application of a bias voltage can split each Kondo peak into two in the nonequilibrium DOS for both configurations. Finally we point out that the tunnel magnetoresistance could be an effective tool to demonstrate the different Kondo effects in different spin configurations found here.