Nonequilibrium spintronic transport through Kondo impurities

TL;DR

This paper investigates the nonequilibrium spin-dependent transport through quantum impurities like quantum dots or molecules attached to ferromagnetic leads, revealing how the Kondo resonance is affected by bias, spin polarization, magnetic fields, and temperature.

Contribution

It introduces a hybrid numerical approach combining NRG and tDMRG to accurately analyze spin-resolved transport in nonequilibrium Kondo systems with ferromagnetic leads.

Findings

Kondo resonance appears as a zero-bias peak in differential conductance.

Spin polarization reduces the Kondo resonance due to an induced exchange field.

Applying a magnetic field can restore the Kondo resonance affected by spin polarization.

Abstract

In this work we analyze the nonequilibrium transport through a quantum impurity (quantum dot or molecule) attached to ferromagnetic leads by using a hybrid numerical renormalization group-time-dependent density matrix renormalization group thermofield quench approach.For this, we study the bias dependence of the differential conductance through the system, which shows a finite zero-bias peak, characteristic of the Kondo resonance and reminiscent of the equilibrium local density of states. In the non-equilibrium settings, the resonance in the differential conductance is also found to decrease with increasing the lead spin polarization. The latter induces an effective exchange field that lifts the spin degeneracy of the dot level. Therefore as we demonstrate, the Kondo resonance can be restored by counteracting the exchange field with a finite external magnetic field applied to the system. Finally, we investigate the influence of temperature on the nonequilibrium conductance, focusing on the split Kondo resonance. Our work thus provides an accurate quantitative description of the spin-resolved transport properties relevant for quantum dots and molecules embedded in magnetic tunnel junctions.