Enhanced Andreev Tunneling via the Kondo Resonance in a Quantum Dot at Finite Bias

TL;DR

This paper investigates nonequilibrium transport in a quantum dot with Coulomb interactions, revealing an anomalous conductance peak at finite bias due to Kondo resonance-assisted Andreev tunneling, which diminishes with temperature.

Contribution

It introduces a novel understanding of finite-bias conductance peaks caused by Kondo resonance in quantum dots coupled to normal and superconducting leads.

Findings

Anomalous conductance peak at finite bias voltage.

Presence of an additional Kondo resonance in local density of states.

Temperature suppresses the Kondo-assisted Andreev tunneling.

Abstract

We study the nonequilibrium transport through a quantum dot coupled to normal and superconducting leads. We use the modified second-order perturbation theory to calculate the differential conductance and the local density of states at the quantum dot. In the strong but finite Coulomb interaction regime, the differential conductance shows an anomalous peak not at a zero bias voltage but at a finite bias voltage. We also observe an additional Kondo resonance besides the normal one in the local density of states, where the former is caused by nonequilibrium Andreev tunneling via the normal Kondo resonance. We explain that this specific Andreev tunneling gives rise to the anomalous peak in the differential conductance. Since the Andreev tunneling via the Kondo resonance is suppressed with increasing temperature, the anomalous peak in the differential conductance disappears at high temperatures.