Quantum Dot in the Kondo Regime coupled to p-wave superconductors

Abstract

This paper studies the physics of junctions containing superconducting $(S)$ and normal $(N)$ leads weakly coupled to an Anderson impurity in the Kondo regime $(K)$. Special attention is devoted to the case where one of the leads is a $p-wave$ superconductor where mid-gap surface states play an important role in the tunneling processes and help the formation of Kondo resonance. The novel physics in these systems beyond that encountered in quantum dots coupled only to to normal leads is that electron transport at finite bias $eV$ in $SKN$ and $SKS$ junctions is governed by Andreev reflections. These enable the occurrence of dissipative current even when the bias $eV$ is smaller than the superconducting gap $Δ$. Using the slave boson mean field approximation the current, shot-noise power and Fano factor are calculated as functions of the applied bias voltage in the sub-gap region $eV < Δ$ and found to be strongly dependent on the ratio $t_K$ between the Kondo temperature $T_{K}$ and the superconducting gap $Δ$. In particular, for large values of $t_K$ the attenuation of current due to the existence of the superconducting gap is compensated by the Kondo effect. This scenario is manifested also in the behavior of the Josephson current as function of temperature.