pi-Junction behavior and Andreev bound states in Kondo quantum dots with superconducting leads

TL;DR

This paper explores how temperature and coupling affect transport properties and phase transitions in Kondo quantum dots with superconducting leads, revealing the behavior of Andreev bound states and the 0--pi transition.

Contribution

It introduces a combined theoretical approach using SNCA and renormalization group methods to analyze the 0--pi transition and subgap Kondo resonance in superconducting quantum dots.

Findings

The phase diagram of the 0--pi transition is mapped out.

Conductance approaches zero at low temperatures.

Finite temperature modifies the 0--pi transition characteristics.

Abstract

We investigate the temperature- and coupling-dependent transport through Kondo dot contacts with symmetric superconducting s-wave leads. For finite temperature T we use a superconducting extension of a selfconsistent auxiliary boson scheme, termed SNCA, while at T=0 a perturbative renormalization group treatment is applied. The finite-temperature phase diagram for the 0--pi transition of the Josephson current in the junction is established and related to the phase-dependent position of the subgap Kondo resonance with respect to the Fermi energy. The conductance of the contact is evaluated in the zero-bias limit. It approaches zero in the low-temperature regime, however, at finite T its characteristics are changed through the coupling- and temperature-dependent 0--pi transition.