AC Josephson transport through interacting quantum dots

TL;DR

This paper studies the AC Josephson current through an interacting quantum dot connected to superconducting and normal leads, using a diagrammatic real-time approach to analyze the effects of Coulomb interactions and bias voltages.

Contribution

It introduces a perturbative diagrammatic method to analyze AC Josephson transport in strongly interacting quantum dots with multiple leads.

Findings

AC current depends on quantum dot level and charging energy

Proximity effect induces superconducting correlations on the dot

Bias voltages influence the AC Josephson signal

Abstract

We investigate the AC Josephson current through a quantum dot with strong Coulomb interaction attached to two superconducting and one normal lead. To this end, we perform a perturbation expansion in the tunneling couplings within a diagrammatic real-time technique. The AC Josephson current is connected to the reduced density matrix elements that describe superconducting correlations induced on the quantum dot via proximity effect. We analyze the dependence of the AC signal on the level position of the quantum dot, the charging energy, and the applied bias voltages.