Understanding the Josephson current through a Kondo-correlated quantum dot

TL;DR

This paper investigates the Josephson current in a Kondo-regime quantum dot using quantum Monte Carlo simulations, revealing how the interplay between Kondo correlations and superconductivity affects the current, with good experimental agreement.

Contribution

It provides a quantitative analysis of the Josephson 0-$ p$ transition in a Kondo quantum dot using numerically exact simulations, including predictions for strong coupling regimes.

Findings

Excellent agreement with experimental critical current dependence.

Identification of the regime where Kondo scale matches the superconducting gap.

Prediction of gate voltage effects on critical current in strong coupling regime.

Abstract

We study the Josephson current 0-$\pi$ transition of a quantum dot tuned to the Kondo regime. The physics can be quantitatively captured by the numerically exact continuous time quantum Monte Carlo method applied to the single-impurity Anderson model with BCS superconducting leads. For a comparison to an experiment the tunnel couplings are determined by fitting the normal-state linear conductance. Excellent agreement for the dependence of the critical Josephson current on the level energy is achieved. For increased tunnel couplings the Kondo scale becomes comparable to the superconducting gap and the regime of the strongest competition between superconductivity and Kondo correlations is reached; we predict the gate voltage dependence of the critical current in this regime.