Josephson Current in Strongly Correlated Double Quantum Dots

Abstract

We study the Josephson current through a serial double quantum dot and the associated 0 - pi transitions which result from the subtle interplay between the superconductivity, the Kondo physics, and the interdot superexchange interaction. The competition between them is examined by tuning the relative strength Delta/T(K) of the superconducting gap and the Kondo temperature, for different strengths of the superexchange coupling determined by the interdot tunneling t relative to the level broadening Gamma. We find strong renormalization of t, a significant role of the superexchange coupling J, and a rich phase diagram of the 0 and pi-junction regimes. In particular, when both the superconductivity and the exchange interaction compete with the Kondo physics (Delta similar to J similar to T(K)), there appears an island of pi' phase at large values of the superconducting phase difference.