Josephson current in a quantum dot in the Kondo regime connected to two superconductors

We apply a Gutzwiller-like variational technique to study Josephson conduction across a quantum dot with an odd number of electrons connected to two superconducting leads. Our method projects out all states on the dot but the Kondo singlet and is valid when Kondo correlations are dominant and no Andreev bound states localized at the dot are available for Kondo screening. In these conditions superconducting pairing is a competing effect and the junction is pi-like, to optimize antiferromagnetic correlations on the dot. As the superconducting gap increases, the Josephson current also increases, but its phase dependence becomes strongly non-sinusoidal. (C) 2004 Elsevier B.V. All rights reserved.