A Simple Perturbation Theory of a Quantum Dot Coupled to Superconducting Leads

Abstract

The transport in a superconductor-quantum-dot-superconductor system is studied analytically using a simple perturbation theory. The dc Josephson current through a quantum dot depends on the phase difference and the binding energy of the localized excited states, is not always a sine curve and is also influenced greatly by the competition between the superconductivity and the Kondo effect. π junction is shown analytically.