Superconducting non-equilibrium transport through a weakly interacting   quantum dot
  We study the out-of-equilibrium current through an interacting quantum dot modelled as an Anderson impurity contacted by two BCS superconductors held at fixed voltage bias. In order to account for multiple Andreev reflections, we develop a Keldysh Green's function scheme perturbative in the dot's interaction strength. We find an unexpected enhancement of the current due to repulsive interactions for small lead-to-dot couplings. 
L. Dell'Anna, A. Zazunov, and R. Egger