Renormalization effects in interacting quantum dots coupled to superconducting leads

David Futterer, Jacek Swiebodzinski, Michele Governale, Jürgen König

Published 2012-10-08, updated 2013-01-18Version 2

We study subgap transport through an interacting quantum dot tunnel coupled to one normal and two superconducting leads. To check the reliability of an approximation of an infinitely-large gap $\Delta$ in the superconducting leads and weak tunnel coupling to the normal lead, we perform a $1/\Delta$ expansion, and we analyze next-to-leading order corrections in the tunnel coupling to the normal lead. Furthermore, we propose a resummation approach to calculate the Andreev bound states for finite $\Delta$. The results are substantially more accurate than those obtained by mean-field treatments and favorably compare with numerical exact results.