Vendredi 05 juillet 2013 à 15h45
Auditoire Stueckelberg, Ecole de Physique

Nonequilibrium transport measurement of Andreev bound states near the 0-pi transition in a superconductor-carbon nanotube-superconductor junction

Rosa Lopez, University of the Balearic Islands, Spain

We report non-equilibrium transport measurement of gate tunable Andreev bound states in a nanotube quantum dot coupled to two superconducting leads [1]. In particular, we observe clear features of the two different types of Kondo ridges, which can be understood in terms of the interplay between the Kondo effect and the superconductivity. In the first type of the Kondo ridge (Type I), the coupling is strong and the Kondo effect is dominant. The levels of the Andreev bound states display anti-crossing in the middle of the ridge. On the other hand, crossing of the two Andreev bound states is shown in the second type of the Kondo ridge (type II), which is directly related to the $0-?$ transition of the Josephson junction. Our scenario is well understood in terms of only a single dimensionless parameter, $k_B T_K^{min}/ Delta$, where $T_K^{min}$ and $Delta$ are the minimum Kondo temperature of a ridge and the superconducting order parameter, respectively. Our observation is also confirmed by the numerical renormalization group calculation. Bum-Kyu Kim, et al Phys. Rev. Lett. 110, 076803 (2013).