Andreev bound states and Josephson coupling in YBa$_2$Cu$_3$O$_7$/Pb tunnel junctions
Abstract
We have made in-situ [103] and [110]YBCO/Pb junctions, which display an hysteretic behaviour with both a well-defined Quasi-Particule branch and a Josephson current. A zero energy conductance peak is observed in the tunneling conductance — which is a signature of Andreev Bound States (ABS) at a surface of a d-wave superconductor — which splits at low temperature. This may confirm the existence of a surface state which breaks time-reversal symmetry. However, up to now, we have not seen any evidence of a coupling between Josephson current and the zero-energy ABS, predicted by Y. Tanaka and S. Kashiwaya 1