Andreev Bound States and Josephson Coupling in YBCO/Pb tunnel junction

TL;DR

This study investigates YBCO/Pb tunnel junctions revealing Andreev Bound States and Josephson effects, with observations of surface states and conductance peaks, but no coupling between Josephson current and ABS.

Contribution

The paper reports in-situ YBCO/Pb junctions exhibiting Andreev Bound States and Josephson effects, and explores surface states breaking time-reversal symmetry.

Findings

Zero energy conductance peak observed

Splitting of peak at low temperature suggests surface state

No evidence of coupling between Josephson current and ABS

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. The observed splitting of this peak at low temperature 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 (PRB 56 p.892).