Abstract
We have performed a detailed study of the tunneling spectra of bicrystal grain-boundary junctions (GBJ’s) fabricated from the high-temperature superconductors (HTS) (YBCO), (BSCCO), (LSCO), and (NCCO). In all experiments the tunneling direction was along the planes. With the exception of NCCO, for all materials a pronounced zero bias conductance peak (ZBCP) was observed that decreases with increasing temperature and disappears at the critical temperature. These results can be explained by the presence of a dominating d-wave symmetry of the order parameter resulting in the formation of zero-energy Andreev bound states at surfaces and interfaces of HTS. The absence of a ZBCP for NCCO is consistent with a dominating s-wave symmetry of the pair potential in this material. The observed nonlinear shift of spectral weight to finite energies by applying a magnetic field is in qualitative agreement with recent theoretical predictions.
- Received 10 February 1998
DOI:https://doi.org/10.1103/PhysRevB.58.11197
©1998 American Physical Society