The superconductor proximity effect in AuYBa2Cu3O7?? bilayer films: the role of order parameter anisotropy
Scanning tunneling spectroscopy of AuYBa2Cu3O7?? bilayers reveals proximity effect features that reflect the anisotropic dx2?y2 d x 2 ? y 2 -wave order parameter in YBa2Cu3O7?? (YBCO). No proximity effect takes place at the (001)YBCOAu interface, manifesting the quasi two-dimensional nature of the order parameter. Proximity gaps are induced in the gold primarily via (100)YBCO facets, and their size decays exponentially on a scale of ?30nm, in good agreement with estimations for the dirty limit. In the nodal (110)YBCOAu interface, the proximity effect manifests itself by the penetration of Andreev bound states into the gold. The corresponding zero bias conductance peaks are nearly constant in magnitude for Au layers thinner than 7nm, and then decay abruptly with Au thickness, vanishing above 10nm, on the scale of the (ballistic) mean free path.
proximity effect tunneling spectroscopy high temperature superconductors scanning tunneling microscopy