Barrier parameters and superconducting gap structure of the etched surface of Y−Ba−Cu−O by scanning tunnelling spectroscopy

Summary Using a scanning tunnelling microscope, the tunnelling currentvs. voltage is measured between a gold tip and the chemically etched (001) surface of YBa₂Cu₃O _x crystals at room temperature. The tunnelling barrier height and thickness are derived by modelling the system in the normal state as a conventional N-I-N junction. TheI(V) andG(V) curves are computed for the same junction in the superconducting state (N-I-S junction). The predicted gap structure for a single BCS-Dynes-like gap is simple and has low zero-bias conductance. The complexG(V) spectra measured belowT _c on the etched junctions with ∼ 50% zero-bias conductance suggest a possible multilayer contribution in the unit cell. In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.