Scanning tunneling spectroscopy on low- and high-T-c superconductors

Using some sophisticated modes of scanning tunneling spectroscopy the local density of states on two superconducting compounds in the superconductive state at 4.2 K were analyzed, On NbSe2 which is a type-II low-T-c material, the Abrikosov flux line lattice was imaged for various external magnetic fields up to B-C2. The field-induced decrease of the vortex core radius for increasing magnetic field, which was recently predicted by a microscopic theory, could be clearly verified. On sputtered YBa2Cu3O7-delta films the measurements yielded some distinct types of the surface density of states involving gaps, being in accordance to the Bardeen-Cooper-Schrieffer theory, unexpectedly large gaps, Coulomb staircases, and zero-bias peaks. (C) 1996 American Vacuum Society.