SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY OF THIN-FILM SUPERCONDUCTOR PB

A variable-temperature scanning tunneling microscope system, which operates in the temperature range of 4 < T < 400 K, was employed to perform topographic and spectroscopic studies of conventional superconductors at low temperatures. Images of Pb thin films were obtained and local tunneling spectroscopy was performed. The N-I-S tunneling characteristic revealing superconducting gap structure was observed. In mapping the electronic density of states over the Pb surface, abrupt changes in the measured N-I-S tunneling characteristics were found, showing the existence of apparent normal surface regions. The implications of the tunneling spectroscopy results are discussed.