SCANNING TUNNELING SPECTROSCOPY ON HIGH-TC SUPERCONDUCTORS

Superconducting pp structures of Bi2Sr2CaCuOy (BSCCO) and YBa2Cu3Oy (Y BCO) have been probed by the scanning tunneling microscopy (STM) at cr yogenic temperatures. The tunneling conductance curves observed on bul k single crystals of BSCCO and epitaxial thin films of YBCO revealed c lear overshooting peaks and flat bottom regions around V=0 with quite low zero bias conductances of approximately 1 %. Since the electron tu nneling process in STM is essentially incoherent, the present observat ions is favored by the s-wave pairing mechanism. However, the conducta nce curves were found to be substantially smeared in comparison with t he conventional excitation spectra predicted in the BCS (isotropic s-w ave) superconductors, suggesting the anisotropy of the gap functions.