CRYOGENIC STM STS OBSERVATION ON OXIDE SUPERCONDUCTORS

The topographic and electronic properties of the surfaces of (001) and (110) oriented YBa2Cu3Oy epitaxial films have been probed by atomic r esolution STM/STS at 4.2 K. The STM image on the (001) surface clearly revealed the atomic corrugation of the tetragonal lattice with an ave rage spacing of 0.4 nm, while on the (110) surface the orthorhombic at omic lattice, corresponding to the Cu atoms of both CuO2 and CuO chain planes, was observed. The STS result on the (001) surface indicated t he semiconducting nature of the terminating layer. As the tunneling ti p came closer to the surface, however, the shape of the tunneling spec trum became more metallic and showed a superconducting energy gap, whi ch seems to arise from the underlying superconducting layer. On the ot her hand, the tunneling spectra on the (110) surface indicated superco nducting gap structures, independent of the tip-sample distance.