STM study of anisotropic superconducting gap of Bi-based oxides

Abstract

The electron tunneling study was done on both Bi 2Sr 2CaCu 2O 8 and Bi 2Sr 2CaCu 2−xNi xO 8 with use of STM and temperature dependence of the magnetic field penetration depth was also investigated. The tunneling conductance obtained at the lateral surface of single crystal of Bi 2Sr 2CaCu 2O 8 indicates the finite gap on the whole Fermi surface, while the considerable anisotropy is found. The temperature dependence of the penetration depth is of the thermal activation type. These results indicate symmetry of the pair wave function is the predominant s-wave mixed with the d-wave. For Bi 2Sr 2CaCu 2−xNi xO 8, any clear gap structure was not found in the tunneling conductance at the cleaved surface. The penetration depth exhibits the T 2 temperature dependence.