Anisotropic superconducting gap of Bi₂Sr₂CaCu₂O₈ : tunneling spectroscopy with STM

Abstract
The tunneling conductance was measured in the superconducting phase of Bi₂Sr₂CaCu₂O₈ with use of the STM and the temperature dependence of magnetic field penetration depth was also investigated by the magnetization measurement. The obtained differential conductance is reduced to almost zero and flat near zero bias voltage indicating the finite gap on the whole Fermi surface, while a considerable gap anisotropy is found. The total conductance curve was explained by the anisotropic gap ranging from 10 meV to 30 meV. The temperature dependence of penetration depth is of the thermal activation type with the activation energy of 14 meV. These results indicate that the superconductivity in cuprate high T_C superconductor is given by the attractive interaction between electrons of the predominant s-wave symmetry mixed with the d-wave.