Tunneling Conductance of a Bi2Sr2CaCu2O8-GaAs Junction along the c-Axis

Anisotropy in the energy gap of Bi2212 was investigated by using a point contact tunneling junction and it was noted that there was very little anisotropy. When a GaAs needle was contacted perpendicular to the c -plane, at least two kinds of conductance curves were obtained, one with a gap of 42 meV and the other with a gap of 64 meV. In the latter, phonon structures extended to a higher voltage and a three-phonon process was observed similar to our multiphonon exchange model for superconductivity.