Anharmonic Phonon Structure in the Tunneling Conductance of Bi-Cuprates

Phonon structures in the tunneling conductance must be properly normalized to evaluate the intensity of the electron-phonon interaction. However, this is very difficult because of the absence of the exact normal-state conductivity. Therefore we propose another method to judge whether or not the intensity becomes stronger with a critical temperature T c. This method compares the intensity of anharmonic structures, which are normalized to the single-phonon structures, between high- and low-T c substances. Our data for Bi-cuprates strongly suggest that the electron-phonon interaction is stronger in higher-T c substances.