ANHARMONIC PHONON STRUCTURE IN THE TUNNELING CONDUCTANCE OF BI-CUPRATES

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