Tunneling observation of phonon contribution to the pairing interaction in oxide superconductors

Tunneling conductance spectra were observed by point contact junction of SIN on single crystals of BSCCO (2212). Outside of the definite gap structure edge, significant fine structures were observed almost reproducibly ranging to 0.2 eV. The conductance derivative peaks both in positive and negative bias range were found in well one by one correspondence with the phonon spectrum peaks reported by Renker et al. [1]. Most of the peak modes were attributed to the optical phonons due to the oxygen oscillations in and around the [CuO2](n) net-plane. Numerical computation in terms of the Eliashberg gap equation was carried out, and the electron-phonon coupling intensity function alpha(2)F(omega) was elucidated and it turns out that the breathing mode relating to the polaronic valence fluctuations are predominant as compared with the B-1g mode regarding the spin correlations.