SUPERCONDUCTING GAP RATIO AND ISOTOPE-SHIFT EXPONENT IN A PAIR-TUNNELING MODEL

The superconducting transition temperature (T-c), superconducting gap ratio and isotope-shift exponent (alpha) are studied in a narrow band system with a two-dimensional band structure assuming an intra-plane p airing kernel, due to electron-phonon interactions and an interlayer t unneling of Cooper pairs for both isotropic s-wave and d-wave pairing. The pair-tunneling process enhances T-c and the gap ratio while lower s alpha for both cases. The effect of an extended van Hove singularity in the electronic density of states on the gap ratio and alpha is inv estigated. The results an compared with the experimental findings of h igh-T-c cuprates. (C) 1998 Elsevier Science B.V.