D-WAVE SUPERCONDUCTIVITY IN NARROW-BAND SYSTEMS - THE EFFECT OF 2ND-NEAREST-NEIGHBOR HOPPING, THE ISOTOPE EFFECT, AND THE PRESSURE EFFECT

The effect of second-nearest-neighbour hopping on the transition tempe rature and the superconducting order parameter are investigated for d- wave superconductivity within the framework of the extended Hubbard mo del for both weak- and strong-correlation cases. The variation of the gap ratio with carrier concentration is studied. The isotope-shift exp onent and the pressure coefficient of the transition temperature are i nvestigated, taking into consideration isotopic mass and pressure depe ndences of the hopping and effective attractive interaction terms. The predicted variation of the isotope-shift exponent and the pressure co efficient with doping are in qualitative agreement with experimental f indings for the high-T-c oxides.