ISOTOPE EFFECT AND T-C SUPPRESSION IN D-WAVE SUPERCONDUCTORS

We have studied the isotope effect on the superconducting transition t emperature T-c of d-wave pairing instabilities due to antiferromagneti c spin fluctuation exchange. We found that models with conventional co upling to harmonic phonon degrees of freedom and reasonable limits on coupling strength and phonon spectra, give values for the isotope expo nent alpha which are at least one order of magnitude smaller than typi cal observed values of alpha in the cuprates. Models with coupling to non-linear tunneling modes in a strongly anharmonic multi-well lattice potential and realistic coupling strengths have effectively larger is otopic mass dependences and may therefore account for the observed mag nitudes of alpha.