ISOTOPE EFFECT IN D-WAVE SUPERCONDUCTORS

Based on recently proposed antiferromagnetic spin fluctuation exchange models for d(x2-y2) superconductors, we show that coupling to harmoni c phonons cannot account for the observed isotope effect in the cuprat e high-T-c materials, whereas coupling to strong anharmonic multiple-w ell lattice tunneling modes can. Our results thus point towards a stro ngly enhanced effective electron-phonon coupling and a possible breakd own of Migdal-Eliashberg theory in the cuprates.