REVERSE ISOTOPE EFFECT ON THE SUPERCONDUCTIVITY OF PDH, PDD, AND PDT

The reverse isotope effect on the superconducting transition temperatu re of PdH, PdD, and PdT is quantitatively explained by incorporating t he effects of the zero-point motion of Pd and H on the electronic stru cture of the system. The vibration of the Pd atom smears out its charg e distribution in space. The corresponding potential is felt by the vi brating H, D, and T atoms. This interaction modelled in terms of the D ebye-Waller mechanism is shown to have a significant effect on the ele ctron-phonon coupling constant. The anharmonicities in the phonon spec tra and the electronic structure influenced by the vibrating atoms pla y a major role in the observed isotope dependence of the transition te mperature.