Inverse Isotope Effect in PdH(D)

In this letter, we take a new approach to the explanation of the inverse isotope effect in PdH(D). Our approach introduces two new aspects. First, we took into account the experimental evidence that at temperatures below 50 K, the crystal structure of PdH and of PdD is zincblende. Second, we studied the contribution of both, the electron-phonon and the electron-electron interactions. We used the Migdal-Eliashberg theory to perform our ab initio calculations. We found that the electron-electron contribution is the most important one to explain the inverse isotope effect. We reproduced the experimentally found values for the critical temperature and the isotope coefficient. Our analysis represents a direct and simple explanation for the inverse isotope effect in PdH(D).