Isotope Effect as a Probe of the Role of Phonons in Conventional and High Temperature Superconductors

We review the role of phonons in the mechanism of both conventional and high temperature superconductivity. We find that while on one hand most of the conventional superconductors fall within the framework of the BCS phonon-mediated pairing, on the other hand the complexity of the structural properties of High superconductors allows determination of only the partial (oxygen) isotope effect, with values ranging from negligibly small to even higher than BCS prediction. In either case, the study of isotope shift is important in its own right. We arrive at the conclusion that while phonons are central to explaining the mechanism of conventional superconductivity, their role should be taken into account for explaining High TC superconductivity, as well.