Does the isotope effect of mercury support the BCS theory?

Abstract

In this paper, we reexamine the results of isotope effect experiments of the conventional monoatomic superconductor (Hg). It is shown clearly that the isotopic coefficients of mercury can be largely deviated from $\alpha=0.5$, the standard value suggested by the phonon-mediated BCS pairing theory. According to the reported experimental results of various mercury isotopes, a giant isotope effect ($\alpha=2.896$) is numerically found in the data. This study indicates that the validity of the conventional BCS theory cannot be verified by the isotope effect.