Absence of an Isotope Effect in Superconducting Ruthenium

Abstract

The superconducting isotope effect is examined in five Ru specimens by measurements of the bulk magnetization, which show the effect of isotopic composition on the superconducting critical field. All specimens showed excellent superconducting behavior, and a typical series of isothermal transitions is plotted. To avoid uncertainty associated with absolute temperature measurements, the isothermal critical field differences of four of the specimens was measured relative to one specimen used as a reference. The data confirm that the superconducting isotope effect does not occur in Ru and indicate that, if Ru has any isotope effect at all, it must be at least an order of magnitude smaller than that shown by the nontransition superconducting elements. (H.D.R.)