Experimental Evidence for an Atomic-like Parameter Characterizing the Systematics of Superconductivity in the Transition Metals

Abstract

In a recently published paper1 we have presented experimental data on the superconducting critical temperature T c of amorphous transition metals (elements and alloys of neighboring elements) for the 4d and 5d series. We suggested that the data are consistent with the presence of a parameter first introduced by Hopfield,2 which characterizes the systematics of superconductivity in the transition metal (TM) series.‡ An unexpected result, however, is that the data indicate that this parameter η has a sharp triangular peak in the center of the d series at five d electrons per atom. This occurs for the 4d TM series at an electron-to-atom ratio e/a of 6.4. This behavior is contrary to the predictions of Bennemann and Garland,3 in which η has a smooth maximum on the right side of the TM series. In this paper we discuss other evidence, using data in the literature for the crystalline TM, indicating that η has a peak in the center of the 4d series.