Volume dependence of superconducting state parameters of bismuth-based binary alloys: A pseudopotential approach

Abstract

A comprehensive and systematic study of superconducting state parameters (SSPs) of Bi-based binary alloys of the form [Formula: see text] has been carried out in the framework of pseudopotential theory at different concentrations ([Formula: see text]) of impurity atom-[Formula: see text] in host atom Bi which varies from 0 to 1. Impurity atom [Formula: see text] has been replaced by In, Tl, Sb and Pb to form four alloy systems. The density-based local form of the pseudopotential proposed by Fiolhais et al. has been used in this study to compute SSPs such as electron–phonon coupling strength ([Formula: see text]), Coulomb pseudopotential ([Formula: see text]), transition temperature ([Formula: see text]), effective interaction strength ([Formula: see text] and isotopic effect parameter ([Formula: see text]) of Bi-based binary alloy systems. Computed results of SSPs of alloys under study are in good agreement with available experimental and other theoretical results. In order to investigate the effect of pressure on SSPs of alloys under study, a theoretical calculation of SSPs as a function of compressed volume is reported. The volume dependence of Debye temperature has been accounted by using Debye–Gruneisen model which involves the Gruneisen parameter. Thus, to describe the effect of pressure on SSPs accurately, the value of Gruneisen parameter should be as accurate as possible. But reported results of Gruneisen parameter in the literature are highly scattered. Due to this reason, we have used two sets of Gruneisen parameter obtained by different methods to understand its role in the computation of SSPs as a function of compressed volume. Further, critical volumes for all alloys at different concentration have been predicted at which electron–phonon coupling strength and Coulomb pseudopotential are equal ([Formula: see text]). At critical volume, superconductivity quenches where transition temperature, [Formula: see text], and effective interaction strength, [Formula: see text], become zero. It is observed that critical volumes predicted by all approaches used in this study are in excellent agreement with each other.