Cooper Pairs Distribution function for bcc Niobium under pressure from first-principles

Abstract

In this paper, we report Cooper Pairs Distribution function Dcp(ω, Tc) for bcc Niobium under pressure. This function reveals information about the superconductor state through the determination of the spectral regions for Cooper-pairs formation. Dcp(ω, Tc) is built from the well-established Eliashberg spectral function and phonon density of states, calculated by first-principles. Dcp(ω, Tc) for Nb suggests that the low-frequency vibration region (ω<6meV) is where Cooper-pairs are possible. From Dcp(ω, Tc) , it is possible to obtain the Ncp parameter, which is proportional to the total number of Cooper-Pairs formed at a temperature Tc. The Ncp parameter allows an approach to the understanding of the Nb Tc anomalies, measured around 5 and 50 GPa.