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

Abstract

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