Abstract
In this paper, we report Cooper Pairs Distribution function {D}_{cp}(omega ,{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}) is built from the well-established Eliashberg spectral function and phonon density of states, calculated by first-principles. {D}_{cp}(omega ,{T}_{c}) for Nb suggests that the low-frequency vibration region left(omega <6 ,{text{meV}}right) is where Cooper-pairs are possible. From {D}_{cp}(omega ,{T}_{c}), it is possible to obtain the {N}_{cp} parameter, which is proportional to the total number of Cooper-Pairs formed at a temperature {T}_{c}. The {N}_{cp} parameter allows an approach to the understanding of the Nb {T}_{c} anomalies, measured around 5 and 50 GPa.
Highlights
In this paper, we report Cooper Pairs Distribution function Dcp(ω, Tc) for bcc Niobium under pressure
Details of the Fermi surface are different: the low-pressure anomaly is invisible in the band structure and it is associated with a global decrease of the nesting factor in the whole Brillouin Zone, while the high-pressure anomaly relates to a well-pronounced change in the band structure
We report the Cooper Pairs Distribution functions Dcp(ω, Tc) for Nb under pressure, which are built from the well-established Eliashberg spectral function α2F(ω) and phonon density of states (PhDOS), calculated by first-principles
Summary
We report Cooper Pairs Distribution function Dcp(ω, Tc) for bcc Niobium under pressure. 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. Niobium (Nb) is a conventional superconductor with a body-centered cubic (bcc) structure. Niobium (Nb) is a conventional superconductor with a body-centered cubic (bcc) structure It has a lattice constant of 6.24 Bohr[1] and a superconducting critical temperature (Tc) of 9.25 K2, Nb is the element with the highest Tc. Critical temperature measurements under pressure Tc(P) by Struzhkin et al.[3] show discontinuities of Tc around 4−5 GPa and 50−60 GPa , where Tc increases by 0.7 K and decreases by about 1 K, respectively. A complete description of this behavior could lead us to new physics and a deeper understanding of the superconducting phenomenon
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