Abstract
Applying the generalized Bose-Einstein condensation (GBEC) formalism, we extend the BCS-Bose crossover theory by explicitly including hole Cooper pairs (2hCPs). From this, follows a phase diagram with two pure phases, one with 2hCPs and the other with electron Cooper pairs (2eCPs), plus a mixed phase with arbitrary proportions of 2eCPs and 2hCPs. The special-case phase when there is perfect symmetry, i.e., with ideal 50-50 proportions between 2eCPs and 2hCPs, corresponds to the usual BCS-Bose crossover. Explicitly including 2hCPs yields an extended BCS-Bose crossover which predicts improved T c /T F values for some conventional superconductors (i.e., with electron-phonon dynamics) when compared with experiment. To do this, we employ the BCS dimensionless coupling constant λ B C S via the BCS gap equation and compare with the Bogoliubov et al. upper limit λ B C S ≤ 1/2. Another phase diagram presented exhibits experimental T c /T F values for some conventional superconductors for arbitrary proportions between 2eCPs and 2hCPs as function of Δn = n/n f − 1, where n is the electron concentration and n f that of unbound electrons at T = 0. The extended crossover is compared with experimental T c /T F values as well as to the gap-to- T c ratio.
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Chávez, I., García, L.A., Grether, M. et al. Extended BCS-Bose Crossover. J Supercond Nov Magn 31, 631–637 (2018). https://doi.org/10.1007/s10948-017-4383-z
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DOI: https://doi.org/10.1007/s10948-017-4383-z