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DOE OSTI · 22777023

Extended BCS-Bose Crossover

García, L. A.·Grether, M.·Llano, M. de·Tolmachev, V. V.
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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{sub c}/T{sub 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{sub BCS} via the BCS gap equation and compare with the Bogoliubov et al. upper limit λ{sub BCS} ≤ 1/2. Another phase diagram presented exhibits experimental T{sub c}/T{sub F} values for some conventional superconductors for arbitrary proportions between 2eCPs and 2hCPs as function of Δn = n/n{sub f} − 1, where n is the electron concentration and n{sub f} that of unbound electrons at T = 0. The extended crossover is compared with experimental T{sub c}/T{sub F} values as well as to the gap-to- T{sub c} ratio.

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74 ATOMIC AND MOLECULAR PHYSICS75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITYBOSE-EINSTEIN CONDENSATIONCOMPARATIVE EVALUATIONSCONCENTRATION RATIOCOOPER PAIRSCOUPLING CONSTANTSELECTRONSHOLESPHASE DIAGRAMSPHONONSSTRONG-COUPLING MODELSUPERCONDUCTORSSYMMETRY

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García, L. A., Grether, M., Llano, M. de, Tolmachev, V. V.. 2018-03-15. Extended BCS-Bose Crossover. https://doi.org/10.1007/s10948-017-4383-z

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