Effect of the operator nature of the superconducting order parameter in the presence of an added quasiparticle

Abstract

I investigate corrections to the mean-field approximation for a superconductor at zero temperature using a single-band Hubbard model with an on-site attractive interaction U. These corrections arise from treating the order parameter as an operator rather than as a number. The quasiparticle spectra may be characterized by a renormalized gap and an effective mass that fall rapidly as ‖k-kF‖ increases. For Δ0∼10−2 of the bandwidth, which estimates suggest is the appropriate range of values for the high-temperature superconductors, one finds that Δ0 is reduced by ∼20% both for a parabolic band and for the tight-binding band structure at half-filling. This is comparable to the magnitude of renormalization found for pairing bags.

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