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 {ital 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 {vert bar}{ital k}{minus}{ital k}{sub {ital F}}{vert bar} increases. For {Delta}{sub 0}{approximately}10{sup {minus}2} of the bandwidth, which estimates suggest is the appropriate range of values for the high-temperature superconductors, one finds that {Delta}{sub 0} is reduced by {approximately}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.