Doping dependence of the superconducting gap in YBa2Cu3O7-delta

Using the quasiparticle spectra in the superconducting state, as determined by the eight-band model for YBa2Cu3O7 and a phenomenological interaction c onstant K we have studied the doping dependence of the maximum superconduct ing gap. Surprisingly, our results agree qualitatively with the lower of th e two energy scales identified in a recent report by Deutscher [Nature 397 (1999) 410]. Thus, we conclude that this coherence energy range Delta (c), measured by Andreev reflection, penetration depth, and Raman experiments, i s a BCS-like, weak coupling, d-wave energy gap. Unfortunately, with regard to the other energy scale Delta (p) our theory has nothing to contribute. N evertheless, we suggest that it is not a superconducting feature of the spe ctra. (C) 2001 Elsevier Science B.V. All rights reserved.