A phenomenological description of the high-T-c superconductors based on the
Cooperon propagator is presented. This model allows one to study the effec
ts of local pairing correlations and long-range phase fluctuations on the s
ame footing, both above and below T-c. Based on numerical calculations, it
is shown that the two types of correlations contribute to the gap/pseudogap
in the single-particle excitation spectra. The concourse of these two effe
cts can induce low energy states, which should be observable in underdoped
materials at very low temperature. (C) 2001 Elsevier Science B.V. All right
s reserved.