Critical fluctuations in the attractive Hubbard model

One possible scenario for the critical properties of high-temperature superconductors in the underdoped regime takes into account the critical slowing down of two fluctuation fields associated to density and to Cooper pairs. The first is due to the instability toward a CDW ordering and the second to the instability to superconductivity. We develop a nonperturbative theory of this regime in the framework of the attractive Hubbard model. Above a critical temperature, the particles move under the action of a static field whose direction fixes the relative weight of density and Cooper pair fluctuations. (C) 2000 Elsevier Science B.V. All rights reserved.