2 M ay 1 99 4 Comment on “ Evolution from BCS Superconductivity to Bose - Einstein Condensation : Role of the Parameter k F ξ in Interpreting the Experimental Plot

The problem of crossover from BCS to Bose-Einstein condensation has recently attracted considerable interest owing to the discovery of high-Tc cuprates. Their short coherence length, ξ, places these materials in the interesting region between BCS and Bose-Einstein condensation. In the paper of F. Pistolesi and G.C. Strinati (Phys. Rev. B 49, 6356 (1994)), the Nozières and Schmitt-Rink approach (NSR) is taken, which is valid for the weak coupling regime. They derive a relation between Tc and TF, which they insist is valid for any coupling strength. We present arguments that their assumptions are incorrect by using our fully self-consistent T-matrix formalism in two dimensions, and show that the NSR approach produces unphysical results in ∗Permanent Address: Departamento de F́ısica, Grupo de Sólidos, FEC LUZ, Apartado 526, Maracaibo, Venezuela. Also a Visiting Scientist at IVIC, Centro de F́ısica, Apartado 21827, Caracas 1020-A, Venezuela, Corresponding author: J.J. Rodŕıguez-Núñez, E-mail: [email protected]