From BCS to Bose-Einstein condensation in a non-Fermi superconductor

We studied the possibility of a crossover from the BCS theory to a Bose-Ein stein condensation (BEC) for a non-Fermi system using the field theoretical method. We use as a description for the non-Fermi system the model propose d by Anderson, based on an anomalous Green function of the form G(k,omega) = g(alpha)omega (-alpha)(c)[i omega - epsilon (k)](1-alpha). We showed that this crossover is possible as a function of the interaction strength: the weak coupling limit can be described by the BCS theory and the strong coupl ing limit by the Bose-Einstein condensation of a preformed pairs gas. Using numerical methods we showed that the crossover is smooth, varying continuo usly as a function of the interaction constant. A more interesting result i s the fact that the same crossover can be discussed in terms of the non-Fer mi Anderson constant alpha.