A look at the crossover region between BCS superconductivity and Bose Einstein Condensation

Pair fluctuation theory has been used to study the crossover from the weak coupling BCS theory to the strong coupling Bose Einstein Condensation. The effect of fluctuations has been studied over the whole crossover regime. It has been shown that the pair fluctuations are enhanced considerably in both two and three dimensions and hence mean field theory is inadequate to study the physical properties in this regime. A self consistent scheme for calculating the pair susceptibility is given.