Condensation energy and the mechanism of superconductivity
  Condensation energy in a superconductor cannot be precisely defined if mean-field theory fails to hold. This implies that in the case of high temperature superconductors, discussions of quantitative measures of condensation energy must be scrutinized carefully, because the normal state is anomalous and the applicability of a mean-field description can be questioned. A related issue discussed here is the precise meaning of a superconducting transition driven by kinetic as opposed to one driven by potential energy; we argue that this is a semantic question. 
Sudip Chakravarty, Hae-Young Kee, Elihu Abrahams