A systematic study of pairing fluctuations in two dimensions about a BCS-like mean-field theory is performed. It is based upon the large-N limit of models with symplectic [Sp(N)] symmetry. The leading corrections to the critical temperature and the chemical potential in two dimensions are found to be of order (lnN)/N and do not significantly alter the physical scenario of the mean-field theory. The results are applicable to models with short-range attractive interactions between opposite-spin electrons, e.g., the negative U Hubbard model or the t-J model.

• Received 3 December 1990

DOI:https://doi.org/10.1103/PhysRevB.43.10229