Two-particle self-consistent approach to unconventional superconductivity

A nonperturbative approach to unconventional superconductivity is developed based on the idea of two-particle self-consistent (TPSC) theory by Vilk and Tremblay. A sum rule, which the momentum-dependent pairing susceptibility satisfies, is derived. An effective pairing interaction between quasiparticles is determined so that the susceptibility should fulfill this exact sum rule, in which fluctuations belonging to different symmetries couple at finite momentum. It is demonstrated that the mode coupling between d-wave and s-wave pairing fluctuations leads to suppression of the d-wave fluctuation near the Mott insulator.