FLEX+DMFT approach for superconductivity in multi-band systems: A study on bilayer Hubbard model

Broadly speaking, to enhance the superconducting transition temperature T_c, a strong paring interaction and a light electron effective mass are favorable. However, the strong pairing interaction not only enhance superconductivity, but also results in the strong quasi-particle renormalization in general. As a way to circumvent this dilemma, we can consider the multi-band Hubbard model as discussed in the previous studies [1, 2]. In multi-band systems, spin fluctuations with finite energy arising from interband scattering channels can develop and act as an effective pairing interaction. Finite energy fluctuations do not cause an abovementioned strong competition between the quasi-particle renormalization and superconductivity. To treat both local and non-local correlations, we have applied the FLEX (fluctuation exchange) + DMFT (dynamical mean-field theory) method [4, 5] to the bilayer Hubbard model. In the presentation, we will discuss the correlation effects and the superconductivity arising from the interband pair scattering.
[1] K. Kuroki, et al., Phys. Rev. B 66, 184508 (2002). [2] T. Maier and D. J. Scalapino, Phys. Rev. B 84, 180513 (2011). [3] J. Gukelberger, et al., Phys. Rev. B 91, 235114 (2015). [4] M. Kitatani, et al., Phys. Rev. B 92, 085104 (2015).