Singlet Even-Frequency and Triplet Odd-Frequency Superconductivity in the Two-Band Hubbard Model Based on the Dynamical Mean-Field Theory

Superconductivity in the two-band Hubbard model characterized by the on-site Coulomb repulsion U_d at d-site and the charge-transfer energy Δ between d- and p-sites is investigated on the basis of the dynamical mean-field theory. We calculate the pair susceptibilities for the s-wave symmetries with spin-singlet even-frequency and spin-triplet odd-frequency pairings and determine the superconducting transition temperature T_c at which the pair susceptibilities diverge. In the strong correlation regime where the system becomes Mott insulator at half-filling, the triplet superconductivity takes place in underdoped region while the singlet one takes place in overdoped region. In the both cases, T_c shows a maximum in the crossover region between Mott–Hubbard type (U_d < Δ) and charge-transfer type (U_d > Δ). We also observe a remarkable BEC-BCS crossover at a slightly doped region in the triplet superconductivity.