Magnetism and Superconductivity in a Two-band Hubbard Model in Infinite Dimensions

We study a two-band Hubbard model using the dynamical mean-field theory combined with the exact diagonalization method. At the electron density n =2, a transition from a band-insulator to a correlated semimetal occurs when the on-site Coulomb interaction U is varied for a fixed value of the charge-transfer energy Δ. At low temperature, the correlated semimetal shows ferromagnetism or superconductivity. With increasing doping | n -2|, the ferromagnetic transition temperature rapidly decreases and finally becomes zero at a critical value of n . The second-order phase transition occurs at high temperature, while a phase separation of ferromagnetic and paramagnetic states takes place at low temperature. The superconducting transition temperature gradually decreases and finally becomes zero near n =1 ( n =3) where the system is Mott insulator which shows antiferromagnetism at low temperature.