The Metal-Insulator Transition in the Doubly Degenerate Hubbard Model

A systematic study has been made on the metal-insulator (MI) transition of the doubly degenerate Hubbard model (DHM) in the paramagnetic ground state, by using the slaveboson mean-field theory which is equivalent to the Gutzwiller approximation (GA). For the case of infinite electron-electron interactions, we obtain the analytic solution, which becomes exact in the limit of infinite spatial dimension. On the contrary, the finiteinteraction case is investigated by numerical methods with the use of the simple-cubic model with the nearest-neighbor hopping. The mass-enhancement factor, Z, is shown to increase divergently as one approaches the integer fillings (N = 1, 2, 3), at which the MI transition takes place, N being the total number of electrons. The calculated N dependence of Z quantitatively accounts for the observed, specific-heat coefficient, γ, of Sr1−xLaxTiO3 which is reported to significantly increase as x approaches unity.