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 slave-boson 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 finite-interaction case is investigated by numerical methods using 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 is compared with the observed specific-heat coefficient, gamma, of Sr1-xLaxTiO3 which is reported to significantly increase as x approaches unity.