The Metal-Insulator Transition in the Doubly Degenerate Hubbard Model

Abstract

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 withthe observed specific-heat coefficient, γ, of Sr_1-xLa_xTiO_3 which is reported to significantly increase as x approaches unity.