Mott Transitions in the Multiband Hubbard Model through Variational Wave Functions

We study the multi-band Hubbard model with two or three degenerate bands by using correlated variational wave functions and Monte Carlo methods. Here, the interplay among electronic Coulomb repulsion, kinetic energy and the Hund's coupling gives rise to a rich phase diagram. Imposing a paramagnetic wave function, we have obtained the Mott metal-insulator transitions when the electronic filling is commensurate (i.e., for n=1, 2, and 3) at finite values of the Coulomb repulsions U_c(n). In agreement with previous Dynamical Mean-Field theory results, we observe that the inclusion of the Hund's coupling J lowers the value of U_c(n) at half filling, while it leads to an increase of U_c(n) for other fillings. At half-filling, the transition is first order for both J equal and different from 0. At non-commensurate filling and finite J, we report the existence of a large region of spin-triplet superconductivity with inter-band pairing. By contrast, a (singlet) d-wave intra-band pairing is present only when the intra-band Coulomb repulsion is larger than the inter-band one.