Mott transition in degenerate Hubbard models: Application to doped fullerenes

The Mott-Hubbard transition is studied for a Hubbard model with orbital degeneracy $N$, using a diffusion Monte Carlo method. Based on general arguments, we conjecture that the Mott-Hubbard transition takes place for $\frac{U}{W}\sim \sqrt{N}$, where $U$ is the Coulomb interaction and $W$ is the bandwidth. This is supported by exact-diagonalization and Monte Carlo calculations. Realistic parameters for the doped fullerenes lead to the conclusions that stoichiometric $A_3{\mathrm{C}}_{60}(A=\mathrm{K},\mathrm{R}\mathrm{b})$ are near the Mott-Hubbard transition, in a correlated metallic state.