Mott-Hubbard metal-insulator transition at non-integer filling

Correlated electrons in a binary alloy $A_x{B}_{1-x}$ are investigated within the Hubbard model and dynamical mean–field theory (DMFT). The random energies ${ϵ}_i$ have a bimodal probability distribution and an energy separation $\mathrm{\Delta }$. We solve the DMFT equations by the numerical renormalization group method at zero temperature, and calculate the spectral density as a function of disorder strength $\mathrm{\Delta }$ and interaction $U$ at different fillings. For filling factors $\nu =x$ or $1+x$ the lower or upper alloy subband is half filled and the system becomes a Mott insulator at strong interactions, with a correlation gap at the Fermi level. At the metal–insulator transition hysteresis is observed. We also analyze the effective theory in the $\Delta \to \infty $ limit and find good agreement between analytical and numerical results for the critical interaction $U_c$ at which the metal–insulator transition occurs.