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 $\epsilon_{i}$ have a bimodal probability distribution and an energy separation $\Delta$. 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 $\Delta$ 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.