The two-orbital Hubbard model and the OSMT

We analyze the two-orbital Hubbard model by means of the Composite Operator Method with the aim at studying the phenomenon of orbital selective Mott transition (OSMT). The model contains an interorbital interaction $U'$, in addition to the usual intraorbital one $U$. As warming-up approximation, we use a basis of two operators only, the Hubbard operators. The analysis of the density of states at the chemical potential as a function of the ratio between the bandwidths of the two orbitals shows the clear signature of an orbital selective Mott transition as expected.