Quasiequilibrium Mixture of Itinerant and Localized Bose Atoms in Optical Lattice

Conditions are studied under which there can exist a quasiequilibrium mixture of itinerant and localized bosonic atoms in an optical lattice, even at zero temperature and at integer filling factor, when such a coexistence is impossible for an equilibrium lattice. The consideration is based on a model having the structure of a two-band, or two-component, boson Hubbard Hamiltonian. The minimal value for the ratio of on-site repulsion to tunneling parameter, necessary for the occurrence of such a mixture, is found.