Quantum phases of 7Li atoms in an optical lattice

We study the quantum phases that may arise when Li-7 atoms that possess an attractive two-body interaction are loaded into an optical lattice. The phase diagram that we have obtained for Li-7 atoms within a mean-field approximation is composed of the superfluid and Mott-insulator phases as for bosonic atoms with a repulsive two-body interaction. We have found that the repulsive three-body interaction plays a vital role in stabilizing the quantum phases of Li-7 atoms in an optical lattice. The ground-state energy and the average atom number per lattice site in the quantum phases have been calculated and found to be consistent with the nature of these quantum phases. The excitation spectra of quasi-particles and quasi-holes in the Mott-insulator phase have also been calculated. In our general investigation of the effects of the three-body interaction that is allowed to vary, we have found that the energies of quasi-particles are substantially increased as the strength of the repulsive three-body interaction is raised, whereas the energies of quasi-holes are slightly decreased at low-filling factors of atoms and substantially decreased at large filling factors.