Energy Spectrum of Two-Component Bose-Einstein Condensates in Optical Lattices

With the method of Green's function, we investigate the energyspectra of two-component ultracold bosonic atoms in opticallattices. We find that there are two energy bands for eachcomponent. The critical condition of the superfluid-Mott insulatorphase transition is determined by the energy band structure. Wealso find that the nearest neighboring and on-site interactions failto change the structure of energy bands, but shift the energybands only. According to the conditions of the phase transitions,three stable superfluid and Mott insulating phases can be found byadjusting the experiment parameters. We also discuss the possibilityof observing these new phases and their transitions in further experiments.