Excitation Spectra and Hard-core Thermodynamics of Bosonic Atoms In   Double Well Optical Lattices
  A general coupled representation is proposed for bosonic atoms in double well optical lattices. Based on such a representation, we investigate the excitation spectra and thermodynamics of bosonic atoms in the optical lattices. We find excitation spectra of the double well system with filling factor equal to one can be described by simultaneous excitations composed of pseudo particles corresponding to doubly occupied and empty double wells. It is demonstrated that hard-core bosonic statistics must be taken into account in order to properly describe the equilibrium properties at finite temperatures. For this we calculate the temperature dependence curves of particle numbers and heat capacity, in which the hard-core features are clearly shown. At last, the cases with filling factors unequal to one are also briefly discussed. 
Bao Xu, Hong-Ye Wu, Yi-Cai Zhang, Han-Ting Wang, Wu-Ming Liu
cond-mat.str-el