Pseudospin S=1 formalism and skyrmion-like excitations in the three body   constrained extended Bose-Hubbard model
  We have focused in the paper on the most prominent and intensively studied S=1 pseudospin formalism for extended bosonic Hubbard model (EHBM) with truncation of the on-site Hilbert space to the three lowest occupation states n = 0, 1, 2. The EHBM Hamiltonian is a paradigmatic model for the highly topical field of ultracold gases in optical lattices. Generalized non-Heisenberg effective pseudospin Hamiltonian does provide a deep link with boson system and physically clear description of "the myriad of phases" from uniform Mott insulating phases and density waves to two types of superfluids and supersolids. We argue that the 2D pseudospin system is prone to a topological phase separation and focus on several types of unconventional skyrmion-like topological structures in 2D boson systems, which have not been analysed till now. The structures are characterized by a complicated interplay of insulating and the two superfluid phases with a single boson and two-boson condensation, respectively. 
A.S. Moskvin
cond-mat.supr-con cond-mat.str-el