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1. Quantum phases in extended Bose-Hubbard models
Quantum phase transition between the superfluid state and the Mott-insulator state is studied based on an extended Bose-Hubbard model with two- and three-body on-site interactions. By employing the mean-field approximation we find the extension of the insulating “lobes” and the existence of a fixed point in three-dimensional phase space. We investigate the link between experimental parameters and theoretical variables. The possibility to observe our results through some experimental effects in optically trapped Bose-Einstein condensates is also discussed.
Bolun Chen, X.-B. Huang, S.-P. Kou, Y Zhang, Physical Review A 78 (4), 043603
We further analyze the quantum phases of multicomponent Bose-Hubbard models in optical superlattices based on a mean-field method, that is, the decoupling approximation. The global phase diagrams exhibit complex patterns with various charge-density-wave orders for both one- and two-component cases. We further calculate the effective spin excitations for the two-component case in the strong-coupling region at unit filling, and show the existence of a spin-density-wave order. The results of our study can be tested straightforwardly with current cold-atom experimental techniques.
Bolun Chen, S.-P. Kou, Y Zhang, S Chen, Physical Review A 81 (5), 053608
2. Exotic excitations in correlated bosonic systems
We systematically analyze the properties of the bosonic t–J model simulated in optical superlattices. In particular, by using a slave-particle approach, we show the emergence of a strange topological Fermi liquid with Fermi surfaces from a purely bosonic system. We also discuss the possibility of observing these phenomena in ultracold atom experiments. The result may provide some crucial insights into the origin of high-Tc superconductivity.
Bolun Chen, S.-P. Kou, Modern Physics Letters B 25 (11), 813-821
3. Symmetry-based classifications of topological insulators
In this paper, we find that topological insulators with time-reversal symmetry and inversion symmetry featuring two-dimensional quantum spin Hall (QSH) state can be divided into 16 classes, which are characterized by four Z_2 topological variables ζ_k = 0, 1 at four points with high symmetry in the Brillouin zone. We obtain the corresponding edge states for each one of these sixteen classes of QSHs. In addition, it is predicted that massless fermionic excitations appear at the quantum phase transition between different QSH states. In the end, we also briefly discuss the three-dimensional case.
L.-F. Liu, Bolun Chen, S.-P. Kou, Communications in Theoretical Physics 55 (5), 904
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