Fractional topological phase in one-dimensional flatbands with nontrivial topology

We show the existence of the fractional topological phase (FTP) in a one-dimensional interacting fermion model using exact diagonalization, in which the non-interacting part has flatbands with nontrivial topology. In the presence of the nearest-neighbouring interaction $V_{1}$, the FTP at filling factor $\nu =1/3$ appears. It is characterized by the three-fold degeneracy and the quantized total Berry phase of the ground-states. The FTP is destroyed by a next-nearest-neighbouring interaction $V_{2}$ and the phase diagrams in the $(V_{1},V_{2})$ plane is determined. We also present a physical picture of the phase and discuss its existence in the nearly flatband. Within the picture, we argue that the FTP at other filling factors can be generated by introducing proper interactions. The present study contributes to a systematic understanding of the FTPs and can be realized in cold-atom experiments.Comment: 5 pages, 5 figures. To appear in Phys. Rev.

Interaction effect in two-dimensional Dirac fermions

Based on the Dirac equations in the two-dimensional $\pi-$ flux model, we study the interaction effects both in nontrivial gapped and gapless Dirac equations with numerical exact diagonalization method. In the presence of the nearest and next nearest neighbor interactions: for nontrivial gapped Dirac equation, the topological phase is robust and persists in a finite region of the phase diagram; while for gapless Dirac equation, charge-density-wave and stripe phases are identified and the phase diagram in $(V_1, V_2)$ plane is obtained. When the next-next-nearest neighbor interaction is further included to gapless Dirac equation, the topological phase expected in the mean-field theory is absent. Our results are related to the possibility of dynamically generating topological phase from the electronic correlations.Comment: 7 pages, 8 figures. More discussins are added; accepted for publication in Physical Review

Interplay between single particle coherence and kinetic energy driven superconductivity in doped cuprates

Within the kinetic energy driven superconducting mechanism, the interplay between the single particle coherence and superconducting instability in doped cuprates is studied. The superconducting transition temperature increases with increasing doping in the underdoped regime, and reaches a maximum in the optimal doping, then decreases in the overdoped regime, however, the values of this superconducting transition temperature in the whole superconducting range are suppressed to low temperature due to the single particle coherence. Within this superconducting mechanism, we calculate the dynamical spin structure factor of cuprate superconductors, and reproduce all main features of inelastic neutron scattering experiments in the superconducting-state.Comment: 7 pages, 3 figures, typo correcte

Cold-atoms on a two-dimensional square optical lattice with an alternating potential

The cold-atom on a two-dimensional square optical lattice is studied within the hard-core boson Hubbard model with an alternating potential. In terms of the quantum Monte Carlo method, it is shown explicitly that a supersolid phase emerges due to the presence of the alternating potential. For the weak alternating potential, the supersolid state appears for the whole range of hard-core boson densities except the half-filling case, where the system is a Mott insulator. However, for the strong alternating potential, besides the supersolid and Mott insulating states, a charge density wave phase appears.Comment: 4 pages, 4 figure