Topological phase transitions on the square-octagon lattice with next-nearest-neighbor hopping

Abstract

We investigate the topological phase transitions on the square-octagon lattice with an intrinsic spin-orbit coupling and an additional real next-nearest-neighbor hopping. We study the evolution of the band structure under the next-nearest-neighbor hopping parameters. Based on the spin Chern numbers, we present the phase diagrams of our model and find that a quantum spin Hall phase can be realized at different filling factors. Upon the inclusion of the staggered potential, we also discuss the effect of the time-reversal symmetry breaking term on the stability of the quantum spin Hall state. The variation of the spin-dependent staggered potential is shown to induce the time-reversal symmetry-broken quantum spin Hall phases, and the spin-imbalanced and spin-filtered quantum anomalous Hall phases. The phase transitions are always accompanied by closing of the bulk band gap. We finally demonstrate the edge-state properties of different topological phases.