Interplay between Haldane and modified Haldane models in $\alpha$-$T_3$ lattice: Band structures, phase diagrams and edge states

Abstract

We study the topological properties of the Haldane and modified Haldane models in $\alpha$-$T_3$ lattice. The band structures and phase diagrams of the system are investigated. Individually, each model undergoes a distinct phase transition: (i) the Haldane-only model experiences a topological phase transition from the Chern insulator ($\mathcal{C}=1$) phase to the higher Chern insulator ($\mathcal{C}=2$) phase; while (ii) the modified-Haldane-only model experiences a phase transition from the topological metal ($\mathcal{C}=2$) phase to the higher Chern insulator ($\mathcal{C}=2$) phase and we show that $\mathcal{C}$ is insufficient to characterize this system because $\mathcal{C}$ remains unchanged before and after the phase transition. By plotting the Chern number and $\mathcal{C}$ phase diagram, we show that in the presence of both Haldane and modified Haldane models in the $\alpha$-$T_3$ lattice, the interplay between the two models manifests three distinct topological phases, namely the $\mathcal{C}=1$ Chern insulator (CI) phase, $\mathcal{C}=2$ higher Chern insulator (HCI) phase and $\mathcal{C}=2$ topological metal (TM) phase. These results are further supported by the $\alpha$-$T_3$ zigzag edge states calculations. Our work elucidates the rich phase evolution of Haldane and modified Haldane models as $\alpha$ varies continuously from $0$ to $1$ in an $\alpha$-$T_3$ model.

9 pages, 5 figures