Optically Controlled Topological Phases in the Deformed $\alpha-T_{3}$ Lattice

Abstract

Haldane's tight-binding model, which describes a Chern insulator in a two-dimensional hexagonal lattice, exhibits quantum Hall conductivity without an external magnetic field. Here, we explore an $\alpha -T_{3}$ lattice subjected to circularly polarized off-resonance light. This lattice, composed of two sublattices (A and B) and a central site (C) per unit cell, undergoes deformation by varying the hopping parameter $\gamma _{1}$ while keeping $\gamma _{2}$= $\gamma _{3}$= $\gamma $. Analytical expressions for quasi-energies in the first Brillouin zone reveal significant effects of symmetry breaking. Circularly polarized light lifts the degeneracy of Dirac points, shifting the cones from M. This deformation evolves with $\gamma _{1} $, breaking symmetry at $\gamma _{1}=2\gamma $, as observed in Berry curvature diagrams. In the standard case ($\gamma _{1}=\gamma $), particle-hole and inversion symmetries are preserved for $\alpha =0$ and $% \alpha =1$. The system transitions from a semi-metal to a Chern insulator, with band-specific Chern numbers: $C_{2}=1$, $C_{1}=0$, and $C_{0}=-1$ for $% \alpha <1/\sqrt{2},$ shifting to $C_{2}=2$, $C_{1}=0$, and $C_{0}=-2$ when $% \alpha \geqslant 1/\sqrt{2}.$For $\gamma _{1}>2\gamma $, the system enters a trivial insulating phase. These transitions, confirmed via Wannier charge centers, are accompanied by a diminishing Hall conductivity. Our findings highlight tunable topological phases in $\alpha -T_{3}$ lattices, driven by light and structural deformation, with promising implications for quantum materials.