Floquet engineering of topological phase transitions in quantum spin Hall $\alpha$-$T_{3}$ system

TL;DR

This paper explores how high-frequency circularly polarized light can induce and control topological phase transitions in the quantum spin Hall $ extalpha$-$T_{3}$ system, revealing new topological phases and edge states.

Contribution

It demonstrates Floquet engineering as a method to realize novel topological phases in $ extalpha$-$T_{3}$ lattices, including spin-polarized metallic phases and the effects of a staggered potential.

Findings

Identification of spin-polarized topological metallic phases

Dependence of topological invariants on band occupation with staggered potential

Control of topological phase transitions via off-resonant light

Abstract

Floquet engineering of topological phase transitions driven by a high-frequency time-periodic field is a promising approach to realizing new topological phases of matter distinct from static states. Here, we theoretically investigate Floquet engineering topological phase transitions in the quantum spin Hall $\alpha$-$T_{3}$ system driven by an off-resonant circularly polarized light. In addition to the quantum spin (anomalous) Hall insulator phase with multiple helical (chiral) edge states, spin-polarized topological metallic phases are observed, where the bulk topological band gap of one spin sub-band overlaps with the other gapless spin sub-band. Moreover, with a staggered potential, the topological invariants of the system depend on whether the middle band is occupied because of the breaking of symmetry with respect to the center of energy-momentum plane. Our work highlights the significance of Floquet engineering in realizing new topological phases in $\alpha$-$T_{3}$ lattices.