Laser induced Flqouet topological phases in a 2D weak topological insulator with unconventional nonlinear dispersion

Abstract

Recently, we presented a two-dimensional (2D) model of a weak topological insulator formed by stacking an N number of Su-Schrieffer-Heeger (SSH) chains \cite{Agrawal_2022-02}. We now study the influence of periodic driving on the topological properties of this system, which has all the fundamental symmetries, by shining it with circularly polarized light (CPL). The CPL is chosen because it breaks the time-reversal symmetry, which induces more exotic topological properties in the system. We investigate two different formations of the N stacked SSH chains: all the SSH chains are topologically trivial in one formation and nontrivial in the other one. In contrast to the undriven or static case, both formations exhibit distinct topological behaviors. Here, we particularly derive the Floquet or the effective Hamiltonian using the replica method, which facilitates the study of high- and low-frequency regimes. We have discovered that this model exhibits laser-induced Floquet topological phases with higher Chern numbers. This system has nonlinear dispersion along both directions with additional kx−ky coupling terms, which made the dispersion of this system {\it unconventional}. We closely study the role of this unconventional dispersion in the system at the low-energy limit and its response to periodic driving. The low-energy Hamiltonian also reveals a hierarchy in the gaps of the neighboring Floquet bands. Interestingly, though this model has nonlinear quasi-energy dispersion, it still shows some signatures of hierarchy, which was observed in the system with linear dispersion like graphene. Furthermore, we study the effect of linearly polarized light (LPL) on the topological properties of the system. In response to the LPL driving, the band-touching point either opens up or splits into two band-touching points.