Probing Topological signatures in an optically driven $\alpha$-${T_3}$ Lattice

TL;DR

This paper investigates how circularly polarized light induces topological phase transitions in an $oldsymbol{ extalpha}$-$T_3$ lattice, revealing changes in Berry curvature, orbital magnetization, and Hall responses across a critical parameter value.

Contribution

It demonstrates the topological phase transition in the $ extalpha$-$T_3$ lattice driven by off-resonant light, with detailed analysis of Berry phase effects and quantized Hall responses.

Findings

Berry curvature and orbital magnetic moment change sign at $oldsymbol{ extalpha=1/\sqrt{2}}$

Orbital magnetization slopes relate to Chern numbers, indicating a topological transition

Quantized Hall conductivity differs on either side of the critical $oldsymbol{ extalpha}$ value

Abstract

The $\alpha$-$T_3$ lattice, an interpolation model between the honeycomb lattice of graphene($\alpha=0$) and the dice lattice($\alpha=1$), undergoes a topological phase transition across $\alpha=1/\sqrt{2}$ when exposed to a circularly polarized off-resonant light. We study Berry phase mediated bulk magnetic and anomalous thermoelectric responses in order to capture the topological signatures of a driven $\alpha$-$T_3$ lattice. It is revealed that both the Berry curvature and the orbital magnetic moment associated with the flat band change their respective signs across $\alpha=1/\sqrt{2}$. The off-resonant light distorts the flat band near the Dirac points when $0<\alpha<1$ which eventually introduces two distinct well separated forbidden gaps of equal width in the quasienergy spectrum. The orbital magnetization varies linearly with the chemical potential, in the forbidden gaps. The slopes of the linear regions in the orbital magnetization are closely related to the respective Chern numbers on either side of $\alpha=1/\sqrt{2}$. We find that the slope for $\alpha>1/\sqrt{2}$ is approximately two times of that for $\alpha<1/\sqrt{2}$ which essentially indicates a topological phase transition across $\alpha=1/\sqrt{2}$. However, the anomalous Nernst coefficient vanishes when the chemical potential is tuned in the forbidden gaps. The anomalous Hall conductivity in the forbidden gap(s) approaches different quantized values on either side of $\alpha=1/\sqrt{2}$. All these topological signatures can be observed experimentally.