Floquet-Engineered Valley-Topotronics in Kekul\'e-Y Bond Textured Graphene Superlattice

Abstract

The exquisite distortion in a Kekul\'e-Y (Kek-Y) superlattice merges the two inequivalent Dirac cones (from the $K$- and the $K^\prime$- points) into the highest symmetric $\Gamma$-point in the hexagonal Brillouin zone. Here we report that a circularly polarised light not only opens up a topological gap at the $\Gamma$-point but also lifts the valley degeneracy at that point. Endowed with Floquet dynamics and by devising a scheme of high-frequency approximation, we have proposed that the handedness (left/right) in polarised light offers the possibility to realise the valley-selective circular dichroism in Kek-Y shaped graphene superlattice. Also, the non-vanishing Berry curvature and enumeration of valley resolved Chern number $\mathcal{C}_{K}/\mathcal{C}_{K^\prime}=+1/-1$ enable us to assign two pseudo-spin flavors (up/down) with the two valleys. Thereby, the above observations confirm the topological transition suggesting the ease of realising the valley quantum anomalous Hall (VQAH) state within the photon-dressed Kek-Y. These findings further manifest a non-zero optical valley polarisation which is maximum at the $\Gamma$-point. Our paper thus proposes an optically switchable topological valley filter which is desirous in the evolving landscape of valleytronics.