Tunable topological valley plasmons in graphene/hexagonal boron nitride moire superlattices

Moir\'e superlattices constructed by stacking two two-dimensional (2D) materials offer a natural platform for exploring fascinating topological photonics scenarios, owing to the large lattice periodicity and unique electronic structures, which help to overcome the limitations of artificial photonic structures imposed by fabrication techniques. In this study, we demonstrate the potential of the 2D moir\'e superlattice formed by graphene and hexagonal boron nitride, a promising 2D photonic material, in supporting topological valley plasmons. Our calculations reveal that, by adjusting the Fermi level of the superlattice, interband transitions of electrons can be suppressed, facilitating the emergence of low-loss valley plasmons with wave vectors reaching the corners of the moir\'e Brillouin zone. These plasmons carry opposite valley Chern numbers in the $K$ and ${K}^{\ensuremath{'}}$ valleys, displaying scattering-resistant topological protected boundary states. Moreover, the frequency gap of the valley plasmons can be tuned by varying the position of the Fermi level or applying a compressive strain along the out-of-plane direction. Our findings offer a strategy for realizing more miniaturized and tunable topological photonic devices.