Bilayer Photonic Graphene

Drawing inspiration from the twisted bilayer graphene (TBG), we introduce a photonic bilayer analog consisting of two stacked graphene-like photonic crystals (PC) that support spoof surface plasmons. Beyond the twisting degree of freedom, the associated photonic dispersion can be controlled via the interlayer coupling strength that is readily tunable by varying the air-gap size between the two PCs. We numerically and experimentally characterize the band structures of AA and AB-stacked bilayer PC (BPC), as well as for the cases of sublattice exchanges (SE) with even and odd symmetries. Furthermore, we numerically predict the existence of magic angles in BPC, which are associated with ultra-flat bands resulted from interlayer hybridization. Finally, we uncover the topological corner mode within the topological band-gap associated with the SE even BPC. The proposed BPC could constitute a useful platform for identifying new quantum materials and stimulating the development of next-generation photonic devices with new degrees of freedom.