Materials science

Graphene

Graphene nanoribbons

Superlattice

Surface plasmon

Nano-

Nanophotonics

Surface plasmon polariton

Photonic crystal

Photonics

Polariton

Physics

Nanotechnology

Bilayer graphene

Optics

Condensed matter physics

Composite material

Plasmon

Optoelectronics

Science

Graphene is an atomically thin plasmonic medium that supports highly confined plasmon polaritons, or nano-light, with very low loss. Electronic properties of graphene can be drastically altered when it is laid upon another graphene layer, resulting in a moir\'e superlattice. The relative twist angle between the two layers is a key tuning parameter of the interlayer coupling in thus obtained twisted bilayer graphene (TBG). We studied propagation of plasmon polaritons in TBG by infrared nano-imaging. We discovered that the atomic reconstruction occurring at small twist angles transforms the TBG into a natural plasmon photonic crystal for propagating nano-light. This discovery points to a pathway towards controlling nano-light by exploiting quantum properties of graphene and other atomically layered van der Waals materials eliminating need for arduous top-down nanofabrication.

Photonic crystals for nano-light in moiré graphene superlattices