title: Plasmons in graphene moiré superlattices.
abstract: Moiré patterns are periodic superlattice structures that appear when two crystals with a minor lattice mismatch are superimposed. A prominent recent example is that of monolayer graphene placed on a crystal of hexagonal boron nitride. As a result of the moiré pattern superlattice created by this stacking, the electronic band structure of graphene is radically altered, acquiring satellite sub-Dirac cones at the superlattice zone boundaries. To probe the dynamical response of the moiré graphene, we use infrared (IR) nano-imaging to explore propagation of surface plasmons, collective oscillations of electrons coupled to IR light. We show that interband transitions associated with the superlattice mini-bands in concert with free electrons in the Dirac bands produce two additive contributions to composite IR plasmons in graphene moiré superstructures. This novel form of collective modes is likely to be generic to other forms of moiré-forming superlattices, including van der Waals heterostructures.
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore.|Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: G X
authors.initials: GX
authors.lastname: Ni
authors.affiliation: State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road Shanghai 200050, China.
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Wu
authors.affiliation: Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Fei
authors.affiliation: Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Goldflam
authors.affiliation: Ludwig-Maximilians-Universität and Center for Nanoscience, 80539 München, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Keilmann
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore.
authors.forename: B
authors.initials: B
authors.lastname: Özyilmaz
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore.
authors.forename: A H
authors.initials: AH
authors.lastname: Castro Neto
authors.affiliation: State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road Shanghai 200050, China.
authors.forename: X M
authors.initials: XM
authors.lastname: Xie
authors.affiliation: Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Fogler
authors.affiliation: Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: D N
authors.initials: DN
authors.lastname: Basov