title: Graphene on hexagonal boron nitride as a tunable hyperbolic metamaterial.
abstract: Hexagonal boron nitride (h-BN) is a natural hyperbolic material, in which the dielectric constants are the same in the basal plane (ε(t) ≡ ε(x) = ε(y)) but have opposite signs (ε(t)ε(z) < 0) in the normal plane (ε(z)). Owing to this property, finite-thickness slabs of h-BN act as multimode waveguides for the propagation of hyperbolic phonon polaritons--collective modes that originate from the coupling between photons and electric dipoles in phonons. However, control of these hyperbolic phonon polaritons modes has remained challenging, mostly because their electrodynamic properties are dictated by the crystal lattice of h-BN. Here we show, by direct nano-infrared imaging, that these hyperbolic polaritons can be effectively modulated in a van der Waals heterostructure composed of monolayer graphene on h-BN. Tunability originates from the hybridization of surface plasmon polaritons in graphene with hyperbolic phonon polaritons in h-BN, so that the eigenmodes of the graphene/h-BN heterostructure are hyperbolic plasmon-phonon polaritons. The hyperbolic plasmon-phonon polaritons in graphene/h-BN suffer little from ohmic losses, making their propagation length 1.5-2.0 times greater than that of hyperbolic phonon polaritons in h-BN. The hyperbolic plasmon-phonon polaritons possess the combined virtues of surface plasmon polaritons in graphene and hyperbolic phonon polaritons in h-BN. Therefore, graphene/h-BN can be classified as an electromagnetic metamaterial as the resulting properties of these devices are not present in its constituent elements alone.
authors.affiliation: Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: S
authors.initials: S
authors.lastname: Dai
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02215, USA.
authors.forename: Q
authors.initials: Q
authors.lastname: Ma
authors.affiliation: 1] Department of Physics, University of California, San Diego, La Jolla, California 92093, USA [2] Department of Physics, Stony Brook University, Stony Brook, New York 11794-3800, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Liu
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02215, USA.
authors.forename: T
authors.initials: T
authors.lastname: Andersen
authors.affiliation: Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: Z
authors.identifier: 0000000200090507
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: Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: M
authors.initials: M
authors.lastname: Wagner
authors.affiliation: National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: K
authors.identifier: 0000000337018119
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: M
authors.initials: M
authors.lastname: Thiemens
authors.affiliation: Ludwig-Maximilians-Universität and Center for Nanoscience, 80539 München, Germany.
authors.forename: F
authors.identifier: 0000000183342310
authors.initials: F
authors.lastname: Keilmann
authors.affiliation: Micro and Nano Engineering Lab, Department of Precision and Microsystems Engineering, TU Delft, Mekelweg 2, 2628 CD Delft, The Netherlands.
authors.forename: G C A M
authors.initials: GC
authors.lastname: Janssen
authors.affiliation: Micro and Nano Engineering Lab, Department of Precision and Microsystems Engineering, TU Delft, Mekelweg 2, 2628 CD Delft, The Netherlands.
authors.forename: S-E
authors.identifier: 0000000218177811
authors.initials: SE
authors.lastname: Zhu
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02215, USA.
authors.forename: P
authors.initials: P
authors.lastname: Jarillo-Herrero
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