Graphene on hexagonal boron nitride as an agile hyperbolic metamaterial

S. Dai, Q. Ma, S. -E. Zhu, M. K. Liu, T. Andersen, Z. Fei, M. Goldflam, M. Wagner, K. Watanabe, T. Taniguchi, M. Thiemens, F. Keilmann, G. C. A. M. Janssen, P. Jarillo-Herrero, M. M. Fogler, D. N. Basov

Published 2015-01-28Version 1

We have implemented and investigated the tunable hyperbolic response in heterostructures comprised of a monolayer graphene deposited on hexagonal boron nitride (G-hBN) slabs. Electrostatic gating of the graphene layer enables electronic tunability of phonon polaritonic properties of hBN: a layered material with well-documented hyperbolic response in the mid-infrared (mid-IR) frequencies. The tunability originates from the hybridization of surface plasmon polaritons in graphene to hyperbolic phonon polaritons in hBN: an effect that we examined via nano-IR imaging and spectroscopy. The hybrid polaritons possess combined virtues from plasmons in graphene and phonon polaritons in hBN. Therefore, G-hBN structures fulfill the definition of the electromagnetic metamaterial since the attained property of these devices is not revealed by its constituent elements. Our results uncover a practical approach for realization of agile nano-photonic metamaterials by exploiting the interaction of distinct types of polaritonic modes hosted by different constituent layers of van der Waals heterostructures.