Modal properties of a cylindrical graphene-coated nanowire deposited on a hexagonal boron nitride substrate.

Due to complementary chemical and optical characteristics, structural integration of graphene and hexagonal boron nitride (hBN) can lead to a promising platform for development of novel plasmonic devices. In this paper, we numerically investigate the modal behavior of a cylindrical graphene-coated nanowire (GNW) deposited on a thin hBN (GNW-hBN) substrate in the mid-infrared range. Our studies revealed that GNW-hBN can support hybridized plasmon-phonon modes in the upper reststrahlen band of hBN, which mainly originates from the strong coupling between plasmon modes in GNW and phonon modes in hBN. The characteristics of these hybrid modes can be effectively tuned by changing the chemical potential of graphene, hBN thickness, and gap distance between GNW and hBN. According to the results, by choosing smaller gap distances and tuning the chemical potential of graphene, GNW-hBN can exhibit a fundamental mode (m=0, where m is the azimuthal mode number) with higher effective index such that Real(n) varies from 131.2-62.3 when the hBN thickness changes from 2-20 nm. In addition, the presence of an hBN slab can break the azimuthal symmetry of the high-order graphene plasmon modes (m≥1) in the GNW-hBN structure.