Electrical manipulation of plasmon-phonon polaritons in heterostructures of graphene on biaxial crystals

TL;DR

This paper proposes heterostructures of graphene on biaxial crystals to electrically control plasmon-phonon polaritons, enabling tunable infrared nano-optic devices and revealing topological effects.

Contribution

It introduces a theoretical study of hybridized plasmon-phonon polaritons in graphene-biaxial crystal heterostructures with electrical tunability and topological properties.

Findings

Demonstrates wavelength tunability of polaritons

Shows optical topological transitions with Fermi level changes

Reveals tunable quantum spin Hall effects

Abstract

Phonon polaritons in natural anisotropic crystals hold great promise for infrared nano-optics. However, the direct electrical control of these polaritons is difficult, preventing the development of active polaritonic devices. Here we propose the heterostructures of graphene on a biaxial crystal ({\alpha}-phase molybdenum trioxide) slab and theoretically study the hybridized plasmon-phonon polaritons with dependence on the Fermi level of graphene from three aspects: dispersion relationships, iso-frequency contours, and the quantum spin Hall effects. We demonstrate the distinct wavelength tunability of the plasmon-phonon polaritons modes and the optical topologic transitions from open (hyperbolic) to closed (bow-tie-like) iso-frequency contours as the increase of the Fermi level of graphene. Furthermore, we observe the tunable quantum spin Hall effects of the plasmon-phonon polaritons, manifesting propagation direction switching by the Fermi level tuning of the graphene. Our findings open opportunities for novel electrically tunable polaritonic devices and programmable quantum optical networks.