Active tuning of highly anisotropic phonon polaritons in van der Waals crystal slabs by gated graphene

TL;DR

This paper demonstrates active control of highly anisotropic phonon polaritons in van der Waals crystal slabs by gating graphene, enabling dynamic manipulation of light propagation and topological transitions for advanced optoelectronic applications.

Contribution

It introduces a method to actively tune anisotropic phonon polaritons in vdW slabs using gated graphene, allowing dynamic control of optical topological transitions.

Findings

Gating graphene enables active tuning of phonon polaritons.

Control over topological transitions affects PhP canalization.

Potential for developing tunable optoelectronic devices.

Abstract

Phonon polaritons (PhPs) -- lattice vibrations coupled to electromagnetic fields -- in highly anisotropic media display a plethora of intriguing optical phenomena (including ray-like propagation, anomalous refraction, and topological transitions, among others), which have potential for unprecedented manipulation of the flow of light at the nanoscale. However, the propagation properties of these PhPs are intrinsically linked to the anisotropic crystal structure of the host material. Although in-plane anisotropic PhPs can be steered (and even canalized) by twisting individual crystal slabs in a van der Waals (vdW) stack, active control of their propagation via external stimuli presents a significant challenge. Here, we report on a technology in which anisotropic PhPs supported by biaxial vdW slabs are actively tunable by simply gating an integrated graphene layer. Excitingly, we predict active tuning of optical topological transitions, which enable controlling the canalization of PhPs along different in-plane directions in twisted heterostructures. Apart from their fundamental interest, our findings hold promises for the development of optoelectronic devices (sensors, photodetectors, etc.) based on PhPs with dynamically controllable properties.