Active Tuning of Highly Anisotropic Phonon Polaritons in Van der Waals Crystal Slabs by Gated Graphene

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 properties of these PhPs are intrinsically dictated by 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 tuned 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.

Automated summary

This study reports on a new technology that actively tunes anisotropic Phonon polaritons (PhPs) supported by biaxial vdW slabs by simply gating an integrated graphene layer. Excitingly, the study demonstrates active tuning of optical topological transitions, enabling control of PhPs canalization along different directions.