All-angle negative refraction of highly squeezed plasmon and phonon polaritons in graphene-boron nitride heterostructures

TL;DR

This paper demonstrates that strong coupling in graphene-BN heterostructures enables all-angle negative refraction of highly squeezed polaritons, paving the way for advanced nanophotonic applications like superlenses and nanoscale imaging.

Contribution

It reveals that hybrid plasmon-phonon polaritons in graphene-BN heterostructures can achieve negative refraction at all angles, a novel mechanism for manipulating light at the nanoscale.

Findings

Negative refraction predicted between plasmon and phonon polaritons.

Negative refraction also predicted between hybrid graphene plasmons.

Strong coupling enables flipping the group velocity sign of polaritons.

Abstract

A fundamental building block for nanophotonics is the ability to achieve negative refraction of polaritons, because this could enable the demonstration of many unique nanoscale applications such as deep-subwavelength imaging, superlens, and novel guiding. However, to achieve negative refraction of highly squeezed polaritons, such as plasmon polaritons in graphene and phonon polaritons in boron nitride (BN) with their wavelengths squeezed by a factor over 100, requires the ability to flip the sign of their group velocity at will, which is challenging. Here we reveal that the strong coupling between plasmon and phonon polaritons in graphene-BN heterostructures can be used to flip the sign of the group velocity of the resulting hybrid (plasmon-phonon-polariton) modes. We predict all-angle negative refraction between plasmon and phonon polaritons, and even more surprisingly, between hybrid graphene plasmons, and between hybrid phonon polaritons. Graphene-BN heterostructures thus provide a versatile platform for the design of nano-metasurfaces and nano-imaging elements.