Gate-tunable negative refraction of mid-infrared polaritons

TL;DR

This paper demonstrates gate-tunable negative refraction of mid-infrared polaritons in van der Waals heterostructures, enabling active control and nanoscale focusing for infrared applications.

Contribution

It introduces a novel method using hybrid topological polaritons in atomically thin heterostructures for tunable negative refraction in the mid-infrared range.

Findings

Visualized wide-angle negative refraction of surface polaritons.

Achieved planar nanoscale focusing down to 1.6% of wavelength.

Outperformed bulk materials by reducing scattering losses.

Abstract

Negative refraction provides an attractive platform to manipulate mid-infrared and terahertz radiation for molecular sensing and thermal radiation applications. However, its implementation based on available metamaterials and plasmonic media presents challenges associated with optical losses, limited spatial confinement, and lack of active tunability in this spectral range. Here, we demonstrate gate-tunable negative refraction at mid-infrared frequencies using hybrid topological polaritons in van der Waals heterostructures with high spatial confinement. We experimentally visualize wide-angle negatively-refracted surface polaritons on {\alpha}-MoO3 films partially decorated with graphene, undergoing planar nanoscale focusing down to 1.6% of the free-space wavelength. Our atomically thick heterostructures outperform conventional bulk materials by avoiding scattering losses at the refracting interface while enabling active tunability through electrical gating. We propose polaritonic negative refraction as a promising platform for infrared applications such as electrically tunable super-resolution imaging, nanoscale thermal manipulation, and molecular sensing.