A mid-infrared biaxial hyperbolic van der Waals crystal

TL;DR

This paper demonstrates that thin flakes of the biaxial van der Waals crystal { extalpha}-MoO3 naturally support in-plane hyperbolic polariton modes at mid-infrared frequencies, enabling advanced light manipulation without complex patterning.

Contribution

It reveals that { extalpha}-MoO3's biaxial hyperbolic properties allow for natural in-plane hyperbolic polaritons, simplifying fabrication of planar photonic devices.

Findings

{ extalpha}-MoO3 supports in-plane hyperbolic polaritons at mid-infrared frequencies.

No patterning needed to achieve hyperbolic modes in { extalpha}-MoO3.

Potential for new light manipulation paradigms in photonics.

Abstract

Hyperbolic media have attracted much attention in the photonics community, thanks to their ability to confine light to arbitrarily small volumes and to their use for super-resolution applications. The 2D counterpart of these media can be achieved with hyperbolic metasurfaces, which support in-plane hyperbolic guided modes thanks to nanopatterns which, however, pose significant fabrication challenges and limit the achievable confinement. We show that thin flakes of the van der Waals material {\alpha}-MoO3 can support naturally in-plane hyperbolic polariton guided modes at mid-infrared frequencies without any patterning. This is possible because {\alpha}-MoO3 is a biaxial hyperbolic crystal, with three different Restrahlen bands, each for a different crystal axis. Our findings can pave the way towards new paradigm to manipulate and confine light in planar photonic devices.