Optical Nanoimaging of Hyperbolic Surface Polaritons at the Edges of van der Waals Materials

TL;DR

This paper presents the first near-field optical imaging of hyperbolic surface polaritons at the edges of van der Waals materials, revealing their confinement and guiding properties with potential for future applications.

Contribution

It introduces the experimental observation and imaging of hyperbolic surface polaritons in vdW materials, specifically at the edges, using s-SNOM.

Findings

HSPs exhibit stronger field confinement than volume HPs

HSPs have smaller group velocities

HSPs have nearly identical lifetimes to volume HPs

Abstract

yperbolic polaritons in van der Waals materials recently attract a lot of attention, owing to their strong electromagnetic field confinement, ultraslow group velocities and long lifetimes. Typically, volume confined hyperbolic polaritons (HPs) are studied. Here we show the first near-field optical images of hyperbolic surface polarities, HSPs, which are confined and guided at the edges of thin flakes of a vdW material. To that end, we applied scattering-type scanning near-field optical microscopy (s-SNOM) for launching and real-space nanoimaging of hyperbolic surface phonon polariton modes on a hexagonal boron nitride, h-BN, flake. Our imaging data reveal that the fundamental HSP mode exhibits stronger field confinement, smaller group velocities and nearly identical lifetimes, as compared to the fundamental HP mode of the same h-BN flake. Our experimental data, corroborated by theory, establish a solid basis for future studies and applications of HPs and HSPs in vdW materials.