Probing Hyperbolic and Surface Phonon-Polaritons in 2D materials using Raman Spectroscopy

TL;DR

This paper demonstrates how Raman spectroscopy can effectively probe hyperbolic phonon-polaritons in 2D materials like GaSe, revealing their dispersion and guiding properties without complex wavevector matching, thus aiding MIR nanophotonics development.

Contribution

It introduces a Raman spectroscopy method for probing hyperbolic phonon-polaritons in 2D materials, simplifying the analysis of their dispersion and confinement properties.

Findings

Raman spectra confirm the existence of surface and guided polaritons.

Dispersion relations are revealed by varying the incidence angle.

Resonant excitation enhances scattering efficiency near excitonic states.

Abstract

The hyperbolic dispersion relation of phonon-polaritons (PhPol) provides high-momentum states, highly directional propagation, subdiffractional confinement, large optical density of states, and enhanced light-matter interactions. In this work, we use Raman spectroscopy in the convenient backscattering configuration to probe PhPol in GaSe, a 2D material presenting two hyperbolic regions separated by a \textit{double} reststrahlen band. By varying the incidence angle, dispersion relations are revealed. Raman spectra calculations confirm the observation of one surface and two extraordinary guided polaritons and matches the evolution of PhPol frequency as a function of confinement. Resonant excitation close to the excitonic state singularly exalts the scattering efficiency of PhPol. Raman spectroscopy of PhPol in non-centrosymmetry 2D materials does not require any wavevector matching strategies. Widely available, it may accelerate the development of MIR nanophotonic devices and applications.