Accessing phonon polaritons in hyperbolic crystals by ARPES

TL;DR

This paper proposes using ARPES to access and study phonon-polariton modes in hyperbolic materials like hexagonal boron nitride, revealing their coupling with graphene plasmons through spectral features.

Contribution

It introduces a novel method to probe hyperbolic phonon-polaritons via ARPES by analyzing their coupling with graphene plasmons.

Findings

Predicted ARPES spectral features due to PP modes

Demonstrated coupling between PP modes and graphene plasmons

Provided a new spectroscopic approach for hyperbolic materials

Abstract

Recently studied hyperbolic materials host unique phonon-polariton (PP) modes. The ultra-short wavelengths of these modes, which can be much smaller than those of conventional exciton-polaritons, are of high interest for extreme sub-diffraction nanophotonics schemes. Polar hyperbolic materials such as hexagonal boron nitride can be used to realize strong long-range coupling between PP modes and extraneous charge degrees of freedom. The latter, in turn, can be used to control and probe PP modes. Of special interest is coupling between PP modes and plasmons in an adjacent graphene sheet, which opens the door to accessing PP modes by angle-resolved photoemission spectroscopy (ARPES). A rich structure in the graphene ARPES spectrum due to PP modes is predicted, providing a new probe of PP modes and their coupling to graphene plasmons.