Observation of plasmon-phonon coupling in natural 2D graphene-talc heterostructures

TL;DR

This study investigates mid-infrared nanophotonics in natural talc and graphene-talc heterostructures, revealing tunable phonon resonances and plasmon-phonon coupling, with potential for subwavelength infrared manipulation.

Contribution

It demonstrates for the first time the mid-infrared nanophotonics of talc and its coupling with graphene plasmons, expanding the range of 2D materials for nanophotonic applications.

Findings

Talc resonances can be tuned by crystal thickness.

Graphene plasmons couple with talc phonons, forming hybrid modes.

Gate voltage alters hybridization amplitude.

Abstract

Two-dimensional (2D) materials occupy noteworthy place in nanophotonics providing for subwavelength light confinement and optical phenomena dissimilar to those of their bulk counterparts. In the mid-infrared, graphene-based heterostructures and van der Waals crystals of hexagonal boron nitride (hBN) overwhelmingly concentrate the attention by exhibiting real-space nano-optics from plasmons, phonon-polaritons and hybrid plasmon phonon-polaritons quasiparticles. Here we present the mid-infrared nanophotonics of talc, a natural atomically flat layered material, and graphene-talc (G-talc) heterostructures using broadband synchrotron infrared nano-spectroscopy. We achieve wavelength tuning of the talc resonances, assigned to in- and out-of-plane vibrations by changing the thickness of the crystals, which serves as its infrared fingerprints. Moreover, we encounter coupling of the graphene plasmons polaritons with surface optical phonons of talc. As in the case of the G-hBN heterostructures, this coupling configures hybrid surface plasmon phonon-polariton modes causing 30 % increase in intensity for the out-of-plane mode, blue-shift for the in-plane mode and we have succeeded in altering the amplitude of such hybridization by varying the gate voltage. Therefore, our results promote talc and G-talc heterostructures as appealing materials for nanophotonics, like hBN and G-hBN, with potential applications for controllably manipulating infrared electromagnetic radiation at the subdiffraction scale.