Dispersion Splitting of Phonon Polaritons in van der Waals Heterostructure

TL;DR

This paper demonstrates dispersion splitting of hyperbolic phonon-polaritons in van der Waals heterostructures, enabling advanced dispersion engineering for potential optoelectronic applications.

Contribution

It introduces a novel method of dispersion manipulation via mode hybridization in { extalpha}-MoO3 heterostructures with hBN and graphene, including experimental validation.

Findings

Mode splitting observed in { extalpha}-MoO3 heterostructures using near-field microscopy.

Hybridization leads to two distinct polaritonic branches with different properties.

Proposed Fermi energy tuning in graphene for active dispersion control.

Abstract

The biaxial van der Waals crystal {\alpha}-phase molybdenum trioxide ({\alpha}-MoO3) supports hyperbolic phonon-polaritons with anomalous dispersion in the Type-I Reststrahlen band (RB-I). Despite the low loss and long lifetime of these polaritons, dispersion engineering in this regime has remained largely unexplored. In this work, we show that when two {\alpha}-MoO3 slabs are placed in close proximity, their eigenmodes hybridize and the dispersion splits into two branches with different momenta and field symmetry, providing a powerful platform for dispersion manipulation. We experimentally demonstrate the polaritonic mode splitting in {\alpha}-MoO3 within a heterostructure with hexagonal boron nitride (hBN) employed as a spacer, probed by a scattering-type scanning near-field optical microscope. Furthermore, we propose a design framework for active and mode-selective tailoring of the polaritonic dispersion in the heterostructure incorporating graphene, achieved through tuning its Fermi energy. Our work experimentally demonstrates the feasibility of phonon-polariton mode splitting in the RB-I and suggests a new platform for dispersion engineering of hyperbolic phonon-polaritons in general.