Tunable coupling of terahertz Dirac plasmons and phonons in transition metal dicalchogenide-based van der Waals heterostructures

TL;DR

This paper investigates how the coupling between Dirac plasmons in graphene and phonons in transition metal dichalcogenides within van der Waals heterostructures can be tuned, revealing regimes of strong and ultra-strong coupling.

Contribution

It introduces a realistic simulation approach and a semiclassical theory to analyze and predict tunable plasmon-phonon coupling in vdW heterostructures.

Findings

Coupling strength depends on TMD layer number and composition.

Strong and ultra-strong coupling regimes are achievable.

Tuning graphene's Fermi energy controls the coupling regime.

Abstract

Dirac plasmons in graphene hybridize with phonons of transition metal dichalcogenides (TMDs) when the materials are combined in so-called van der Waals heterostructures (vdWh), thus forming surface plasmon-phonon polaritons (SPPPs). The extend to which these modes are coupled depends on the TMD composition and structure, but also on the plasmons' properties. By performing realistic simulations that account for the contribution of each layer of the vdWh separately, we calculate how the strength of plasmon-phonon coupling depends on the number and composition of TMD layers, on the graphene Fermi energy and the specific phonon mode. From this, we present a semiclassical theory that is capable of capturing all relevant characteristics of the SPPPs. We find that it is possible to realize both strong and ultra-strong coupling regimes by tuning graphene's Fermi energy and changing TMD layer number.