Intra-band and Inter-band Plasmons in Transition Metal Dichalcogenide-Graphene van der Waals Heterostructures

TL;DR

This paper investigates the optical conductivity and plasmonic behavior in graphene-transition metal dichalcogenide heterostructures, revealing conditions for intra-band and inter-band plasmons and their tunability via gate voltage and surrounding materials.

Contribution

It provides new insights into the plasmon dispersion, especially the emergence of acoustic plasmons under specific dielectric environments and doping conditions in GrTMD heterostructures.

Findings

Intra-band plasmon dispersion follows an unconventional q2/3 behavior.

Acoustic plasmons appear when the heterostructure is surrounded by negative dielectric constant materials.

Gate voltage influences intra-band absorbance and inter-band transmittance.

Abstract

In an earlier work, it was shown that the dispersion of the van der Waals heterostructures (vdWHs) of graphene monolayer on 2D transition metal dichalcogenide (GrTMD) substrate comprises of the spin-split, gapped bands. Using these it was also shown that the intra-band plasmon dispersion for the finite doping and the long wavelength limit involves the q2/3 (unconventional) behaviour and not the well known q1/2 behaviour. In this paper the optical conductivity and the optical properties of this vdWH are reported. We find that there are no (inter-band) plasmons for electron doping as long as the Gr-TMD hetero-structure is surrounded by the positive dielectric constant materials above and below. However, if the heterostructure is surrounded by negative dielectric constant (NDC) materials, one finds that there would be acoustic plasmons. For the hole doping case NDC material is not required. We find that the gate voltage tunable intra-band acoustic plasmons also emerge when the carrier density is greater than a moderately critical value. The stronger incarceration capability of GrTMD plasmon compared to that of doped graphene is another notable outcome of the present work. One finds that the intra-band absorbance is decreases with the frequency at a given gate voltage and increases with the gate voltage at a given frequency; the inter-band transmittance, however, is a decreasing function of frequency and the gate voltage.