Plasmons in metallic monolayer and bilayer transition metal dichalcogenides

Abstract

We study the collective electronic excitations in metallic single-and bilayer transition metal dichalcogenides (TMDCs) using time dependent density functional theory in the random phase approximation. For very small momentum transfers (below q ≈ 0.02 Å−1 ) the plasmon dispersion follows the √ q behavior expected for free electrons in two dimensions. For larger momentum transfer the plasmon energy is significantly red shifted due to screening by interband transitions. At around q ≈ 0.1 Å−1 the plasmon enters the dissipative electron-hole continuum and the plasmon dispersions flatten out at an energy around 0.6-1.1 eV, depending on the material. Using bilayer NbSe2 as example, we show that the plasmon modes of a bilayer structure take the form of symmetric and anti-symmetric hybrids of the single-layer modes. The spatially anti-symmetric mode is rather weak with a linear dispersion tending to zero for q = 0 while the energy of the symmetric mode follows the single-layer mode dispersion with a slight blue shift.

Valley plasmonics in transition metal dichalcogenides

“…On the one side there are models combining effective k · p descriptions of the quadratic electronic bands around the band gap with an evaluation of the dielectric function within the random phase approximation 29,30 . On the other side, there are RPA descriptions based on full density functional theory calculations, which include realistic single particle band structures describing the complete Brillouin zone 32,[38][39][40][41][42] . Here, we add a third approach by utilizing a materialspecific low-energy model Hamiltonian derived from ab initio calculations for the undoped material as the basis for the evaluation of dynamical response functions in the electron and hole doped situations.…”

Interplay between structure and electronic properties of layered transition-metal dichalcogenides: Comparing the loss function of1Tand2Hpolymorphs

“…[23], this property is related to the depolarization effect induced by crystal local fields. Finally, in the optical limit q < 0.02Å −1 , the plasmon frequency has a √ q dispersion [31].…”

Plasmons on the edge ofMoS2nanostructures

“…Localized surface plasmon resonances (LSPR) in metal nanoparticles have been utilized for chemical sensing [1], cancer treatment [2], and to increase solar cell performance [3]. Two-dimensional (2D) plasmons are found at metal surfaces and thin films [4], in graphene [5][6][7][8], and other atomically thin 2D materials such as metallic transition metal dichalcogenides [9].…”