Electron-energy-loss and time-dependent density functional theory study on the plasmon dispersion in 2H-NbS2

Abstract

We examine the experimental and theoretical electron-energy loss spectra in 2$H$-Cu${}_{0.2}$NbS${}_2$ and find that the 1 eV plasmon in this material does not exhibit the regular positive quadratic plasmon dispersion that would be expected for a normal broad-parabolic-band system. Instead we find a nearly non-dispersing plasmon in the momentum-transfer range $q<0.35$ Å${}^{-1}$. We argue that for a stoichiometric pure 2$H$-NbS${}_2$ the dispersion relation is expected to have a negative slope as is the case for other transition-metal dichalcogenides. The presence of Cu impurities, required to stabilize the crystal growth, tends to shift the negative plasmon dispersion into a positive one, but the doping level in the current system is small enough to result in a nearly-non-dispersing plasmon. We conclude that a negative-slope plasmon dispersion is not connected with the existence of a charge-density-wave order in transition metal dichalcogenides.

References in corpus (4)

• Fermi surface nesting and the origin of Charge Density Waves in metals
• Two energy gaps and Fermi surface 'arcs' in NbSe2
• Pseudogap and charge density waves in two dimensions
• Electron Energy-Loss Spectroscopy: A versatile tool for the investigations of plasmonic excitations

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• Investigation of potassium-intercalated bulk MoS${}_2$ using transmission electron energy-loss spectroscopy
• Plasmon Engineering in Intercalated 2H-TaS${}_2$