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

MPS-Authors
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Rubio,  A.
Theory Group, Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
Nano-Bio Spectroscopy Group and European Theoretical Spectroscopy Facility (ETSF), Universidad del País Vasco CFM CSIC-UPV/EHU-MPC DIPC;

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1603.03486.pdf
(Preprint), 159KB

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Citation

Cudazzo, P., Müller, E., Habenicht, C., Gatti, M., Berger, H., Knupfer, M., et al. (2017). Electron-energy-loss and time-dependent density functional theory study on the plasmon dispersion in 2H-NbS2.


Cite as: http://hdl.handle.net/21.11116/0000-0001-E83C-7
Abstract
We examine the experimental and theoretical electron-energy loss spectra in 2H-Cu0.2NbS2 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 \AA−1. We argue that for a stoichiometric pure 2H-NbS2 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.