Negative plasmon dispersion in 2H-NbS2 beyond the charge-density-wave interpretation
- Cudazzo, Pierluigi
- Müller, Eric
- Habenicht, Carsten
- Gatti, Matteo
- Berger, Helmuth
- Knupfer, Martin
- Rubio, Angel
- Huotari, Simo
DOIAbstract
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 angstrom(-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...
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