Effect of Charge Order on the Plasmon Dispersion in Transition-Metal Dichalcogenides
Effect of Charge Order on the Plasmon Dispersion in Transition-Metal Dichalcogenides
We investigate the dispersion of the charge carrier plasmon in the three prototypical charge-density wave bearing transition-metal dichalcogenides $2H\mathrm{\text{\ensuremath{-}}}{\mathrm{TaSe}}_{2}$, $2H\mathrm{\text{\ensuremath{-}}}{\mathrm{TaS}}_{2}$, and $2H\mathrm{\text{\ensuremath{-}}}{\mathrm{NbSe}}_{2}$ employing electron energy-loss spectroscopy. For all three compounds the plasmon dispersion is found to be negative for small momentum transfers. This is in contrast with the generic behavior …