title: Effect of charge order on the plasmon dispersion in transition-metal dichalcogenides.
abstract: We investigate the dispersion of the charge carrier plasmon in the three prototypical charge-density wave bearing transition-metal dichalcogenides 2H-TaSe(2), 2H-TaS(2), and 2H-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 observed in simple metals as well as the related system 2H-NbS(2), which does not exhibit charge order. We present a semiclassical Ginzburg-Landau model which accounts for these observations, and argue that the vicinity to a charge ordered state is thus reflected in the properties of the collective excitations.
authors: Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors: Jasper
authors: J
authors: van Wezel
authors: Roman
authors: R
authors: Schuster
authors: Andreas
authors: A
authors: König
authors: Martin
authors: M
authors: Knupfer
authors: Jeroen
authors: J
authors: van den Brink
authors: Helmuth
authors: H
authors: Berger
authors: Bernd
authors: B
authors: Büchner