The Effect of Charge Order on the Plasmon Dispersion in Transition-Metal Dichalcogenides

TL;DR

This study examines how charge order influences plasmon dispersion in transition-metal dichalcogenides, revealing negative dispersion linked to charge density waves using electron energy-loss spectroscopy and a Ginzburg-Landau model.

Contribution

It provides new insights into the impact of charge order on plasmon behavior in transition-metal dichalcogenides through experimental and theoretical analysis.

Findings

Negative plasmon dispersion in charge-density wave materials

Contrast with simple metals and non-charge-ordered systems

Ginzburg-Landau model explains the observations

Abstract

We investigate the dispersion of the charge carrier plasmon in the three prototypical charge-density wave bearing transition-metal dichalcogenides 2H-TaSe2, 2H-TaS2 and 2H-NbSe2 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 to the generic behavior observed in simple metals as well as the related system 2H-NbS2, 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.