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TT: Fachverband Tiefe Temperaturen

TT 3: CE: Charge Density Wave \& Peierls Instability

TT 3.8: Talk

Monday, March 14, 2011, 12:30–12:45, HSZ 304

Electron Energy-Loss Spectroscopy on the Transition-Metal Dichalchogenide 2H-TaSe₂ — •Andreas König¹, Roman Schuster², Helmuth Berger³, Martin Knupfer¹, and Bernd Büchner¹ — ¹IFW Dresden, Institute for Solid State Research, P. O. Box 270116, D-01171 Dresden, Germany — ²Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland — ³Insitut de Physique de la Matière Complexe, EPFL, CH-1051 Lausanne, Switzerland

2H-TaSe₂ is one of the various polytypes of the transition-metal dichalchogenide (TMDC) TaSe₂. It consists of hexagonal layers with weak interlayer van-der-Waals bonding. It shows phase transitions to a charge-density wave (CDW) and to a superconducting state. Although there is strong evidence for the competition of these two ordering effects as well as for a Peierls transition scenario for the origin of the CDW, a theoretical understanding of the mechanism leading to the phase transitions is still subject of discussions. What is already proved for 2H-TaSe₂ and a few other TMDCs is a negative dispersion of the bulk plasmon in the normal state and an even larger bandwidth of this negative dispersion in the CDW state, which is altogether not a behavior of a common metal. Furthermore, the slope of the plasmon dispersion is doping dependent. We performed Electron Energy-Loss Spectroscopy in transmission on thin films of 2H-TaSe₂ for different potassium contents as well as for different temperatures above and below the CDW transition temperature to investigate the connection of the CDW phase transition to the plasmon dispersion.