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TT: Fachverband Tiefe Temperaturen

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

TT 3.6: Talk

Monday, March 14, 2011, 12:00–12:15, HSZ 304

Phonon Softening in the CDW Systems NbSe₂ and TiSe₂ — •Roland Hott¹, Rolf Heid¹, Klaus-Peter Bohnen¹, Frank Weber^1,2, Stephan Rosenkranz², John-Paul Castellan², Raymond Osborn², Takeshi Egami³, Ayman Said⁴, and Dmitry Reznik^1,5 — ¹Karlsruhe Institute of Technology, Institute of Solid State Physics, P. O. Box. 3640, D-76021 Karlsruhe, Germany — ²Materials Science Division, Argonne National Laboratory, Argonne, Illinois, 60439, USA — ³Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, 37996, USA — ⁴Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, 60439, USA — ⁵Department of Physics, University of Colorado at Boulder, Boulder, Colorado, 80309, USA

We investigated the soft-mode behaviour of phonons in the Charge Density Wave (CDW) systems NbSe₂ and TiSe₂ both theoretically in Density Functional Theory (DFT) based on ab-initio phonon calculations and experimentally by means of high resolution Inelastic X-ray Scattering (IXS). For both materials, the theoretical predictions for the phonon softening using the experimental lattice parameters coincide with the experimentally observed CDW instability behaviour. While TiSe₂ shows a rather sharp phonon anomaly at T = 190 K, the anomaly in NbSe₂ at T = 33 K is much broader than expected for a Fermi surface nesting driven CDW instability. For NbSe₂, we exclude Fermi surface nesting as main origin of the phonon softening. For TiSe₂, there is no need to go beyond DFT in order to describe the phonon softening.