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TT: Fachverband Tiefe Temperaturen

TT 27: CE: Poster Session

TT 27.1: Poster

Mittwoch, 24. März 2010, 14:00–18:00, Poster D1

Soft-Mode Behaviour of Phonons in the CDW Systems NbSe₂ and TiSe₂ — •Roland Hott¹, Rolf Heid¹, Klaus-Peter Bohnen¹, Frank A. Weber², Stephan Rosenkranz², John-Paul A. Castellan², and Ray Osborn² — ¹Karlsruhe Institute of Technology, Institut für Festkörperphysik, P.O.Box 3640, D-76021 Karlsruhe — ²Neutron & X-ray Scattering Group, Materials Science Division, Argonne National Laboratory, 9700 S Cass Ave, Argonne, IL, 60439

We investigated the soft-mode behaviour of phonons in the CDW systems NbSe₂ and TiSe₂ both theoretically in DFT-based ab-initio phonon calculations and experimentally by means of X-ray scattering. For NbSe₂, our calculations predict the development of a phonon instability on reduction of the thermal broadening of the electronic states, in good agreement with the experimental findings. For TiSe₂, our theoretical description correctly indicates a softening of the phonon dispersions in the experimentally observed critical regions of the Brillouin zone. However, the effect predicted here by our DFT-description appears to be too weak to explain the experimentally observed CDW instability.