Dresden 2011 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 3: CE: Charge Density Wave \& Peierls Instability
TT 3.6: Vortrag
Montag, 14. März 2011, 12:00–12:15, HSZ 304
Phonon Softening in the CDW Systems NbSe2 and TiSe2 — •Roland Hott1, Rolf Heid1, Klaus-Peter Bohnen1, Frank Weber1,2, Stephan Rosenkranz2, John-Paul Castellan2, Raymond Osborn2, Takeshi Egami3, Ayman Said4, and Dmitry Reznik1,5 — 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.