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Statut |
Confirmé |
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Série |
SEM-BESSON |
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Domaines |
cond-mat |
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Date |
Lundi 21 Novembre 2011 |
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Heure |
10:30 |
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Institut |
IMPMC |
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Salle |
salle de conférence, 4ème Etage, couloir 22-23 |
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Nom de l'orateur |
Weber |
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Prenom de l'orateur |
Frank |
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Addresse email de l'orateur |
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Institution de l'orateur |
Karlsruher Institut für Technologie Institut für Festkörperphysik |
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Titre |
Phonon softening and charge density wave formation in nbse2 and tise2 |
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Résumé |
We report [1] inelastic x-ray scattering measurements of the temperature
dependence of phonon dispersion in the prototypical charge-density-wave (CDW)
compounds NbSe2 and TiSe2. Surprisingly, acoustic phonons in NbSe2 soften to
zero frequency and become overdamped over an extended region around the CDW
wavevector. This extended phonon collapse is dramatically different from the sharp
cusp in the phonon dispersion expected from Fermi surface nesting. Instead, our
experiments combined with ab initio calculations, show that it is the wavevector
dependence of the electron-phonon coupling that drives the CDW formation in
NbSe2 and determines its periodicity. For TiSe2 [2], we found theoretically that the
above described electron-phonon coupling scenario is able to stabilize a CDW
ground state as well. Calculations of the lattice dynamical properties are in good
agreement with our experimental results for the soft phonon dispersion and
linewidth. A more detailed analysis of the calculations yield wavevector dependent
matrix elements, strong enough to stabilize the CDW order in combination with an
enhanced electronic joint density of states at the ordering wavevector.
1 F. Weber et al., Physical Review Letters 107 (10), 107403 (2011).
2 F. Weber, et al. http://arXiv.org/abs/1105.3292 (2011). |
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Numéro de preprint arXiv |
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Commentaires |
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Fichiers attachés |
- seminWEBER2011.pdf (150416 bytes)
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