Regensburg 2002 – wissenschaftliches Programm

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MA: Magnetismus

MA 14: Schwere Fermionen, Kondo-Systeme II (gemeinsam mit TT)

MA 14.7: Vortrag

Donnerstag, 14. März 2002, 16:00–16:15, H20

Optical conductivity of the clathrate compound Ba6Ge25 — •V. Voevodin1, J. Sichelschmidt1, S. Kimura2, S. Paschen1, W. Carrillo-Cabrera1, Y. Grin1, and F. Steglich11Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str.40, 01187 Dresden — 2Division of Structural Science, Graduate School of Science and Technology Kobe University, Rokkodai, Nada-ku, Kobe 657-8501, Japan

The new clathrate compound Ba6Ge25 is a low charge carrier density system which shows a structural phase change near TS≃200K and gets superconducting at about Tc≃0.24K [1]. The cubic structure consists of large cages of germanium which encapsulate the Ba atoms. Some of the Ba atoms anharmonically vibrate and are locked into split positions below TS≃200K. This behavior crucially effects the properties of the charge carriers which propagate within the framework of cages. Therefore the investigation of the interplay between the phonon modes associated with the Ba atoms and the electronic system is of central interest. We report optical investigations of the electronic properties of Ba6Ge25. Using a broad energy range from 3 meV up to 30 eV our measurements of the optical reflectivity yield a strong temperature dependence of the electronic response near TS≃200K indicating an electronic phase transition.

[1] F.M. Grosche et al., Phys. Rev. Lett. 87(24)(2001)

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