Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 15: Superconductivity: Poster Session
TT 15.18: Poster
Dienstag, 26. Februar 2008, 14:00–18:00, Poster B
Raman spectroscopy study of the pyrochlore superconductors KOs2O6 and RbOs2O6 — •Ana Maria Racu1, Joachim Schoenes1, Zbigniev Bukowski2, and Janusz Karpinski2 — 1Institut für Physik der Kondensierten Materie, TU Braunschweig, Germany — 2Laboratorium für Festkörperphysik, ETH Zürich, Switzerland
The discovery of superconductivity in the pyrochlore oxides KOs2O6, RbOs2O6 and CsOs2O6 has attracted much interest due to their unusual properties. Crystallographic studies proposed two different structures whithin the centrosymmetric Fd3m and the non-centrosymmetric Fd43m [1] space groups. Both reveal a very special feature: the alkali atom is situated in an oversized Os-O cage. It is believed that the anharmonic rattling of the alkali atom in the cage strongly influences the electronic structure and the superconductivity [2]. We performed Raman measurements on single crystals of KOs2O6 and RbOs2O6. The experimental results are compared with a factor group analysis for the two proposed crystal structures. The number and the symmetry of the observed modes is compatible with the centrosymmetric space group. In the low energy range we observe a mode which is strongly dependent on the alkali atom. Its energy corresponds to one of the fine structures observed in KOs2O6[3] in the photoemission spectra. We attribute this low energy mode to the Raman active rattling vibration of the K and Rb atoms.
[1] Schuck et al., PRB 73, 144506 (2006)
[2] Hiroi et al., J. Phys. Soc Jpn. 74, 3400 (2005)
[3] Shimojima et al., PRL 99, 117003 (2007)