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TT: Tiefe Temperaturen
TT 21: Symposium Frustrated Systems
TT 21.9: Fachvortrag
Montag, 7. März 2005, 17:35–18:00, TU H104
Spectroscopic studies on geometrically frustrated Na1−xCoO2 — •J. Geck1, T. Kroll1, S.V. Borisenko1, J. Fink1, A.A. Kordyuk1, M. Knupfer1, C. Heß1, C. Sekar1, G. Krabbes1, C. Lin2, H. Berger3, and B. Büchner1 — 1Leibniz Institute for Solid State and Materials Research IFW Dresden, Germany — 2Max Planck Institute for Solid State Research in Stuttgart, Germany — 3Institute of Physics of Complex Matter Lausanne, Suisse
The investigation of strongly correlated electrons in geometrically frustrated lattices is one of the hot topics in current condensed matter research. For instance, the startling discovery of superconductivity in water-intercalated Na1−xCoO2 attracted a great deal of attention. The sodium cobaltites contain triangluar CoO2 sheets, leading to a topological frustration which favors unconventional electronic ground states. In addition to this, there is evidence that the spin-orbit and the crystal-field splitting in these materials are comparable, i.e. unusual coupled spin-orbital excitations might be relevant. Since low energy excitations still remain unclear, it is essential to characterize the electronic system in detail. We have performed angle resolved photoemission, as well as x-ray absorption and photoemission studies on Na1−xCoO2 single crystals with x=0.3,0.5, and 0.7. Our data reveal a low spin configuration of cobalt at all temperatures, a strongly temperature dependent narrow quasiparticle band as well an anisotropic Fermi-velocity. The spectral weight transfer of the XAS spectra as a function of x is interpreted in terms of a Hubbard model.