X-ray absorption of and : Competition between bipolaronic and charge-density wave statesM. Merz1, N. Nücker2, S. Schuppler2, D. Arena3, J. Dvorak4, Y. U. Idzerda4, S. N. Ustinovich5, A. G. Soldatov5, S. V. Shiryaev5 and S. N. Barilo5
1 Institut für Kristallographie, RWTH Aachen Jägerstraße 17-19, D-52066 Aachen, Germany
2 Forschungszentrum Karlsruhe, Institut für Festkörperphysik D-76021 Karlsruhe, Germany
3 Naval Research Laboratory, Code 6345 - Washington, DC 20375, USA
4 Department of Physics, Montana State University - Bozeman, MT 59717-3840, USA
5 Institute of Solid State and Semiconductor Physics, Academy of Sciences Minsk 220072, Belarus
received 14 June 2005; accepted in final form 30 August 2005
published online 21 September 2005
Bulk-sensitive O 1s near-edge X-ray absorption spectroscopy on and single crystals shows for undoped a distinct charge-density wave derived band slightly above the Fermi level; upon K doping it is effectively reduced and competes with bipolaronic hole states whose spectral weight increases with K content. For Pb doping, on the other hand, a wide Pb-O band is formed near EF while the intensity of the bipolaronic hole band remains unaffected. The data suggest a crucial role of hole bipolarons for bismuthate superconductivity.
74.25.Jb - Electronic structure of bulk materials.
74.20.Mn - Nonconventional mechanisms.
78.70.Dm - X-ray absorption spectra.
© EDP Sciences 2005