Europhys. Lett.
Volume 72, Number 2, October 2005
Page(s) 275 - 281
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 21 September 2005
Europhys. Lett., 72 (2), pp. 275-281 (2005)
DOI: 10.1209/epl/i2005-10236-6

X-ray absorption of $\chem{Ba_{1- \it x}K_{\it x}BiO_{3}}$ and $\chem{BaPb_{1-\it y}Bi_{\it y}O_{3}}$: Competition between bipolaronic and charge-density wave states

M. 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 $\chem{Ba_{1- \it x}K_{\it x}BiO_{3}}$ and $\chem{BaPb_{1-\it y}Bi_{\it y}O_{3}}$ single crystals shows for undoped $\chem{BaBiO_{3}}$ 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