Neutron spectroscopy in RBa2Cu3Ox (R=rare earth; 6≤x≤7) and R2-xCexCuO4-δ (0≤x≤0.2) compounds: charge transfer, cluster formation, percolative superconductivity, charge fluctuations
✍ Scribed by A. Furrer; P. Allenspach; F. Fauth; M. Guillaume; W. Henggeler; J. Mesot; S. Rosenkranz
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 303 KB
- Volume
- 235-240
- Category
- Article
- ISSN
- 0921-4534
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✦ Synopsis
Neutron spectroscopic experiments performed for the high-Tc superconducting hole-doped RBa2Cu3Ox (R=rare earth; 6_<x<7) and electron-doped R2_xCexCuO4-~i (~_x_<0.2) compounds are discussed. In these systems the R ions are situated close to the superconducting CuO2 planes, thus the crystal-field interaction at the R site constitutes an ideal local probe of the charge distribution and thereby monitors directly changes of the carder concentration induced by doping. For several compounds the observed crystal-field spectra separate into different local components whose spectral weights distinctly depend on the doping level, i.e., there is clear experimental evidence for cluster formation. The onset of superconductivity can be shown to result from percolation, i.e., the superconductivity is an inhomogeneous property in the persovskite-type compounds. From a line-width analysis of the observed crystal-field transitions we derive the evolution of the fractal sizes of the clusters versus doping. At high doping the neutron spectroscopic data reveal anomalies which are interpreted in terms of copper-oxyde charge fluctuations.