Comparative XANES study on the two electron-doped high-Tc superconductor systems, (Sr,La)CuO2 and (Nd,Ce)2CuO4

✍ Scribed by Y. Tanaka; M. Karppinen; J.M. Chen; R.S. Liu; H. Yamauchi

• Publisher: Elsevier Science
• Year: 2009
• Tongue: English
• Weight: 401 KB
• Volume: 182
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1016/j.jssc.2009.02.014

✦ Synopsis

Here we employ high-quality samples of (Sr 1Àx La x )CuO 2 and (Nd 2Àx Ce x )CuO 4 and XANES spectroscopy at O-K, Cu-L 2,3 and Ce-M 4,5 edges to gain comprehensive understanding of the electronic structure and doping in n-type high-T c superconductors. Not only common but also slightly different features are revealed for the two systems. From O-K-edge spectra, the UHB is found essentially independent of the electron-doping level for both the systems, in line with our understanding that the doped electrons do not go to the O site in n-type copper-oxide superconductors. Another common observation is that the main Cu II peak at the Cu-L 3 edge (due to transitions to the Cu II -3d orbitals) systematically decreases in intensity upon electron doping, hence verifying the fact that the doped electrons go to the Cu site. The difference then between the two systems is that in (Sr 1Àx La x )CuO 2 the weaker Cu II peak due to transitions to the Cu II -4s orbital depends on the degree of doping. Moreover, it was found that with increasing x, electron density increases much faster in (Sr 1Àx La x )CuO 2 than in (Nd 2Àx Ce x )CuO 4 . This is a consequence of two phenomena: a tiny increase in oxygen content concomitant to the Ce IV -for-Nd III substitution and the somewhat lower Ce-valence value of +3.8 compared to the nominal tetravalent state.