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TT: Fachverband Tiefe Temperaturen

TT 33: Symposium: High-Temperature Superconductivity

TT 33.12: Vortrag

Donnerstag, 28. Februar 2008, 18:25–18:40, H 0104

Effects of out-of-plane disorder on the superconductivity of Bi₂Sr_2−xLa_xCuO_6+δ — •Jürgen Röhler¹, Christoph Trabant¹, Johanna Frielingsdorf¹, Rabia Djemour¹, Victor Martovitsky², Lenart Dudy³, Helmut Dwelk³, and Alica Krapf³ — ¹Universität zu Köln, 50937 Köln — ²Lebedev-Institute, 119991 Moscow — ³Humboldt Universität zu Berlin, 12489 Berlin

The effects of out-of-plane substitutional order/disorder on cuprate superconductivity remains to a large extent an unresolved issue. We have investigated the connection between superconductivity and the lattice effects arising from the heterovalent doping of Bi₂Sr_2−xLa_xCuO_6+δ, x = 0.8−0.1. Decreasing lanthanum content tunes the compound through the entire underdoped and overdoped regimes. Cu-K and La- K EXAFS served as local structural probes, and single crystal x-ray diffraction for the determination of the basic unit cell, and the symmetry of the supercell. The oxygen atoms in the CuO₂ planes were found significantly disordered, dependent on doping, and to exhibit minimum disorder around x_opt=0.33. But the degree of substitutional disorder in the out-of-plane La environment turned out independent on the concentration of the La dopants, the superstructure symmetry, and the crystal growth parameters, whereas T_c depends sensitively on them. No evidence was found for possible concentration dependent site changes of the La dopant from the nominal Sr to the Bi sites. We discuss the probably crucial role of the interstitial oxygen atoms for the superconducting properties of the Bi₂Sr_2−xLa_xCuO_6+δ system.

Supported by the ESRF through projects HE2473 and HE2644.