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TT: Tiefe Temperaturen

TT 22: Postersitzung III: Supraleitende Anwendungen (1-4) Massive HTSL, Bandleiter, Filme (5-26), Transport in HTSL (27-30), Elektronenstruktur in Supraleitern (31-43), Borkarbide (44-50), Quantenphasen- und Metall-Isolator-Überg
änge (51-69)

TT 22.29: Poster

Donnerstag, 30. März 2000, 14:00–17:30, A

Paramagnetic moments and carrier delocalization in nanostructured Bi-Sr-Ca-Cu-O — •S. Skwirblies, H. Jin, F. Wiekhorst, and J. Kötzler — Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung, Universität Hamburg

On nanocrystalline materials, which were grown by annealing of amorphous Bi₂Sr₂CaCu₂O_8+δ at low temperatures, we studied electron spin resonance (ESR), magnetic dc-susceptibility χ(T), and the electrical dc-conductivity σ(T). With incrasing size of the nanocrystals (up to 50nm), which are of pure Bi₂Sr₂CaCu₂O_6+δ-phase, the concentration of paramagnetic Cu²⁺-moments, g_ESR=1.15(2), rapidly decreases accompanied by the onset of a variable-hopping type σ(T) and of a Pauli-susceptibility. We attribute these features to (i) the delocalization of the Cu²⁺ -moments in the nanocrystals and (ii) the random electrical coupling between them by the remains of the weakly conducting, amorphous parent phase.