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TT: Tiefe Temperaturen

TT 6: Postersitzung I: Josephsonkontakte und SQUIDs, Supraleitung: Theorie, Korrelierte Elektronen, Niederdimensionale Systeme, Magnetotransport, Quantenhalleffekt, Kohlenstoff-Nanoröhrchen, Quantenflüssigkeiten

TT 6.38: Poster

Montag, 26. März 2001, 14:30–17:00, Rang S\ 3

Mixed valent behaviour in edge-shared CuO₂ chain cuprates due to the localization of doped holes — •Z. Hu¹, S.-L. Drechsler¹, J. Malek¹, H. Rosner¹, R. Neudert¹, M. Knupfer¹, M. S. Golden¹, J. Fink¹, J. Karpinski², and G. Kaindl³ — ¹Institute for Solid State Research, IFW Dresden, P.O.Box 270016, D-01171 Dresden, Germany — ²Laboratorium f"ur Festk"orperphysik, ETH Z"urich, CH-8057 Z"urich, Switzerland — ³Institut f"ur Experimentalphysik, Frei Universit"at Berlin, Arnimallee 14, D-14195 Berlin, Germany

We present a joint experimental and theoretical study of the electronic structure of the cuprate chain system A_1−xCuO₂ (A=Ca, Sr, Ba), as measured using O-K and Cu-L₃ X-ray absorption spectroscopy. These systems contain CuO₂ chains built up of edge-sharing CuO₄ plaquettes. The doping dependent behaviour in these systems is radically different to that in conventional 2D cuprate networks formed from corner sharing CuO₄, and follows from the strongly supressed inter-plaquette hybridisation resulting from the 90^o Cu-O-Cu interaction pathway in the chain systems. Spectroscopically, this results in (a) a classical mixed-valent scenario whereby the different final states in the Cu-L₃ spectra can be used directly to ’read-off’ the Cu-valency and (b) a drastic reduction in the dynamic spectral weight transfer from the upper Hubbard band to the low energy scale in the O-K spectra. The final picture emerges of localisation of the doped holes, with the chain then comprised of a mixture of pure Cu(II)0₄ and Cu(III)O₄ plaquettes.