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Berlin 2005 – scientific programme

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.43: Poster

Saturday, March 5, 2005, 11:00–16:30, Poster TU C

Optical spectroscopy of magnetic excitations — •E. Benckiser1, M. Grüninger1, T. Nunner2, T. Kopp2, C. Sekar3, G. Krabbes3, and A. Revcolevschi41II. Physikalisches Institut, Universität zu Köln — 2Experimentalphysik VI, Universität Augsburg — 3IFW Dresden — 4Laboratoire de Physico-Chimie de l’Etat Solides, Universite Paris-Sud, France

The magnetic excitations of several low-dimensional spin systems have been studied systematically by means of phonon-assisted infrared absorption. We present the optical conductivity σ(ω) of the 1D S=1/2 chain compound SrCuO2, of the S=1/2 pseudo-ladder compound CaCu2O3 and of the 2D system Ba2Cu3O4Cl2. CaCu2O3 has been discussed as a two-leg S=1/2 ladder with J ≪ J. A detailed analysis of the optical conductivity shows that CaCu2O3 is rather a 3D system of weakly coupled chains with J ≈ 165 meV, where the two couplings perpendicular to the chains are much weaker but comparable with each other. The compound SrCuO2 contains antiferromagnetic double-chains with J ≈ 181 meV, whereas the inter-chain coupling is weak ferromagnetic and frustrated. The 2D Cu3O4 layers in Ba2Cu3O4Cl2 contain a CuO2 square lattice plus a second Cu square lattice with a much weaker coupling constant J2. For ω ≫ J2 the compound represents a clean realization of an undoped CuO2 layer. We find that the high-energy spectral weight above the 2-magnon peak is larger than assumed previously.

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