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. Revcolevschi⁴ — ¹II. 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.