Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 21: Symposium Frustrated Systems

TT 21.8: Fachvortrag

Montag, 7. März 2005, 17:10–17:35, TU H104

Raman spectroscopy on frustrated spin systems — •Peter Lemmens — Inst. for Solid State Physics, TU Braunschweig, D-38106 Braunschweig, Germany and MPI for Solid State Research, D-70569 Stuttgart, Germany

Many transition metal oxides realize competing interactions based on spin, charge or orbital degrees of freedom (1). Raman scattering has contributed to the understanding of this interplay and the effect of frustration to a great extend due to its unprecedented sensitivity, resolution and additional symmetry information that may be gained considering selection rules. It will be discussed how ground state degeneracy and / or suppressed long range magnetic ordering due to novel spin topologies effect the excitation spectrum of a quantum spin system. Respective model systems are the tetrahedral cluster compound Cu₂Te₂O₅Br₂ and the frustrated dimer system SrCu₂(BO₃)₂. These compounds demonstrate a cross over from low energy singlet bound states to longitudinal magnons. In addition, multiband effects and polarons will be addressed in the hydrated superconductor Na_xCoO₂ yH₂O. This work was supported by DFG SPP1073 and INTAS 01-278.

[1] Spin - Orbit - Topology, a triptych, P. Lemmens and P. Millet, in "Quantum Magnetism", Ed. U. Schollwöck, J. Richter, B.J.J. Farell, R.F. Bishop, Springer, Heidelberg (2004).