| The temperature dependence of magnetic correlations has been shown to result in an often huge variation of optical spectra even in systems with large charge gaps of several electron volt. This surprising phenomenon provides a unified view on both the magnetic structure and magnetic excitations and on the mechanisms controlling the optical conductivity spectra. This has been investigated in a number of compounds, i.e., ranging from charge fluctuating ladder compounds like NaV2O5 to orbital degenerate systems like LaVO3. Central theme of this contribution is (a) a discussion of the subtleties of multiplet excitations in orbital degenerate systems, and (b) a study of optical spectra of edge-sharing CuO-chain compounds, whose magnetism attracted considerable attention recently because of helical correlations due to frustration. |
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