Low-dimensional quantum spin systems display fascinating excitation spectra. In recent years, optical spectroscopy was shown to be a powerful tool for the study of these spectra by means of phonon-assisted infrared absorption. We discuss the results of antiferromagnetic S=1/2 cuprates with various topologies: the spinon continuum observed in the weakly coupled chains of CaCu2O3, two-triplet bound states and the continuum of the two-leg ladders in (La,Ca)14Cu24O41, and the bimagnon-plus-phonon spectrum of the bilayer YBa2Cu3O6, an undoped parent compound of the 2D high-Tc cuprates. Various theoretical approaches (dynamical DMRG, continuous unitary transformations (CUT), and spin-wave theory) are used for a quantitative analysis. Particular attention is paid to the role of the cyclic four-spin exchange.
CITATION STYLE
Grüninger, M., Windt, M., Benckiser, E., Nunner, T. S., Schmidt, K. P., Uhrig, G. S., & Kopp, T. (2003). Optical Spectroscopy of Low-Dimensional Quantum Spin Systems (pp. 95–112). https://doi.org/10.1007/978-3-540-44838-9_7
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