Review Article, Physics Reports 376, 1-103 (2003). This article developed from the "first authors" Habilitation and is available here - as a complete preprint version (2002), subm. to Phys. Reports, - as the habilitation manuscript (2000), subm. to the RWTH Aachen.   See here for further information on Peter Lemmens interests, activities and other recent work   See here for the webpage of the IIA. Physikalisches Institut, RWTH Aachen, Germany and its head Gernot Güntherodt   See here for further information on Claudius Gros and his interests and other recent activities.

 

Habilitation, P. Lemmens Handed in on Feb. 1999 at the "Mathematisch-Naturwissenschaftliche Fakultät, der RWTH Aachen", accepted for the "venia legendi" on Feb. 2000. Internal and external referees:  - G. Güntherodt (RWTH Aachen) - W. Metzner (MPI-Stuttgart) - B. Lüthi (Universität Frankfurt) - M. Sigrist (ETH-Zürich) Abstract: In this article recent progress in magnetic light scattering in one-and two-dimensional quantum spin systems is reviewed. These systems received considerable interest from both theoretical and experimental points of view. Following the investigations of the two-dimensional superconducting cuprates and the search for related transition metal oxides a fascinating field of copper oxide compounds, vanadates, manganites and nickelates opened up. These compounds show effects of strong electronic correlations and in particular magnetism in low dimensions. One of the most significant aspects of light scattering experiments is the observation of magnetic bound states. These states originate from strong triplet-triplet interaction and characterize the excitation spectrum of the spin system. Recent theoretical progress has enabled a more detailed understanding of these effects. Parameters like dimerization, frustration, interchain coupling, and spin-phonon coupling have an important impact on the ground state and the excitations of a quantum spin system. After a brief description of the excitations and the phase diagram of quantum spin systems given in Chapter 1, important low-dimensional spin systems, recent experimental results and their interpretations are discussed in Chapter 2. Up to now no comprehensive review on this rapidly growing field exists that also considers material aspects. Therefore I tried to balance between well established results and recent developments. Chapter 3 addresses the theory of magnetic light scattering in low-dimensional spin systems including experimental results on frustration-induced light scattering in the spin-Peierls compound CuGeO3. The following Chapters 4 and 5 discuss magnetic bound states and quasielastic scattering. Chapter 6 finally sums up some aspects of the present knowledge in this field and gives an outlook to future developments.   - Habilitation, P. Lemmens, version 1.3, July 2000