Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 7: Focused Session: Resonant Inelastic X-ray Scattering on Magnetic Excitations
TT 7.4: Topical Talk
Montag, 26. März 2012, 17:20–18:00, H 0104
Excitons as a probe for low-energy spin fluctuations in cuprate chains — •Jochen Geck1, Valentina Bisogni1, Claude Monney2, Kejin Zhou2, Roberto Kraus1, Jiri Malek1, Stefan-Ludwig Drechsler1, and Thorsten Schmitt2 — 1Leibniz Institute for Solid State and Materials Research, Dresden, Germany — 2Paul Scherrer Institute, Villigen, Switzerland
High-resolution RIXS provides outstanding capabilities for studying the spin, charge and orbital dynamics in correlated electron materials. Focussing on one-dimensional cuprates, a short overview of recent experiments will be presented, which illustrates that soft RIXS is a unique probe for collective spin and orbital excitations in such systems. However, low-energy excitations below 10meV are currently not directly accessible with this technique, due to the limited energy resolution of about 100meV. In this talk, we will present an experimental approach that circumvents this limitation. Using a charge transfer exciton as a probe, we show that local spin fluctuations at excitation energies of the order of 1meV can be detected with great sensitivity. Two prototypical edge-sharing cuprate chain materials with different magnetic intra-chain order have been studied in this way, namely CuGeO3 (AFM) and Li2CuO2 (FM). For the latter, the FM intra-chain spin order is confirmed, but strong AFM spin fluctuations are still observed well below the magnetic ordering temperature. This reveals that Li2CuO2 is close to a quantum critical point. The presented method provides an excellent tool to characterize new one-dimensional cuprate materials and to search for novel magnetic ground states.