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TT: Tiefe Temperaturen

TT 24: Postersitzung III: Korrelierte Elektronen, ”Orbital Physics”

TT 24.49: Poster

Mittwoch, 10. März 2004, 14:30–19:00, Poster A

Giant phonon anomalies in the pseudo-gap phase of TiOCl — •P. Lemmens^1,2, K.-Y. Choi², G. Caimi³, L. Degiorgi^3,4, A. Seidel⁵, and F.C. Chou⁵ — ¹MPI for Solid State Research, D-70569 Stuttgart — ²2. Physikalisches Institut, D-52056 RWTH Aachen — ³Laboratorium für Festkörperphysik, ETH Zürich, CH-8093 Zürich — ⁴Paul Scherrer Institute, CH-5232 Villigen — ⁵Center for Material Science and Engineering, MIT, Cambridge, MA 02139

We report infrared and Raman spectroscopy results of the spin-1/2 quantum magnet TiOCl. Giant anomalies are found in the temperature dependence of the phonon spectrum, which hint to unusual coupling of the electronic degrees of freedom to the lattice. These anomalies develop over a broad temperature interval, suggesting the presence of an extended fluctuation regime. This defines a pseudo-gap phase, characterized by a local spin-gap. Below 100 K a dimensionality cross-over leads to a dimerized ground state with a global spin-gap of about 2Δ_spin≈ 430 K. Work supported by the DFG SPP1073, MRSEC Program of NSF under award number DMR 02-13282, NATO PST.CLG.9777766, INTAS 01-278, and the Swiss National Foundation for the Scientific Research.