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TT: Tiefe Temperaturen

TT 11: Postersitzung II (Metall-Isolator-Überg
änge, Phasenüberg
änge in Quantensystemen, Theorie: Systeme korrelierter Elektronen)

TT 11.31: Poster

Dienstag, 25. März 2003, 14:30–19:00, P2c, P2d

Observation of a longitudinal magnon in the tetrahedral quantum spin system Cu₂Te₂O₅Br₂ — •Claudius Gros¹, P. Lemmens^2,3, M. Vojta⁴, Roser Valenti¹, K. -Y. Choi², H. Kageyama⁵, Z. Hiroi⁵, N.V. Mushnikov⁵, T. Goto⁵, M. Johnsson⁶, and P. Millet⁷ — ¹Fakultät 7, Theoretische Physik, Universität des Saarlandes — ²2. Physikalisches Institut, RWTH Aachen — ³MPI for Solid State Research, Stuttgart — ⁴ITKM, Universität Karlsruhe — ⁵ISSP, Kashiwa, Japan — ⁶Dept. of Inorg. Chem., Stockholm, Sweden — ⁷CEMES/CNRS, Toulouse, France

We present a comprehensive study of the coupled tetrahedra-compound Cu₂Te₂O₅Br₂ by theory and experiments in external magnetic fields. We report the observation of a longitudinal magnon in Raman scattering in the ordered state close to quantum criticality. We show that the excited tetrahedral-singlet sets the energy scale for the magnetic ordering temperature T_N. This energy is determined experimentally. The ordering temperature T_N has an inverse-log dependence on the coupling parameters near quantum criticality.