Regensburg 1998 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 21: Postersitzung III: Spin-Peierls-Systeme, Metall-Isolator-Übergang, Lokalisierung; SL: Theorie; Quantenflüssigkeiten und -kristalle; Amorphe Materialien, Tunnelsysteme; Borcarbide, Fullerene, konventionelle SL; SL dünner Filme; Experimentiertechniken

TT 21.34: Poster

Donnerstag, 26. März 1998, 15:00–18:30, D

Brillouin Light Scattering on Cu_1−xZn_xGeO₃ — •G. Els¹, P.H.M. van Loosdrecht¹, P. Lemmens¹, H. Vonberg¹, G. Güntherodt¹, G.S. Uhrig², O. Fujita³, J. Akimitsu³, G. Dhalenne⁴, and A. Revcolevschi⁴ — ¹2. Phys. Inst., RWTH Aachen, 52056 Aachen, Germany — ²Inst. für Theor. Phys., Universität Köln, 50937 Köln, Germany — ³Dep. of Physics, Aoyama Gakuin University, Tokyo 157, Japan — ⁴Laboratoire de Chimie des Solides, Université de Paris-Sud, 91405 Orsay, France

Brillouin light scattering has been performed on Cu_1−xZn_xGeO₃ single crystals as a function of temperature (2K<T<20K), magnetic field (0T<H<6T), doping (0<x<4.5%), and polarization.

In undoped CuGeO₃ a thermally activated weak shoulder is observed at roughly 18 cm⁻¹ on the low energy side of the well-known singlet bound state (SBS) at 30 cm⁻¹. The appearance of this shoulder indicates a novel three-magnon light scattering process between excited triplet states.

In Zn-doped CuGeO₃ a different scattering process with a broad but well-defined peak shape is observed below the spin- Peierls transition T_SP. The peak position is at nearly half that of the SBS and has a similar temperature dependence. Its intensity increases continuously upon cooling well below T_SP in contrast to the three-magnon scattering. This new mode can be understood in terms of a bound state of a magnon and a doping-induced undimerized spin.

Work supported by DFG through SFB 341 and BMBF Fkz. 13N6586