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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 21.32: Poster

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

Raman Scattering on the S=1/2 Alternating Chain Compound (VO)₂P₂O₇ — •M. Grove¹, P. Lemmens¹, G. Güntherodt¹, and B.C. Sales² — ¹2. Physikalisches Institut, RWTH Aachen, 52056 Aachen — ²Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA

Recently it was shown by inelastic neutron scattering experiments that the compound (VO)₂P₂O₇ is best described as an alternating spin chain with the chains running along b direction [1]. Magnetic triplet excitations have been found with a magnetic zone-center energy gap Δ₀₁=3.1 meV. A second excitation is observed at Δ₁₁=5.8 meV, an energy just below 2Δ₀₁. This mode is interpreted as a triplet two-magnon bound state.

(VO)₂P₂O₇ single crystals have been investigated by means of Raman scattering. At low temperatures (5 K) an additional shoulder appears at 50 cm⁻¹ (6.2 meV) for aa- and bb-polarizations due to two-magnon scattering from the Δ₀₁-branch. We observe a decrease of the scattering intensity at 50 cm⁻¹ on warming up with two temperature regimes. One for 5 K ≤ T ≤ 20 K and another regime for 20 K ≤ T ≤ 55 K (aa-geometry) or 20 K ≤ T ≤ 70 K (2Δ₀₁=72 K) (bb-geometry). In aa-geometry quasielastic scattering due to fluctuations in the spin system can be observed for temperatures above 55 K.
Work supported by DFG through SFB 341 and BMBF Fkz. 13N6586

[1] A.W. Garrett, S.E. Nagler, D.A. Tennant, B.C. Sales, T. Barnes, Phys. Rev. Lett. 79(4), 745 (1997)