Investigation of the Spin-Peierls transition in CuGeO3 by Raman scattering

Raman experiments on the Spin-Peierls compound CuGeO(3) and the substituted (Cu(1-x),Zn(x))GeO(3) and Cu(Ge(1-x),Ga(x))O(3) compounds were performed in order to investigate the response of specific magnetic excitations of the one-dimensional spin-chain to spin anisotropies and substitution-induced disorder. In pure CuGeO(3), in addition to normal phonon scattering which is not affected at all by the spin-peierls transition, four types of magnetic scattering features were observed. Below T(SP) = 14 K a singlet-triplet excitation at 30 cm(-1), two-magnon scattering from 30 to 227 cm(-1) and folded phonon modes at 369 and 819 cm(-1) were identified. They were assigned by their temperature dependence and lineshape. For temperatures between the spin-peierls transition T(SP) and approximately 100 K a broad intensity maximum centered at 300 cm(-1) is observed. The temperature dependence of this intensity is similar to the behavior of lattice fluctuations recently observed in an electron diffraction study. This scattering is attributed to dynamical spin-peierls fluctuations of the weakly or non-static dimerized spin chain.