INVESTIGATION OF THE SPIN-PEIERLS TRANSITION IN CUGEO3 BY RAMAN-SCATTERING

Raman experiments on the Spin-Peierls compound CuGeO3 and the substitu ted (Cu-1-x,Zn-x)GeO3 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 substitutio n-induced disorder. In pure CuGeO3, in addition to normal phonon scatt ering which is not affected at all by the spin-peierls transition, fou r types of magnetic scattering features were observed. Below T-SP = 14 K a singlet-triplet excitation at 30 cm(-1), two-magnon scattering fr om 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 li neshape. 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 t o the behavior of lattice fluctuations recently observed in an electro n diffraction study. This scattering is attributed to dynamical spin-p eierls fluctuations of the weakly or non-static dimerized spin chain.