Raman Scattering Study of Phonon and Magnetic Excitations along the Magnetic Chain in CuGeO₃

Detailed temperature dependence of (c, c) Raman scattering spectra has been measured for CuGeO₃ in the vicinity of spin-Peierls transition temperature (T_sp). Below T_sp, six peaks at 30, 105, 227, 370, 416, and 817 cm^-1 have been observed. We newly observed a peak at 416 cm^-1. The energy of the 30 cm^-1 peak decreases continuously with increasing temperature and becomes zero above T_sp. The peak at 30 cm^-1 is assigned as the soft mode in the spin-Peierls phase from the agreement with the temperature dependence of the super-lattice reflection intensity. The peak at 227 cm^-1 is assigned as a two-magnon along the c-axis (Cu chain direction). The peaks at 370, 416, and 817 cm^-1 are assigned as the phonons, which appear by the symmetry change. The new peaks of (c, c) are not sensitive to the magnetic field along the a-axis below 9 T at 4.7 K.