Raman-scattering study ofCuGeO3in the spin-Peierls phase

Phonons and magnetic excitations were studied as a function of temperature in the spin-Peierls phase of an inorganic material ${\mathrm{CuGeO}}_{3}$ by Raman scattering. All of the phonon Raman peaks observed at room temperature can be assigned on condition that the crystal symmetry is ${\mathit{D}}_{2\mathit{h}}^{5}$(Pbmm). Five peaks intrinsic to the spin-Peierls state were observed at 30, 105, 228, 370, and 818 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in the spin-Peierls phase. The temperature dependence of the frequency of the 30-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ peak agrees approximately with 2\ensuremath{\Delta}(T), where \ensuremath{\Delta}(T) is the spin-Peierls gap. The Raman spectrum between 0 and 300 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ was compared with the density of states of the magnetic excitons. The 105- and 228-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ peaks were assigned to two-magnetic-exciton Raman scattering. The peaks at 370 and 818 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ were assigned to one-phonon Raman scattering of the folded ${\mathit{A}}_{\mathit{g}}$ modes, which occurs due to the formation of a dimerization in the spin-Peierls phase.