Low-energy magnetic excitations in the dimerized and incommensurate phase of CuGeO3

Low-energy magnetic excitations in the dimerized (D) and incommensurate (I) phase of CuGeO3 were studied by Raman spectroscopy. Based on temperature a nd magnetic field dependent experiments on pure and Si-doped samples the Ra man peak ac 17 cm(-1) for T = 2 K in the D-phase is attributed to a soliton -assisted one-magnon excitation. We further present a Raman-study of the lo w-energy spin dynamics of a spin-Peierls system in the incommensurate phase . The magnetic field induced transition between D- and I-phase of CuGeO3 (B -c greater than or similar to 12.5 T) is characterized by the appearance of an intense new low-energy mode. For the incommensurate phase a finite zone -center excitation gap of Delta = 2.3 +/- 0.2 cm(-1) is deduced. (C) 1999 P ublished by Elsevier Science Ltd. All rights reserved.