Soliton bound states in the Raman spectrum of pure and doped spin-Peierls chains

We investigate the occurrence of singlet bound states in the Raman spectrum of dimerized spin 1/2 chains by exact diagonalization and density matrix r enormalization-group techniques. We predict that several bulk delta peaks c ould be observed in pure systems. Furthermore, we show that additional low- energy lines arise from nonmagnetic impurity doping. These features are int erpreted in terms of soliton-antisoliton and solitonimpurity bound states, respectively. Energies and spectral weights associated with these bound sta tes are sensitive to lattice relaxation effects. Our results are discussed in the context of the inorganic spin-Peierls compound CuGeO3 and quantitati vely compared to recent Raman experiments. [S0163-1829(99)01526-X].