Dopant-Bound Spinons in Cu_(1-x)Zn_xGeO_3
  Polarized inelastic light scattering experiments on Cu_(1-x)Zn_xGeO_3 (0<= x <= 0.045) single crystals show for x<>0 a new distinct mode at nearly half the energy of the singlet response below the spin-Peierls transition. The temperature, magnetic field, polarization, and doping dependencies of this mode are similar to those of the singlet bound state. The data are interpreted in terms of a spinon-assisted light scattering process. Position and form of the peak provide strong evidence for the presence of dopant-bound spinons in Cu_(1-x)Zn_xGeO_3. 
G. Els, G.S. Uhrig, P. Lemmens, H. Vonberg, P.H.M. van Loosdrecht, G.   Guentherodt, O. Fujita, J. Akimitsu, G. Dhalenne, A....