Manifestation of spin-charge separation in the dynamic dielectric   response of one--dimensional Sr2CuO3
  We have determined the dynamical dielectric response of a one-dimensional, correlated insulator by carrying out electron energy-loss spectroscopy on Sr2CuO3 single crystals. The observed momentum and energy dependence of the low-energy features, which correspond to collective transitions across the gap, are well described by an extended one-band Hubbard model with moderate nearest neighbor Coulomb interaction strength. An exciton-like peak appears with increasing momentum transfer. These observations provide experimental evidence for spin-charge separation in the relevant excitations of this compound, as theoretically expected for the one-dimensional Hubbard model. 
R. Neudert, M. Knupfer, M. S. Golden, J. Fink, W. Stephan, K. Penc, N.   Motoyama, H. Eisaki, and S. Uchida