Current spinon-holon description of the one-dimensional charge-transfer   insulator SrCuO2: Angle-resolved photoemission measurements
  We have investigated the low-energy electronic structure of the strongly correlated one-dimensional copper oxide chain compound SrCuO2 by angle resolved photoemission as a function of excitation energy. In addition to the prominent spinon-holon continuum we observe a peaklike and dispersive feature at the zone boundary. By fine-tuning the experimental parameters we are able to monitor the full holon branch and to directly measure the electronic hopping parameter with unprecedented accuracy. 
A. Koitzsch, S. V. Borisenko, J. Geck, V. B. Zabolotnyy, M. Knupfer,   J. Fink, P. Ribeiro, B. Buechner, R. Follath