Separation of spin and charge excitations in one-dimensionalSrCuO2

In this paper we expand on our earlier results [Phys. Rev. Lett. 77, 4054 (1996)] on angle-resolved photoemission studies on one-dimensional ${\mathrm{SrCuO}}_2$ that reveal a behavior of a hole in Cu-O chain. The results cannot be explained within the conventional band theory, but require a picture in which the spin and charge degrees of freedom for a single electron are separated. Instead of a single branch as predicted in band theory, $E$ versus $k$ relationship can be explained by underlying spinon and holon excitations scaled by hopping energy $t$ and exchange energy $J,$ respectively, indicating separated spin and charge excitations. This is an experimental observation of direct consequence of the spin-charge separation driven by electron correlations that was first predicted thirty years ago. It also shows spinon and holons are real particles with definite energy-momentum dispersions.