Anomalous high-energy dispersion in angle-resolved photoemission spectra from the insulating cuprate Ca2CuO2Cl2 -: art. no. 094518

Angle-resolved photoelectron spectroscopic measurements have been performed on an insulating cuprate Ca2CuO2Cl2. High-resolution data taken along the Gamma to the (pi, pi) cut show an additional dispersive feature that merges with the known dispersion of the lowest binding energy feature, which follows the usual strongly renormalized dispersion of approximate to 0.35 eV. This higher energy part reveals a dispersion that is very close to the unrenormalized band predicted by band theory. A transfer of spectral weight from the low energy feature to the high energy feature is observed as the Gamma point is approached. By comparing with theoretical calculations the high energy feature observed here demonstrates that the incoherent portion of the spectral function has significant structure in momentum space due to the presence of various energy scales.