We report angle resolved photoemission measurements on Sr2CuO2Cl2, an insulating layered copper oxide. We map the energy-momentum dispersion of the highest energy band. We find that the width of this band is consistent with calculations based on variations of the Hubbard model. The dispersion in some directions and the position of the valence band maximum at ( π 2, π 2) match predictions of the t - J model. However the overall shape of the band differs from these predictions. A comparison of our data with spectra previously reported on metallic samples leads to surprising new suggestions for the phenomenology of doping.
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Acknowledgements-We would like to acknowledghee lpfulc onver-sationsw ith P. W. Anderson,V . Emery,E . Dagotto,R . B. Laugh-lin, I? A. Lee and D. J. Scalapino.W e thank D. S. Dessauf or help with the experimentasle t up and P. Blakesleefo r assistance in characterizintgh e crystalsS. SRL is operatedb y the DOE Office of Basic Energy ScienceD, ivision of ChemicalS ciencesT.h e work at Stanfordw as supportedb y DOE Division of Materials ScienceN, SF grant DMR9357057,a nd the StanfordC enterfor MaterialsR esearchT. he work at M.I.T. was supportedb y NSF grantsn umberD MR90-22933a nd DMR93-15715.
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