Photoemission Evidence for a Remnant Fermi Surface and a d- Wave-Like Dispersion in Insulating Ca 2 CuO 2 Cl 2

Abstract
An angle-resolved photoemission study is reported on Ca2CuO2Cl2, a parent compound of high-T c superconductors. Analysis of the electron occupation probability, n(k), from the spectra shows a steep drop in spectral intensity across a contour that is close to the Fermi surface predicted by the band calculation. This analysis reveals a Fermi surface remnant, even though Ca2CuO2Cl2 is a Mott insulator. The lowest energy peak exhibits a dispersion with approximately the |coskxa – coskya| form along this remnant Fermi surface. Together with the data from Dy-doped Bi2Sr2CaCu2O8+δ, these results suggest that this d-wave–like dispersion of the insulator is the underlying reason for the pseudo gap in the underdoped regime.
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