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 Ca 2 CuO 2 Cl 2 , 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 Ca 2 CuO 2 Cl 2 is a Mott insulator. The lowest energy peak exhibits a dispersion with approximately the |cos k x a – cos k y a | form along this remnant Fermi surface. Together with the data from Dy-doped Bi 2 Sr 2 CaCu 2 O 8+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.