F. Ronning et al., Photoemission evidence for a remnant fermi surface and a d-wave-like dispersion in insulating Ca2CuO2Cl2, SCIENCE, 282(5396), 1998, pp. 2067-2072
An angle-resolved photoemission study is reported on Ca2CUO2Cl2, a parent c
ompound of high-T-c superconductors. Analysis of the electron occupation pr
obability, 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 c
alculation. This analysis reveals a Fermi surface remnant, even though Ca2C
uO2Cl2 is a Mott insulator. The Lowest energy peak exhibits a dispersion wi
th approximately the \cosk(x)a - cosk(y)a\ form along this remnant Fermi su
rface. Together with the data from Dy-doped Bi2Sr2CaCu2O8+delta, these resu
lts suggest that this d-wave-like dispersion of the insulator is the underl
ying reason for the pseudo gap in the underdoped regime.