Photoemission Study of Single Crystal Bi2Sr2CaCu2O8

Photoemission measurements with synchrotron radiation have been performed on single crystal Bi2Sr2CaCu208. Two energy bands with dispersion of 0.2–0.5 eV were observed in the vicinity of the Fermi level and one of them crosses the Fermi level midway between the center and boundary of the Brillouin zone, giving a clear evidence for existence of a Fermi surface. The Fermi-edge peak exhibits a pronounced enhancement at photon energy of the 0 2s core threshold, meaning a dominant 0 2p nature of the Fermi-edge states. These results indicate existence of the Fermi-liquid states with dominant 0 2p nature in the high-Tc superconductor. The superconductivity could be driven by formation of Cooper-pairs of the 0 2p holes in the Fermi-liquid states, probably through the spin or charge fluctuation.