High-Resolution Angle-Resolved Photoemission Studies of High T

An angle-resolved photoemission study of the normal and superconducting states in Bi_2Sr _2CaCu_2O _8 was performed. Measurements in the normal state show bands dispersing through the Fermi level from at least 350 meV below E_{F }. The Fermi level crossings are consistent with local-density band calculation, including a point calculated to be of Bi-O character. Additional measurements were made where bands crossed the Fermi level between 100 and 250K, along with measurements on an adjacent Pt foil. The Fermi edges of both materials agree to within the noise. Below the Fermi level, the spectra show correlation effects in the form of an increased effective mass. The shape of the spectra can be explained by a lifetime-broadened photohole and secondary electrons. The effective inverse photohole lifetime is linear in energy. A superconducting gap has been measured at a number of points where there is density at the Fermi level in the normal state. By proper modeling, a gap of 24 meV was obtained for all these points, including points of Cu-O and Bi-O character respectively, according to band calculation. The lack of gap anisotropy in the basal plane suggests that pairing in this material is not d-wave pairing.