Fermi energy band dispersion and orbital symmetry of Bi2Sr2CaCu2Oy studied by non-polarized-light two-dimensional photoelectron spectroscopy

To study the two-dimensional Fermi energy band dispersion of Bi2Sr2CaCu2Oy in the vicinity of the Fermi level, photoelectron intensity angular distributions (PIADs) was measured at room temperature using non-polarized He I excitation light (21.2 eV) in normal incidence geometry. Strong photoelectron peaks appeared at the M¯ points in the PIAD at the Fermi level. They are attributed to the Fermi energy band which disperses toward both the Γ and Z points at higher binding energies, however, only the dispersion from the M¯ toward the Z points with increasing binding energy was observed. The disappearance of photoelectron peaks of Fermi energy band in the first Brillouin zone was explained by the transition matrix element from dx2-y2 atomic orbital to p and f final states for the case of non-polarized light at normal incidence.