Normal-state Fermi surface of pristine and Pb-doped Bi2Sr2CaCu2O8+δ from angle-resolved photoemission measurements and its photon energy independence

We address the question as to whether the topology of the normal-state Fermi surface of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$—as seen in angle-resolved photoemission—depends on the photon energy used to measure it. High-resolution photoemission spectra and Fermi-surface maps from pristine and Pb-doped ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ are presented, recorded using both polarized and unpolarized radiation of differing energies. The data show clearly that no main band crosses the Fermi surface along the $\Gamma \overline{M}Z$ direction in reciprocal space, even for a photon energy of 32 eV, thus ruling out the existence of a Γ-centered, electronlike Fermi surface in this archetypal high-$T_C$ superconductor. The true topology of the normal-state Fermi surface remains that of holelike barrels centered at the $X,Y$ points of the Brillouin zone.