Electronlike Fermi surface in bismuth cuprates determined by ARPES: Bulk versus surface photoemission

We report an extensive angle-resolved photoemission spectroscopy study of a set of quickly dispersing electronic states near the $\Gamma \mathrm{}(0,0)\mathrm{}$ point in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_{2-x}{\mathrm{Ni}}_x{\mathrm{O}}_y\hspace{0.5em}\mathrm{}(x<\mathrm{}1\%)\mathrm{}$ single crystals at photon energy $h\nu =38\mathrm{}$ eV. These states cross the Fermi surface along both the $\Gamma -M$ and $\Gamma -Y$ directions and are outside the well-known large Fermi surface and satellite bands due to the superstructure in Bi2212. The electronic states have a strong nonmonotonic photon energy dependence and demonstrate a symmetry different from the symmetry of the Cu-O plane. The possible origin of these electronic states is discussed. In addition, we show that the whole Fermi-surface topology in Bi2212 is photon energy dependent.