Electronic structure of heavily electron-doped BaFe_1.7Co _0.3AS₂ studied by angle-resolved photoemission

We have performed high-resolution angle-resolved photoemission spectroscopy on heavily electron-doped non-superconducting (SC) BaFe_1.7Co _0.3As₂. We find that the two hole Fermi surface pockets at the Brillouin zone center observed in the hole-doped superconducting Ba _0.6K_0.4Fe₂As₂ are absent or very small in this compound, while the two electron pockets at the zone corner significantly expand due to electron doping by the Co substitution. Comparison of the Fermi surface between non-SC and SC samples indicates that the coexistence of hole and electron pockets connected via the antiferromagnetic wave vector is essential in realizing the mechanism of superconductivity in the iron-based superconductors.