Angle-Resolved Photoemission Spectroscopy of the Iron-Chalcogenide Superconductor Fe1.03Te0.7Se0.3: Strong Coupling Behavior and the Universality of Interband Scattering

We have performed angle-resolved photoemission spectroscopy of the iron-chalcogenide superconductor Fe1.03Te0.7Se0.3 to investigate the electronic structure relevant to superconductivity. We observed a holelike Fermi surface (FS) and an electronlike FS at the Brillouin zone center and corner, respectively, which are nearly nested by the Q similar to (pi, pi) wave vector. We do not find evidence for the nesting instability with Q similar to (pi + delta, 0) reminiscent of the antiferromagnetic order in the parent compound Fe1+yTe. We have observed an isotropic superconducting (SC) gap along the holelike FS with the gap size Delta of similar to 4 meV (2 Delta/k(B)T(c) similar to 7), demonstrating the strong-coupling superconductivity. The observed similarity of low-energy electronic excitations between iron-chalcogenides and iron-arsenides strongly suggests that common interactions which involve Q similar to (pi, pi) scattering are responsible for the SC pairing.