  We have performed high-resolution angle-resolved photoemission spectroscopy
of iron-chalcogenide superconductor Fe1.03Te0.7Se0.3 (Tc = 13 K) to investigate
the electronic structure relevant to superconductivity. We observed a hole- and
an electron-like Fermi surfaces at the Brillouin zone center and corner,
respectively, which are nearly nested by the Q~(pi, pi) wave vector. We do not
find evidence for the nesting instability with Q~(pi+delta, 0) reminiscent of
the antiferromagnetic order in the parent compound Fe1+yTe. We have observed an
isotropic superconducting gap along the hole-like Fermi surface with the gap
size Delta of ~4 meV (2Delta/kBTc~7), demonstrating the strong-coupling nature
of the superconductivity. The observed similarity of low-energy electronic
excitations between iron-chalcogenide and iron-arsenide superconductors
strongly suggests that common interactions which involve Q~(pi, pi) scattering
are responsible for the superconducting pairing.
