  We observed the anisotropic superconducting-gap (SC-gap) structure of a
slightly overdoped superconductor, Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$
($x=0.1$), using three-dimensional (3D) angle-resolved photoemission
spectroscopy. Two hole Fermi surfaces (FSs) observed at the Brillouin zone
center and an inner electron FS at the zone corner showed a nearly isotropic SC
gap in 3D momentum space. However, the outer electron FS showed an anisotropic
SC gap with nodes or gap minima around the M and A points. The different
anisotropies obtained the SC gap between the outer and inner electron FSs
cannot be expected from all theoretical predictions with spin fluctuation,
orbital fluctuation, and both competition. Our results provide a new insight
into the SC mechanisms of iron pnictide superconductors.
