  We have made a phase-sensitive measurement on the corner junction of the
iron-based superconductor BaFe1.8Co0.2As2, and observed the typical
Fraunhofer-like diffraction pattern. The result suggests that there is no phase
shift between the a-c face and b-c face of a crystal, which indicates that the
superconducting wavefunction of the iron based superconductor is different from
that of a cuprate superconductor.
