  We propose a trilayer $\pi$-junction that takes advantage of the
unconventional $s_{x^2 y^2}=\cos k_x \cos k_y$ pairing symmetry which changes
sign between electron and hole Fermi pockets in the iron pnictides. In
addition, we also present theoretical results for Andreev bound states in thin
superconductor-normal metal (or insulator) iron-pnictide junctions. The
presence of nontrivial in-gap states, which uniquely appear in this
unconventional pairing state, is a distinct feature in comparison to other
singlet pairing states.
