Fresnel aperture diffraction: A phase-sensitive probe of the pairing symmetry of a superconductor

Fresnel single aperture diffraction (FSAD) is proposed as a phase-sensitive probe for pairing symmetry and Fermi surface of a superconductor. We consider electrons injected, through a small aperture, into a thin superconducting (SC) layer. It is shown that in case of SC gap symmetry Δ(-k_x,k _?)=Δ(k_x,k_?) with k_x and k _? respectively the normal and parallel components of the electron Fermi wave vector, the quasiparticle FSAD pattern developed at the image plane is zeroth-order minimum if k_xx=nπ (n is an integer and x is SC layer thickness). In contrast, if Δ(-k_x,k_?)=- Δ(k_x,k_?), the corresponding FSAD pattern is zeroth-order maximum. Observable consequences are discussed for iron-based superconductors of complex multiband pairings.