Fresnel Aperture Diffraction: A Phase-sensitive Probe For Pairing Symmetry Of A Superconductor

Recently iron-based superconductor has been observed, not only with high T_c (56 k), but also has multiple characteristics of high Tc copper-oxide superconductor. Different materials has shown that the similar characteristics of superconductor, it will provid more clues for superconducting mechanism. The pairing symmetry of electron is the core issue to reveal the superconducting mechanism. However, the same samples of iron-based superconducting is measured in different experiments with different symmetry. Fresnel single aperture diffraction (FSAD) is proposed as a phase-sensitive probe for Fermi surface and pairing symmetry of a superconductor. And we used the theory of BTK and BdG equations solved the Andreev equation. On this basis, we discussed the pairing symmetry of superconductors.Firstly, we introduced the research background, significance and research at home and abroad status.Secondly, FSAD is proposed as a phase-sensitive probe for Fermi surface and pairing symmetry of a superconductor. It is shown that in case of gap symmetry△(-k)=△(k) with k the wavevector of electrons tunneling into an normal-insulator-superconductor (NIS) junction of a thin superconducting layer, the quasiparticle FSAD pattern developed at r is zeroth-order minimum if k·r=nπ(n is an integer). In contrast, for the case of△(-k)=-△(k) , the corresponding FSAD pattern is zeroth-order maximum. So we can take the advantage of this simple experimental to test the pairing symmetry of a superconductor.Thirdly, Observable consequences are discussed and suggested for probing the iron-based superconductor to which gap symmetry may be complex as a result of multiple Fermi surface pairing.