Local destruction of superconductivity by non-magnetic impurities in mesoscopic iron-based superconductors

The determination of the pairing symmetry is one of the most crucial issues for the iron-based superconductors, for which various scenarios are discussed controversially. Non-magnetic impurity substitution is one of the most promising approaches to address the issue, because the pair-breaking mechanism from the non-magnetic impurities should be different for various models. Previous substitution experiments demonstrated that the non-magnetic zinc can suppress the superconductivity of various iron-based superconductors. Here we demonstrate the local destruction of superconductivity by non-magnetic zinc impurities in Ba 0.5 K 0.5 Fe 2 As 2 by exploring phase-slip phenomena in a mesoscopic structure with 119 × 102 nm 2 cross-section. The impurities suppress superconductivity in a three-dimensional ‘Swiss cheese’-like pattern with in-plane and out-of-plane characteristic lengths slightly below ∼1.34 nm. This causes the superconducting order parameter to vary along abundant narrow channels with effective cross-section of a few square nanometres. The local destruction of superconductivity can be related to Cooper pair breaking by non-magnetic impurities. The pairing symmetry of the wavefunction in high- T c iron-based superconductors remains not completely understood. To shed light on this problem, here the authors investigate the local destruction of superconductivity by introducing Zn impurities in the BKZn iron arsenide compound.