title: In-gap quasiparticle excitations induced by non-magnetic Cu impurities in Na(Fe(0.96) Co(0.03)Cu(0.01))As revealed by scanning tunnelling spectroscopy.
abstract: The origin of superconductivity in the iron pnictides remains unclear. One suggestion is that superconductivity in these materials has a magnetic origin, which would imply a sign-reversal s(±) pairing symmetry. Another suggests it is the result of orbital fluctuations, which would imply a sign-equal s(++) pairing symmetry. There is no consensus yet which of these two distinct and contrasting pairing symmetries is the right one in iron pnictide superconductors. Here we explore the nature of the pairing symmetry in the superconducting state of Na(Fe0.97-xCo0.03Cux)As by probing the effect of scattering of Cooper pairs by non-magnetic Cu impurities. Using scanning tunnelling spectroscopy, we identify the in-gap quasiparticle states induced by the Cu impurities, showing signatures of Cooper pair breaking by these non-magnetic impurities-a process that is only consistent with s(±) pairing. This experiment provides strong evidence for the s(±) pairing.
authors.affiliation: 1] Center for Superconducting Physics and Materials, National Laboratory of Solid State Microstructures and Department of Physics, National Center of Microstructures and Quantum Manipulation, Nanjing University, Nanjing 210093, China [2].
authors.forename: Huan
authors.initials: H
authors.lastname: Yang
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Wang
authors.forename: Delong
authors.initials: D
authors.lastname: Fang
authors.forename: Qiang
authors.initials: Q
authors.lastname: Deng
authors.forename: Qiang-Hua
authors.initials: QH
authors.lastname: Wang
authors.forename: Yuan-Yuan
authors.initials: YY
authors.lastname: Xiang
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.forename: Hai-Hu
authors.initials: HH
authors.lastname: Wen