Effect Of Impurity Scattering On Order Symmetry Of Fe - Based Superconductors

Since the discovery of the high-temperature superconductivity (HTSC) in copper oxides, despite enormous unprecedented efforts by researchers all over the world, the physical nature of high-temperature superconductivity in cuprates is still not completely understood. Recent discovery of high-temperature superconductivity in iron based compounds has ignited a worldwide burst of activity. This is a new type of compounds with the critical temperature (TC) higher than McMillan limit besides the cuprates. There are important similarities between Fe pnictides and cuprates. Both are layered systems, and both feature close proximity of antiferromagnetic order and superconductivity in their respective phase diagrams. But there are crucial differences as well. Fe-pnictide compounds demand a multiband description and the parent Fe pnictides are semimetals with several electron and hole pockets on the Fermi surface. All these features can help us to have a deeper understanding of the mechanisms of HTSC.In this article, We consider the effect of magnetic impurities, modeled by classical spins, in iron-based superconductors. By using two-band model, we show that one magnetic impurity scattering exhibits pronounced two fold symmetry (C2) in iron-based superconductors. We suggest that these results deserve more attention in the analysis of C2symmetry found in scanning tunneling microscopy experiments for different iron-based superconductors. This paper is organized as follows:In section Ⅰ, we introduce the development of the superconductors firstly. We introduce some important theories and experiments in the developments of the conventional and unconventional superconductors.In section Ⅱ, we introduce the BCS theory.In section Ⅲ, We consider the effect of magnetic impurities, modeled by classical spins, in iron-based superconductors. By using a self-consistent Bogoliubov-de Gennes formalism, we show that one magnetic impurity scattering exhibits pronounced two fold symmetry (C2) in iron-based superconductors. We also study the effects of quantum interference in impurity structures consisting of two magnetic impurities. We show that the quantum interference leads to characteristic signatures of twofold symmetry not only in the local density of states (LDOS), but also in the spatial form of the superconducting order parameter. We suggest that these results deserve more attention in the analysis of C2symmetry found in scanning tunneling microscopy experiments for different iron-based superconductors.