Theoretical Study On Local Density Of States Induced By A Magnetic Impurity In Iron-based Superconductors

Superconductivity is a research subject with great application prospect and important scientific significance.The discovery of iron-based superconductors is the important progress in the field of superconductivity.It is shown that iron-based superconductors are a new class of systems whose superconductivity originates from the Cooper pairs of the Fe-Fe plane.The iron-based superconductors also have layered structure and are multi-band superconductors with both hole-and electron-type energy bands.These features can help us to study the mechanism of iron-based high temperature superconductivity.Based on a two-orbit four-band tight-binding model,we have introduced the superconducting mean field Hamiltonian with a single impurity,which can be diagonalized by using the Fourier transform,the canonical transformation,and the Bogoliubov transformation.The local density of states near the impurity point is obtained by employing the Green's function method.Impurity research is one of the important topics in superconductivity.A single magnetic impurity can induce in-gap bound states in iron-based superconductors.Based on the two-orbit four-band tight-binding model,we have investigated the impact of a single magnetic impurity on the local density of states in the iron-based superconductors,and obtained the relation between the intensities and positions of the impurity resonance peaks and the strength of the mixed impurity potential.Near the impurity point,the zero energy resonance peak is induced at a certain strength of the magnetic impurity,and the superconducting coherent peaks are suppressed.The zero energy peak splits with the variation of the magnetic impurity potential.It is also found that the curves of local density of states are basically same at the magnetic potentials Vm=|Vm| when thenonmagnetic potential Vs is fixed,and the resonance peaks at the positive and negative energy are symmetrical in a certain range of impurity potential.We also observe that the local density of states shows the features of the stronger magnetic or nonmagnetic impurity potential.In iron-based superconductors,different from non-magnetic impurities,magnetic impurities produce two(multiple)impurity resonance peaks,which are associated with spin up and spin down.With the increasing the strength of magnetic impurity,these peaks move periodically between the positive and negative energy sides.