Theoretical Study On In-gap Bound States Induced By Interstitial Fe Impurities In Iron-based Superconductors

The discovery of iron-based high temperature superconductors in 2008 has motivated the investigation of high temperature superconductivity.Similar to copper oxide superconductors,iron-based superconductors also have a layered structure.But due to their unique iron-arsenic layer structure,iron-based superconductors have more complex energy band structure than copper oxide superconductors.Doping can lead to the variations of physical properties of iron-based superconductors.Based on the two-orbit four-band tight binding model,the Hamiltonian of the interstitial Fe impurity system is established.The Hamiltonian is diagonalized by using the Bogoliubov transformation.The expression of the local density of state(LDOS)is derived by employing the Green's function method.Finally,the numerical calculations on the LDOS and the result analysis are carried out.It is shown that the LDOS at the interstitial Fe impurity(IFI)and the nearest neighboring(NN)Fe of IFI has the strong resonance peaks inside energy gap,which locations and heights depend on the hopping parameter t and the pairing parameterI(35)between the IFI and the NN Fe sites.These in-gap bound states could be observed by scanning tunneling microscopy experiments.