STM/STS study of the local density of states in Cu doped Fe(Se,Te) superconductors

Abstract

The scanning tunnel microscopy/scanning tunnel spectroscopy (STM/STS) measurements of the local quasiparticle density of states (LDOS) in Cu x -Fe1.01-x Se0.4Te0.6 (x = 0.01-0.03) superconductors were carried out. Critical temperatures Tc decrease with increasing Cu-impurity doping level x. STM images show clear regular square arrangements of spots with the lattice spacing ~ 0.38 nm as well as the randomly distributed large spots, which are most possibly due to excess Fe atoms. While the STM image resembles that of non-doped Fe(Se,Te), the LDOS map shows various extra spot structures with bright (with higher magnitudes of dI/dV) and dark (with lower magnitudes of dI/dV) regions. With increasing x, the number of such spots grows proportionally, indicating that these spots most probably correspond to the dopant Cu atoms.