Unexpected weak spatial variation of local density of sates induced by individual Co impurity atoms in Na(Fe{1-x}Cox)As as revealed by scanning tunneling spectroscopy

TL;DR

This study uses scanning tunneling spectroscopy to examine the local electronic effects of Co impurities in Na(Fe{1-x}Cox)As, revealing unexpectedly weak spatial variation in local density of states near the impurities.

Contribution

It provides the first detailed spatial mapping of impurity effects in Na(Fe{1-x}Cox)As, challenging existing models of impurity scattering in this material.

Findings

Negligible spatial variation of local density of states near Co impurities

Presence of in-gap states elevating zero-bias conductance

Results constrain theoretical models of impurity scattering

Abstract

We use spatially resolved scanning tunneling spectroscopy in Na(Fe{1-x}Cox)As to investigate the impurity effect induced by Co dopants. The Co impurities are successfully identified, and the spatial distributions of local density of state at different energies around these impurities are investigated. It is found that the spectrum shows negligible spatial variation at different positions near the Co impurity, although there is a continuum of the in-gap states which lifts the zero-bias conductance to a finite value. Our results put constraints on the S+- and S++ models and sharpen the debate on the role of scattering potentials induced by the Co dopants.