Effect of surface morphology and magnetic impurities on the electronic structure in cobalt-doped BaFe2As2 superconductors

TL;DR

This study investigates how surface features and magnetic impurities affect the electronic structure of cobalt-doped BaFe2As2 superconductors, revealing that surface morphology does not influence the superconducting gap, but magnetic impurities do create in-gap states.

Contribution

It provides detailed surface characterization and clarifies the relationship between surface terminations, magnetic impurities, and electronic properties in Fe-based superconductors.

Findings

Superconducting gap widths are consistent across different surface morphologies.

Bright patches and dark stripes correspond to Ba and As surface terminations.

Magnetic impurities induce local in-gap states and suppress coherence peaks.

Abstract

Combined scanning tunneling microscopy, spectroscopy and local barrier height (LBH) studies show that low-temperature-cleaved optimally-doped Ba(Fe1-xCox)2As2 crystals with x=0.06, with Tc = 22 K, have complicated morphologies. Although the cleavage surface and hence the morphologies are variable, the superconducting gap maps show the same gap widths and nanometer size inhomogeneities irrelevant to the morphology. Based on the spectroscopy and LBH maps, the bright patches and dark stripes in the morphologies are identified as Ba and As dominated surface terminations, respectively. Magnetic impurities, possibly due to cobalt or Fe atoms, are believed to create local in-gap state and in addition suppress the superconducting coherence peaks. This study will clarify the confusion on the cleavage surface terminations of the Fe-based superconductors, and its relation with the electronic structures.