Surface adatom conductance filtering in scanning tunneling spectroscopy of Co-doped BaFe2As2 iron pnictide superconductors

TL;DR

This study combines ab initio theory and experiments to reveal how surface adatoms influence tunneling conductance in scanning tunneling spectroscopy of Co-doped BaFe2As2 superconductors, highlighting the importance of surface filtering effects.

Contribution

It demonstrates the significant role of surface adatom filtering in tunneling conductance measurements of iron pnictide superconductors, providing new insights into surface effects in STM/STS.

Findings

Adatom filtering dominates the tunneling process from near-EF Fe3d states.

Surface Ba-related pathways influence differential conductance features.

Experimental data show particle-hole asymmetry and energy-dependent contrast inversion.

Abstract

We establish in a combination of ab initio theory and experiments that the tunneling process in scanning tunneling microscopy/spectroscopy on the A-122 iron pnictide superconductors - in this case BaFe$_{2-x}$Co$_x$As$_2$ - involve a strong adatom filtering of the differential conductance from the near-EF Fe3d states, which in turn originates from the top-most sub-surface Fe layer of the crystal. The calculations show that the dominance of surface Ba-related tunneling pathways leaves fingerprints found in the experimental differential conductance data, including large particle-hole asymmetry and an energy-dependent contrast inversion.