Probing Local Variations of Superconductivity on the Surface of Ba(Fe1-xCox)2As2 Single Crystals

TL;DR

This study uses scanning tunneling microscopy to investigate local variations in superconductivity on Ba(Fe1-xCox)2As2 surfaces, revealing that compositional differences influence superconducting transition temperatures.

Contribution

It provides detailed spatially resolved analysis linking local compositional changes to variations in superconducting properties.

Findings

Superconducting transition temperature (TC) varies locally from 19.6 to 22.2 K.

Uniform regions show consistent TC and Co concentration.

Non-uniform regions exhibit correlated compositional and superconducting variations.

Abstract

The spatially resolved electrical transport properties have been studied on the surface of optimally-doped superconducting Ba(Fe1-xCox)2As2 single crystal by using a four-probe scanning tunneling microscopy. While some non-uniform contrast appears near the edge of the cleaved crystal, the scanning electron microscopy (SEM) reveals mostly uniform contrast. For the regions that showed uniform SEM contrast, a sharp superconducting transition at TC = 22.1 K has been observed with a transition width (delta)Tc = 0.2 K. In the non-uniform contrast region, TC is found to vary between 19.6 and 22.2 K with (delta)Tc from 0.3 to 3.2 K. The wavelength dispersive x-ray spectroscopy reveals that Co concentration remains 7.72% in the uniform region, but changes between 7.38% and 7.62% in the non-uniform region. Thus the variations of superconductivity are associated with local compositional change.