Nanoscale Surface Element Identification and Dopant Homogeneity in the High-$T_c$ Superconductor Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$

TL;DR

This study employs scanning tunneling microscopy to analyze the surface structure and dopant distribution in Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$, revealing non-clustering Pr dopants and insights into the high-$T_c$ superconducting phase.

Contribution

It provides the first nanoscale mapping of dopant distribution and surface termination in Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$, challenging the idea that dopant inhomogeneity causes high-$T_c$ superconductivity.

Findings

Pr dopants do not cluster but repel each other.

Surface termination identified via work function mapping.

High-$T_c$ phase unlikely due to Pr inhomogeneity.

Abstract

We use scanning tunneling microscopy to determine the surface structure and dopant distribution in Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$, the highest-$T_c$ member of the 122 family of iron-based superconductors. We identify the cleaved surface termination by mapping the local tunneling barrier height, related to the work function. We image the individual Pr dopants responsible for superconductivity, and show that they do not cluster, but in fact repel each other at short length scales. We therefore suggest that the low volume fraction high-$T_c$ superconducting phase is unlikely to originate from Pr inhomogeneity.