Coexistence of superconductivity and antiferromagnetism in Ca$_{0.74(1)}$La$_{0.26(1)}$(Fe$_{1-x}$Co$_{x}$)As$_{2}$ single crystals

TL;DR

This study investigates the coexistence of superconductivity and antiferromagnetism in Ca$_{0.74}$La$_{0.26}$Fe$_{1-x}$Co$_x$As$_2$ single crystals, revealing microscopic coexistence in the underdoped region and analyzing phase diagram differences with related compounds.

Contribution

It provides the first detailed phase diagram of Ca$_{0.74}$La$_{0.26}$Fe$_{1-x}$Co$_x$As$_2$ and demonstrates microscopic coexistence of phases, contrasting with related compounds.

Findings

Superconductivity up to 20 K observed with Co doping.

Microscopic coexistence of superconductivity and antiferromagnetism in underdoped region.

Differences in phase diagrams linked to FeAs interlayer coupling and spacer layer character.

Abstract

We report the transport, thermodynamic, $\mu$SR and neutron study of the Ca$_{0.74(1)}$La$_{0.26(1)}$(Fe$_{1-x}$Co$_{x}$)As$_{2}$ single crystals, mapping out the temperature-doping level phase diagram. Upon Co substitution on the Fe site, the structural/magnetic phase transitions in this 112 compound are suppressed and superconductivity up to 20 K occurs. Our measurements of the superconducting and magnetic volume fractions show that these two phases coexist microscopically in the underdoped region, in contrast to the related 10-3-8 Ca$_{10}$(Pt$_{3}$As$_{8}$)((Fe$_{1-x}$Pt$_x$)$_{2}$As$_{2}$)$_{5}$ compound, where coexistence is absent. Supported by model calculations, we discuss the differences in the phase diagrams of the 112 and 10-3-8 compounds in terms of the FeAs interlayer coupling, whose strength is affected by the character of the spacer layer, which is metallic in the 112 and insulating in the 10-3-8.