Doping-Enhanced Antiferromagnetism in Ca1-xLaxFeAs2

TL;DR

This study reveals that in Ca$_{1-x}$La$_x$FeAs$_2$, antiferromagnetism is unexpectedly strengthened by doping, coexisting with superconductivity, challenging the typical suppression of antiferromagnetism in iron-based superconductors.

Contribution

The paper demonstrates that doping in Ca$_{1-x}$La$_x$FeAs$_2$ enhances antiferromagnetic order, providing new insights into the phase diagram of iron-based high-$T_c$ superconductors.

Findings

Antiferromagnetic order occurs below 62 K at x=0.15.

$T_N$ increases to 70 K at x=0.24.

Superconductivity appears at 35 K coexisting with antiferromagnetism.

Abstract

In iron pnictides, high temperature superconductivity emerges after suppressing antiferromagnetism by doping. Here we show that antiferromagnetism in Ca$_{1-x}$La$_x$FeAs$_2$ is robust against and even enhanced by doping. Using $^{75}$As-nuclear magnetic resonance and nuclear quadrupole resonance techniques, we find that an antiferromagnetic order occurs below the N\'eel temperature $T_{\rm N}$ = 62 K at a high doping concentration ($x$ = 0.15) where superconductivity sets in at the transition temperature $T_{\rm c}$ = 35 K. Unexpectedly, $T_{\rm N}$ is enhanced with increasing doping, rising up to $T_{\rm N}$ = 70 K at $x$ = 0.24. The obtained phase diagram of this new system enriches the physics of iron-based high-$T_{\rm c}$ superconductors.