Single-crystal growth of iron-based superconductor La$_{0.34}$Na$_{0.66}$Fe$_2$As$_2$

TL;DR

This paper reports the successful growth of single crystals of La$_{0.34}$Na$_{0.66}$Fe$_2$As$_2$, revealing its magnetic and superconducting properties, and suggesting potential for further enhancement of its superconducting transition temperature.

Contribution

First successful growth of La$_{0.34}$Na$_{0.66}$Fe$_2$As$_2$ single crystals, providing new insights into its magnetic and superconducting behavior.

Findings

Superconducting transition temperature around 27 K.

Antiferromagnetic and structural transitions at 106 K.

Superconducting anisotropy approximately 1.9.

Abstract

We report single-crystal growth of La$_{0.34}$Na$_{0.66}$Fe$_2$As$_2$ iron-based superconductor with the size of several millimeters. The samples were accidentally obtained in trying to grow LaFeAsO$_{1-y}$F$_y$ ( $y \geq$ 0.8 ) single crystals with NaAs and NaF flux. The sample shows both antiferromagnetic and structural transitions at 106 K. The superconducting transition temperature is about 27 K with the superconducting anisotropy of about 1.9. These values and the temperature dependence of the Hall coefficient suggest that La$_{0.34}$Na$_{0.66}$Fe$_2$As$_2$ belongs to hole-doped "122" families of iron pnictides with the doping level slightly lower than optimal doping. Compared with previous reports on the polycrystalline samples, our results suggest that either $T_c$ of the this system can be further increased, or the superconducting dome may not be well formed in this system. In either case, the La$_{0.5-x}$Na$_{0.5+x}$Fe$_2$As$_2$ system provides a new platform to study the antiferromagnetic and superconducting properties of iron-based superconductors.