Superconductivity at 33 K in "111" single crystals at ambient pressure

TL;DR

This paper reports the discovery of superconductivity at 33 K in phosphorus-doped NaFeAs single crystals at ambient pressure, surpassing previous pressure-induced transition temperatures in similar materials.

Contribution

It demonstrates that phosphorus doping in NaFeAs induces higher superconducting transition temperatures than pressure or other isoelectronic substitutions, providing new insights into iron-based superconductivity.

Findings

NaFeAs with phosphorus doping shows Tc of 33 K at ambient pressure.

Cobalt doping results in Tc of 19 K.

Phosphorus doping yields higher Tc than pressure in similar systems.

Abstract

We have successfully grown single crystalline NaFeAs with cobalt or phosphor doping. Bulk superconductivity occurs in NaFe$_{0.95}$Co$_{0.05}$As at 19 K while much higher transition temperature is observed in NaFeAs$_{0.8}$P$_{0.2}$, in which the Tc of 33 K is even higher than the highest value realized by applying pressure in NaFeAs and all other isoelectronic element substituted samples. We discuss these behaviours by comparison with 122 and 1111 systems. We hope that our findings will help improve our understanding of iron-based superconductivity.