Superconductivity in LaFeAs$_{1-x}$P$_{x}$O: effect of chemical pressures and bond covalency

TL;DR

This study demonstrates that phosphorus doping induces superconductivity in LaFeAsO, with enhanced critical fields, by modifying chemical pressures and bond covalency, revealing new insights into the material's superconducting mechanism.

Contribution

It provides the first evidence that isovalent P doping induces bulk superconductivity in LaFeAsO and explores the roles of chemical pressure and bond covalency in this process.

Findings

Superconductivity appears at ~10 K for x=0.25-0.3

Upper critical field estimated at 27 T

Structural changes correlate with superconductivity

Abstract

We report the realization of superconductivity by an isovalent doping with phosphorus in LaFeAsO. X-ray diffraction shows that, with the partial substitution of P for As, the Fe$_2$As$_2$ layers are squeezed while the La$_2$O$_2$ layers are stretched along the c-axis. Electrical resistance and magnetization measurements show emergence of bulk superconductivity at $\sim$10 K for the optimally-doped LaFeAs$_{1-x}$P$_{x}$O ($x=0.25\sim0.3$). The upper critical fields at zero temperature is estimated to be 27 T, much higher than that of the LaFePO superconductor. The occurrence of superconductivity is discussed in terms of chemical pressures and bond covalency.