Evolution of the Phase Diagram of LaFeP$_{1-x}$As$_{x}$O$_{1-y}$F$_{y}$ ($y$ = 0 -- 0.1)

TL;DR

This study investigates how phosphorus/arsenic substitution and fluorine doping influence the superconducting and magnetic phase diagram of LaFeP$_{1-x}$As$_{x}$O$_{1-y}$F$_{y}$, revealing the evolution of two distinct superconducting domes.

Contribution

It demonstrates the emergence and merging of two superconducting domes with varying F content, indicating different Fermi surface states in the material.

Findings

A new superconducting dome appears around x=0--0.3 with T_c up to 12 K.

Two separate superconducting domes are observed at y=0, separated by an antiferromagnetic region.

Increasing fluorine content merges the domes into a single peak, indicating different Fermi surface states.

Abstract

P/As-substitution effects on the transport properties of polycrystalline LaFeP$_{1-x}$As$_{x}$O$_{1-y}$F$_{y}$ with $x$ = 0 -- 1.0 and $y$ = 0 -- 0.1 have been studied. In the F-free samples ($y$ = 0), a new superconducting (SC) dome with a maximum $T_{c}$ of 12 K is observed around $x$ = 0 -- 0.3. This is separated from another SC dome with $T_{c}$ $\sim$10 K at $x$ = 0.6 -- 0.8 by an antiferromagnetic region ($x$ = 0.3 -- 0.6), giving a two-dome feature in the $T_{c}-x$ phase diagram. As $y$ increases, the two SC domes merge together, changing to a double peak structure at $y$ = 0.05 and a single dome at $y$ = 0.1. This proves the presence of two different Fermi surface states in this system.