Unique phase diagram with narrow superconducting dome in EuFe$_2$(As$_{1-x}$P$_x$)$_2$ due to Eu$^{2+}$ local magnetic moments

TL;DR

This study reveals a narrow superconducting dome in EuFe$_2$(As$_{1-x}$P$_x$)$_2$ influenced by Eu$^{2+}$ magnetic moments, with superconductivity suppressed by ferromagnetic ordering beyond a specific phosphorus concentration.

Contribution

It demonstrates how Eu$^{2+}$ magnetic moments and a Lifshitz transition constrain superconductivity in EuFe$_2$(As$_{1-x}$P$_x$)$_2$, mapping pressure to chemical doping.

Findings

Superconductivity exists only in a narrow doping range 0.18 ≤ x ≤ 0.23.

Ferromagnetic Eu ordering suppresses superconductivity beyond x=0.23.

A Lifshitz transition coincides with the change in Eu magnetic order.

Abstract

The interplay between superconductivity and Eu$ ^{2+}$ magnetic moments in EuFe$_2$(As$_{1-x}$P$_x$)$_2$ is studied by electrical resistivity measurements under hydrostatic pressure on $x=0.13$ and $x=0.18$ single crystals. We can map hydrostatic pressure to chemical pressure $x$ and show, that superconductivity is confined to a very narrow range $0.18\leq x \leq 0.23$ in the phase diagram, beyond which ferromagnetic (FM) Eu ordering suppresses superconductivity. The change from antiferro- to FM Eu ordering at the latter concentration coincides with a Lifshitz transition and the complete depression of iron magnetic order.