Impact of Disorder on the Superconducting Phase Diagram in BaFe$_2$(As$_{1-x}$P$_x$)$_2$

TL;DR

This study investigates how disorder affects the phase diagram of BaFe$_2$(As$_{1-x}$P$_x$)$_2$, revealing that quantum-critical fluctuations play a key role in enhancing superconductivity by shifting the magnetic transition.

Contribution

It demonstrates how disorder via electron irradiation shifts the magnetic transition and influences the superconducting dome in an iron-based superconductor, highlighting the role of quantum-critical fluctuations.

Findings

Magneto-structural transition is suppressed with disorder.

Superconducting transition temperature $T_c$ initially increases with disorder at lower $x$.

Superconducting dome tracks the shift of the antiferromagnetic phase.

Abstract

In many classes of unconventional superconductors, the question of whether the superconductivity is enhanced by the quantum-critical fluctuations on the verge of an ordered phase remains elusive. One of the most direct ways of addressing this issue is to investigate how the superconducting dome traces a shift of the ordered phase. Here, we study how the phase diagram of the iron-based superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$ changes with disorder via electron irradiation, which keeps the carrier concentrations intact. With increasing disorder, we find that the magneto-structural transition is suppressed, indicating that the critical concentration is shifted to the lower side. Although the superconducting transition temperature $T_c$ is depressed at high concentrations ($x\gtrsim$0.28), it shows an initial increase at lower $x$. This implies that the superconducting dome tracks the shift of the antiferromagnetic phase, supporting the view of the crucial role played by quantum-critical fluctuations in enhancing superconductivity in this iron-based high-$T_c$ family.