Competing magnetic double-Q phases and superconductivity-induced re-entrance of C2 magnetic stripe order in iron pnictides

TL;DR

This paper presents a microscopic theoretical analysis of magnetic phases in iron pnictides, revealing how competing magnetic orders and superconductivity influence phase stability and lead to re-entrant magnetic stripe order, aligning with experimental observations.

Contribution

It introduces a detailed theoretical framework for understanding competing magnetic phases and their interaction with superconductivity in iron pnictides, including disorder effects.

Findings

Double-Q phases exist at the foot of the magnetic dome.

Superconductivity suppresses double-Q phases more strongly.

Re-entrance of single-Q magnetic order occurs due to superconductivity.

Abstract

We perform a microscopic theoretical study of the generic properties of competing magnetic phases in iron pnictides. As a function of electron filling and temperature, the magnetic stripe (single-Q) order forms a dome, but competing non-collinear and non-uniform double-Q phases exist at the foot of the dome in agreement with recent experiments. We compute and compare the electronic properties of the different magnetic phases, investigate the role of competing superconductivity, and show how disorder may stabilize double-Q order. Superconductivity is shown to compete more strongly with double-Q magnetic phases, which can lead to re-entrance of the C2 (single-Q) order in agreement with recent thermal expansion measurements on K-doped Ba-122 crystals.