Nematicity, magnetism and superconductivity in FeSe

TLDR

FeSe is a prototypical iron‑based superconductor whose nematic, magnetic, and superconducting phases intertwine, with a tunable transition temperature ranging from 8 K in bulk to nearly 40 K under pressure or in intercalated and thin‑film forms, yet the link between its nematic order and magnetism remains unclear. This review surveys the nematic, magnetic, and superconducting properties of FeSe and their mutual influence. The authors examine bulk FeSe under varying pressure and chemical substitution, comparing experimental data with iron‑pnictide analogs and theoretical models. They find that FeSe’s behavior aligns with iron‑pnictide trends, and theoretical insights help explain the coupling among its nematic, magnetic, and superconducting phases.

Abstract

Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, Tc, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.