Ironing out the details of unconventional superconductivity

TL;DR

This paper reviews the complex phenomena of unconventional superconductivity in iron-based materials, highlighting their unique properties, experimental insights, and theoretical developments that challenge traditional understanding.

Contribution

It provides a comprehensive overview of the recent advances in understanding the mechanisms and properties of unconventional superconductivity in iron-based compounds.

Findings

Multiple atomic orbitals influence superconducting gap structures

Iron-based superconductors reveal new insights into metallic states and quantum criticality

Development of novel experimental and theoretical tools for quantum materials

Abstract

Superconductivity is a remarkably widespread phenomenon observed in most metals cooled down to very low temperatures. The ubiquity of such conventional superconductors, and the wide range of associated critical temperatures, is readily understood in terms of the celebrated Bardeen-Cooper-Schrieffer (BCS) theory. Occasionally, however, unconventional superconductors are found, such as the iron-based materials, which extend and defy this understanding in new and unexpected ways. In the case of the iron-based superconductors, this includes a new appreciation of the ways in which the presence of multiple atomic orbitals can manifest in unconventional superconductivity, giving rise to a rich landscape of gap structures that share the same dominant pairing mechanism. Besides superconductivity, these materials have also led to new insights into the unusual metallic state governed by the Hund's interaction, the control and mechanisms of electronic nematicity, the impact of magnetic fluctuations and quantum criticality, and the significance of topology in correlated states. Over the thirteen years since their discovery, they have proven to be an incredibly fruitful testing ground for the development of new experimental tools and theoretical approaches, both of which have extensively influenced the wider field of quantum materials.