On the Remarkable Superconductivity of FeSe and its Close Cousins

TL;DR

This review discusses the unique superconducting properties of FeSe and related materials, highlighting recent discoveries of unconventional gap structures, topological effects, and their implications for understanding high-temperature superconductivity.

Contribution

It provides a comprehensive overview of experimental and theoretical developments in FeSe superconductors, emphasizing new topological phenomena and unconventional pairing mechanisms.

Findings

Unusual superconducting gap structures identified in FeSe family

Evidence of nontrivial topological effects in FeSe-related materials

Potential for Majorana bound states in these systems

Abstract

Emergent electronic phenomena in iron-based superconductors have been at the forefront of condensed matter physics for more than a decade. Much has been learned about the origin and intertwined roles of ordered phases, including nematicity, magnetism, and superconductivity, in this fascinating class of materials. In recent years, focus has been centered on the peculiar and highly unusual properties of FeSe and its close cousins. This family of materials has attracted considerable attention due to the discovery of unexpected superconducting gap structures, a wide range of superconducting critical temperatures, and evidence for nontrivial band topology, including associated spin-helical surface states and vortex-induced Majorana bound states. Here, we review superconductivity in iron chalcogenide superconductors, including bulk FeSe, doped bulk FeSe, FeTe$_{1-x}$Se$_x$, intercalated FeSe materials, and monolayer FeSe and FeTe$_{1-x}$Se$_x$ on SrTiO$_3$. We focus on the superconducting properties, including a survey of the relevant experimental studies, and a discussion of the different proposed theoretical pairing scenarios. In the last part of the paper, we review the growing recent evidence for nontrivial topological effects in FeSe-related materials, focusing again on interesting implications for superconductivity.