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 origins 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, FeTe1−xSex, intercalated FeSe materials, and monolayer FeSe and FeTe1−xSex on SrTiO3. 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.
Highlights
Instead of the large Fermi surfaces seen in cuprates at optimal doping, Fe-based systems display small Fermi surface pockets centered at high symmetry points
Such an interorbital scattering process was found to lead to a d-wave ground state, which appears to disagree with the absence of nodes on the small Z-centered pocket observed by Angle-resolved photoemission spectroscopy (ARPES) [330]
It is clear that relatively strong electron correlation and spin-orbit coupling play important roles and distinguish these materials, at least in degree, from their pnictide counterparts
Summary
After a dozen years of research into iron-based superconductivity (FeSC), a good deal has been learned about the phenomenology and microscopic origins of this fascinating phenomenon that can be generally agreed upon. The new states engendered by these modifications are thought to be related to one another, and some have remarkably similar Fermi surface structures, notably lacking hole bands at the Fermi level. Why such systems, in violation of the central paradigm established apparently quite generally for Fe-pnictides, should have the highest critical temperatures of the FeSC family, is the central current question of iron-based superconductivity research. We discuss reports of topological superconductivity in these materials
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