# Magnetism and superconductivity in Fe$_{1+y}$Te$_{1-x}$Se$_x$

## TL;DR

This review discusses how neutron scattering has advanced understanding of magnetic, structural, and electronic properties in Fe$_{1+y}$Te$_{1-x}$Se$_x$ superconductors, highlighting phase diagrams, orbital physics, and local magnetic correlations.

## Contribution

It synthesizes key neutron scattering findings to elucidate the interplay of magnetism, structure, and superconductivity in iron chalcogenide superconductors.

## Key findings

- Doping-dependent structural transitions mapped to the anisotropic random field Ising model.
- Evidence of orbital-selective Mott physics in Fe chalcogenides.
- Neutron scattering reveals local magnetic correlations linked to nematicity and superconductivity.

## Abstract

Neutron scattering has played a significant role in characterizing magnetic and structural correlations in Fe$_{1+y}$Te$_{1-x}$Se$_x$ and their connections with superconductivity. Here we review several key aspects of the physics of iron chalcogenide superconductors where neutron studies played a key role. These topics include the phase diagram of Fe$_{1+y}$Te$_{1-x}$Se$_{x}$, where the doping-dependence of structural transitions can be understood from a mapping to the anisotropic random field Ising model. We then discuss orbital-selective Mott physics in the Fe chalcogenide series, where temperature-dependent magnetism in the parent material provided one of the earliest cases for orbital-selective correlation effects in a Hund's metal. Finally, we elaborate on the character of local magnetic correlations revealed by neutron scattering, its dependence on temperature and composition, and the connections to nematicity and superconductivity.