Evolution of lattice, spin, and charge properties across the phase diagram of FeSe$_{1-x}$S$_x$

TL;DR

This Raman scattering study investigates how lattice, spin, and charge excitations evolve across the entire phase diagram of FeSe$_{1-x}$S$_x$, revealing continuous and discontinuous changes linked to phase transitions and excitations.

Contribution

It provides a comprehensive Raman analysis of FeSe$_{1-x}$S$_x$ across all sulfur concentrations, highlighting how excitations evolve with doping and temperature, and identifying phase boundary signatures.

Findings

Iron-related B$_{1g}$ phonon mode varies continuously with sulfur substitution.

A$_{1g}$ chalcogenide mode disappears above x=0.23 and reappears at higher energy.

Magnetic excitation at ~500 cm$^{-1}$ disappears above x=0.23, indicating a phase change.

Abstract

A Raman scattering study covering the entire substitution range of the FeSe$_{1-x}$S$_x$ solid solution is presented. Data were taken as a function of sulfur concentration $x$ for $0\le x \le 1$, of temperature and of scattering symmetry. All type of excitations including phonons, spins and charges are analyzed in detail. It is observed that the energy and width of iron-related B$_{1g}$ phonon mode vary continuously across the entire range of sulfur substitution. The A$_{1g}$ chalcogenide mode disappears above $x=0.23$ and reappears at a much higher energy for $x=0.69$. In a similar way the spectral features appearing at finite doping in A$_{1g}$ symmetry vary discontinuously. The magnetic excitation centered at approximately 500 cm$^{-1}$ disappears above $x=0.23$ where the A$_{1g}$ lattice excitations exhibit a discontinuous change in energy. The low-energy mode associated with fluctuations displays maximal intensity at the nemato-structural transition and thus tracks the phase boundary.