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

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.