Evolution of lattice, spin, and charge properties across the phase diagram of FeSe1−xSx

A Raman scattering study covering the entire substitution range of the ${\mathrm{FeSe}}_{1\ensuremath{-}x}{\mathrm{S}}_{x}$ solid solution is presented. Data were taken as a function of sulfur concentration $x$ for $0\ensuremath{\le}x\ensuremath{\le}1$, of temperature and of scattering symmetry. All types of excitations including phonons, spins, and charges are analyzed in detail. It is observed that the energy and width of the 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 ${\mathrm{cm}}^{\ensuremath{-}1}$ 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 nematostructural transition and thus tracks the phase boundary.