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

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.