Evolution of lattice, spin, and charge properties across the phase diagram of FeSe1-x Sx

Abstract

A Raman scattering study covering the entire substitution range of the FeSe1-xSx solid solution is presented. Data were taken as a function of sulfur concentration x for 0≤x≤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 B1g phonon mode vary continuously across the entire range of sulfur substitution. The A1g 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 A1g symmetry vary discontinuously. The magnetic excitation centered at approximately 500 cm-1 disappears above x=0.23 where the A1g 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.