Anisotropic Optical Properties of FePS₃

We have investigated the anisotropic dielectric functions of an antiferromagnetic semiconductor, FePS₃. Using a commercially available bulk sample, we performed Mueller matrix-based ellipsometry at multiple angles of incidence, and between 200 nm and 1700 nm. The isotropic model was used as a starting point to analyze each element of the Mueller matrix. In order to develop an anisotropic model, we also performed Mueller matrix-based ellipsometry measurements at several azimuthal angles. Initially, an isotropic model was developed for spectra obtained by conventional ellipsometry. Multiple measurements were performed to improve the signal, and the resulting spectra of each of the Mueller Matrix elements were modeled as a collection of oscillators associated with electronic transitions of FePS₃. This analysis shows that the dielectric functions of FePS₃ are biaxial, commensurate with its monoclinic crystal structure. The talk will also discuss how the dielectric functions change with temperature.