Temperature dependences of dielectric function and critical points of SnSe

The temperature-dependent dielectric functions of orthorhombic single-crystal SnSe were determined along the a-, b-, and c-axes over the full temperature range from 27 to 350 K using spectroscopic ellipsometry. Intrinsic dielectric functions for each orientation were extracted by multilayer optical modeling to remove the contribution of the surface roughness layer. The obtained spectra exhibit notable temperature-induced shifts and broadening of interband transition features. Second-derivative analysis using the standard analytic expression was performed. This analysis enabled the identification of more than ten critical point (CP) transitions for each crystallographic direction. The temperature dependence of the CP energies was systematically analyzed, providing a quantitative comparison of their anisotropic behavior along the three principal axes. These findings provide a complete, temperature-resolved set of dielectric functions and transition energies for SnSe, offering a quantitative reference for optical modeling and device-oriented applications.