Broadband spectroscopic characterization of topological crystalline insulator Pb$_{0.77}$Sn$_{0.23}$Se

Topological crystalline insulators (TCI) are novel materials in which mirror symmetry protects the presence of spin polarized surface states. In this talk I will present the temperature dependent optical properties of Pb$_{0.77}$Sn$_{0.23}$Se, a compound with a temperature dependent trivial to nontrivial topological phase transition. Reflectance and ellipsometry data between 6 meV - 5.95 eV will be discussed in conjunction with optical conductivity and the frequency dependent scattering rate, revealing hints of the topological phase transition.