Effects of the topological phase transition and band inversion on ultrafast dynamics in topological crystalline insulators*

Topological crystalline insulators, characterized by a gapless metallic state on their high-symmetry surfaces that is protected by crystalline symmetry, are realized both theoretically and experimentally in the Pb$_{1-x}$Sn$_{x}$Te and Pb$_{1-x}$Sn$_{x}$Se compounds. In these materials, a topological phase transition and band inversion can be induced by doping, pressure or temperature. We use femtosecond optical pump-probe spectroscopy to study the evolution of the ultrafast dynamics as a function of both temperature and doping in the Pb$_{1-x}$Sn$_{x}$Te system. The influence of these parameters on the topological phase transition and band inversion, as well as on quasiparticle dynamics, will be discussed.