Optical-Pump Terahertz-Probe Spectroscopy of the Topological Crystalline Insulator Pb<sub>1–<i>x</i></sub>Sn<sub><i>x</i></sub>Se through the Topological Phase Transition
Zhenyang Xiao, Jiashu Wang, Xinyu Liu, Badih A. Assaf, David Burghoff
Abstract
Topological crystalline insulators, topological insulators whose properties are guaranteed by crystalline symmetry, can potentially provide a promising platform for terahertz optoelectronic devices, as their properties can be tuned on demand when layered in heterostructures. We perform the first optical-pump terahertz-probe spectroscopy of topological crystalline insulators, using them to study the dynamics of Pb1–xSnxSe as a function of temperature. At low temperatures, excitation of Dirac fermions leads to an increase in terahertz transmission; from this negative photoconductivity, the intrasubband relaxation rate of 6 ps is extracted. At high temperatures, where only massive Fermions exist, the free-carrier losses induced by the pump reduce the terahertz transmission for the duration of the 27 ps interband lifetime. Both effects are present at temperatures near the topological-to-trivial transition. Our experimental observations provide critical details for potential applications of Pb1–xSnxSe and provide a direct measurement of the topological character of Pb1–xSnxSe heterostructures.