Optical-Pump Terahertz-Probe Spectroscopy of the Topological Crystalline Insulator Pb1–x Sn x Se through the Topological Phase Transition

• Published in: ACS photonics Vol. 9; no. 3; pp. 765 - 771
• Main Authors: Xiao, Zhenyang, Wang, Jiashu, Liu, Xinyu, Assaf, Badih A, Burghoff, David
• Format: Journal Article
• Language: English
• Published: American Chemical Society 16-03-2022
• Subjects: Dirac fermions; dynamics; conductivity; optical-pump terahertz-probe spectroscopy; topological crystalline insulators
• ISSN: 2330-4022; 2330-4022
• DOI: 10.1021/acsphotonics.1c01717

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–x Sn x Se 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–x Sn x Se and provide a direct measurement of the topological character of Pb1–x Sn x Se heterostructures.