Optical studies of topological insulator Bi1:5 Sb0:5 Te1:8 Se1:2 using terahertz time-domain spectroscopy.

• Main Author: Tang, Chi Sin.
• Other Authors: Chia Ee Min, Elbert
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Science::Physics::Descriptive and experimental mechanics
• Online Access: http://hdl.handle.net/10356/49280
• Institution: Nanyang Technological University

Topological insulators are insulating materials with conducting surface states and insulating bulk states. Their surface states are topologically protected, meaning that unlike ordinary surface states, they cannot be destroyed by impurities and imperfections. This property is attributed to the presence of time-reversal symmetry and spin-orbit interaction, which occurs in heavy elements such as mercury and bismuth. Topological insulators are currently one of the main focuses of condensed matter research. Using Terahertz Time-Domain Spectroscopy (THz-TDS), we studied the optical properties of 3D topological insulator Bi_$1:5$Sb_$0:5$Te_$1:8$Se_$1:2$ (BSTS). Measurements have been carried out using a THz-TDS Spectrometer of spectral range 0.4-3.5 THz with temperatures between 5 K and 150 K. By tting the material conductance to the Drude-Lorentz Model, it allows us to understand the optical properties and charged carrier dynamics of the topological insulator. Thus, enabling us to characterize both the bulk and the surface states of the material. Results have shown temperature-dependence in the conductance (G), plasma frequencies (wp) and scattering rates (gamma). We attribute a signi ficant contribution of the surface states to the Drude conductance while the Lorentz conductance to the bulk insulating state. This gives a clearer understanding on how the surface charged carriers evolve with temperature.