Temperature evolution of topological surface states in Bi_2Se_3 thin films studied using terahertz spectroscopy

摘要

We have measured the terahertz (THz) conductance of a 23 quintuple layer thick film of bismuth selenide (Bi_2Se_3) and found signatures for topological surface states (TSSs) below 50 K. We provide evidence for a topological phase transition as a function of lattice temperature by optical means. In this work, we used THz time-domain spectroscopy (THz-TDS) to measure the optical conductance of Bi_2Se_3, revealing metallic behavior at temperatures below 50 K. We measure the THz conductance of Bi_2Se_3 as 10 e~2/h at 4 K, indicative of a surface dominated response. Furthermore, the THz conductance spectra reveal characteristic features at ~1.9 THz attributed to the optical phonon mode, which is weakly visible at low temperatures but which becomes more prominent with increasing temperature. These results present a first look at the temperature-dependent behavior of TSSs in Bi_2Se_3 and the capability to selectively identify and address them using THz spectroscopy.