1209.3290 (Liang Wu et al.)

An abrupt change in transport dynamics across the topological phase
transition in the (Bi$_{1-x}$In$_x$)$_2$Se$_3$ system    [PDF]

Liang Wu, R. Valdés Aguilar, M. Brahlek, A. V. Stier, L. S. Bilbro, Y. Lubashevsky, N. Bansal, S. Oh, N. P. Armitage

We have utilized time-domain terahertz (THz) spectroscopy to investigate the low frequency optical conductivity in (Bi$_{1-x}$In$_x$)$_2$Se$_3$ through its topological phase transition from the pure ($x=0$) compound to the topologically trivial strongly insulating material ($x>0.25$). We find a number of large changes in the spectral properties with indium (In) substitution. The thickness independent Drude peak shows only minor broadening at low In substitutions. However, above $x\sim0.05$ we observe a sudden collapse in the transport lifetime. This substitution level closely coincides with a maximum in the mid-infrared (MIR) absorption coefficient which can be identified with the substitution level where the band gap closes, the band structure inverts, and hence the topological class changes. We therefore associate the collapse in the transport lifetime with the loss of topological protection of surface states as the system enters the topologically trivial phase. The role of finite size effects in this transition is also discussed.

View original: http://arxiv.org/abs/1209.3290