Mobility spectrum analysis on three-dimensional topological insulator BiSbTeSe₂

We conducted mobility spectrum analysis on a high quality three dimensional topological insulator film of BiSbTeSe₂ to extract mobility μ and carrier density n. Top and bottom gates were applied to tune the carrier density on top and bottom surfaces independently. At 1.5 K, when the conduction is entirely dominated by the Dirac surface states, we always find two dominant conduction channels (top and bottom surfaces), with $μ=500–3000$ cm²/(V s) and n on the order of $1012 cm−2$⁠. However, at sufficiently high temperature (⁠$T=85$ K), when the bulk contributes, a third channel with maximum mobility $μ ∼$ 400 cm²/(V s) and n on the order of $1011–1013 cm−2$ opens. Our data show the feasibility of the method to analyze the different conduction channels in a topological insulator, being also promising for other similar material systems.