Observation of huge surface hole mobility in the topological insulator Bi(0.91)Sb(0.09) (111)

We report the first direct measurement of transport properties of surface states in the topological insulator Bi(0.91)Sb(0.09) (111) from the weak-field Hall effect and Shubnikov-de Haas oscillations. We find that the holelike surface band displays an unexpectedly high mobility 23,000-85,000 cm(2)/V s, which is the highest mobility so far reported in bismuth-based topological insulators. This result provides the first quantitative assessment of the effect of alloy disorder on the mobility of surface states in topological insulators. We show that the 9% alloy disorder decreases the mobility of surface states by a factor of less than 2.3.