Optimizing the Bi_(2-x)Sb_(x)Te_(3-y)Se_(y) solid solutions to approach   the intrinsic topological insulator regime
  To optimize the bulk-insulating behavior in the topological insulator materials having the tetradymite structure, we have synthesized and characterized single-crystal samples of Bi_(2-x)Sb_(x)Te_(3-y)Se_(y) (BSTS) solid solution at various compositions. We have elucidated that there are a series of "intrinsic" compositions where the acceptors and donors compensate each other and present a maximally bulk-insulating behavior. At such compositions, the resistivity can become as large as several Ohmcm at low temperature and one can infer the role of the surface-transport channel in the non-linear Hall effect. In particular, the composition of Bi1.5Sb0.5Te1.7Se1.3 achieves the lowest bulk carrier density and appears to be best suited for surface transport studies. 
Zhi Ren, A. A. Taskin, Satoshi Sasaki, Kouji Segawa, Yoichi Ando
cond-mat.mtrl-sci