Hole doping of p-type thin topological insulators

Recent studies of intrinsically n-type topological insulator (TI) Bi$_{2}$Se$_{3}$ demonstrated that doping with Cu introduces electrons into this system, and that in the narrow range of doping Cu$_{x}$Bi$_{2}$Se$_{3}$ becomes a superconductor below Tc 5 K. It is presumed that Cu intercalates into Van der Waals gaps in the tetradymite structure of layered Bi$_{2}$Se$_{3}$, although this remains to be confirmed. We report on hole doping experiments on the naturally p-type Te-based TIs: thin films of Bi$_{2}$Te$_{3}$ and nanocrystalline plates of Sb$_{2}$Te$_{3}$. The samples were iodine doped either during the growth or by the exposure to iodine vapor. Transport measurements on films indicate a very unusual T$^{3}$ temperature dependence of longitudinal resistivity. It drops significantly below 30 K with decreasing temperature, although the drop appears arrested by a metal-insulator transition in the 300 mK range. Magnetization measurements on nanoplates indicate the development of large diamagnetic signal. These results will be discussed in comparison with the superconductivity obtained by Cu doping in Bi$_{2}$Se$_{3}$. * Supported in part by NSF-DMR-1122594.