Bulk-Insulating Bi$_{2}$Se$_{3}$ Thin Films and Decoupled Topological Surface States

By applying the simple criteria given by Mott and Ioffe-Regel it is easily seen that even the best TIs are not true insulators in the Mott sense, but at best are weakly-insulating bad metals. However, band-bending effects contribute significantly to the TI transport properties, and we show that utilization of this band-bending effect can lead to a Mott insulating bulk state in the thin regime. This is realized in transport experiments on compensation doped Bi$_{2}$Se$_{3}$ thin-films, where the bulk-insulating picture is supported by enhanced surface mobilities, Hall effect, Shubnikov de-Haas oscillations as well a clear signature of a thickness dependant decoupling of surface states by analyzing the weak anti-localization effect.