Experimental evidence of the nanoscaled topological metallic surface state of Bi2Te3 and Sb2Te3 films

There is a standing fundamental issue of topological insulators that their theoretically predicted nanoscaled metallic surface state (3-5 nm) has never been demonstrated substantially by experiments. We have designed an experiment to clarify this issue by measuring the surface-state and bulk-state resistances of topological insulators of Bi2Te3 and Sb2Te3 thin films. Interestingly, we found that the measured surface-state resistivity is lower than that of the bulk-state by 5 orders of magnitude, which indicated that the nanoscaled surface state (3-5 nm) is metallic. Further, the surface-state resistances decrease monotonically with the temperature decreasing from room temperature down to 5 K, which clearly showed that the metallic temperature dependence is consistent with the presence of the topologically protected Dirac surface state. Differently, the bulk-state resistances firstly decrease, and then reach a rock bottom near 125 K, and then increase with decreasing temperature and achieve the saturated state near 50 K. These results definitely showed that the bulk state exhibits a typical temperature dependence of insulators. Our experiments have, for the first time, provided the experimental evidence of the theoretically predicted nanoscaled metallic surface state of topological insulators. Copyright (C) EPLA, 2011