Topological insulators represent a new state of matter with surface charge carriers having a massless Dirac dispersion and locked helical spin polarization. Many exciting experiments have been proposed by theory, yet, their execution have been hampered by the extrinsic conductivity associated with the unavoidable presence of defects in Bi2Te3 and Bi2Se3 bulk single crystals as well as impurities on their surfaces. Here we present the preparation of Bi2Te3 thin films that are insulating in the bulk and the in-situ four-point-probe measurement of the conductivity of the Dirac states on surfaces that are intrinsically clean. The total amount of charge carriers in the experiment is of order 10^12 per cm2 only and mobilities up to 4600 cm2/Vs have been observed. This is achieved by carrying out the preparation, structural characterization, angle-resolved and x-ray photoemission analysis, and the temperature dependent four-point probe conductivity measurement all in-situ under ultra-high-vacuum conditions. The unique experimental approach opens the way to prepare devices that can exploit the intrinsic topological properties of the Dirac surface states.
Work done in collaboration with Katharina Hoefer, Christoph Becker, Diana Rata, Jesse Swanson, and Peter Thalmeier