Weak antilocalization in Bi$_{\mathrm{2-}}_{x}$In$_{x}$Te$_{\mathrm{3}}$ single crystals

Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$ has recently been identified as one of the most promising systems with which to realize a three-dimensional topological insulator. However, the bulk, stoichiometric Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$ single crystals often exhibit $p$-type metallic electrical conduction due to the Bi$_{\mathrm{Te}}$-type antisite defects, which overshadows the contribution of surface states. We have established that, upon group III (indium and/or thallium) doping, the Fermi level of Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$ can be lifted from the valence band into the band gap, and eventually shifted into the conduction band. Such doping progressively changes the electrical conduction of Bi$_{\mathrm{2-}}_{x}$A$_{x}$Te$_{\mathrm{3}}$ (A $=$ In, Tl, and $x \quad =$ 0 $-$ 0.30) single crystals from $p$-type to $n$-type. This is observed via measurements of both the Hall effect and the Seebeck coefficient performed in the (0001) basal plane in the temperature range of 2 $-$ 300 K. At low levels, the temperature dependent in-plane electrical resistivity maintains its metallic character as the density of holes decreases. Heavier doping content, $x \quad =$ 0.20 (0.10) for In (Tl), drives the electrical resistivity into a prominent non-metallic regime displaying the weak anti-localization type of magnetoresistance at the lowest temperatures for Bi$_{\mathrm{1.80}}$In$_{\mathrm{0.20}}$Te$_{\mathrm{3}}$. At the highest concentration, the samples revert back into the metallic state with electron dominated conduction. Thermal conductivity measurements of Bi$_{\mathrm{2-}}_{x}$A$_{x}$Te$_{\mathrm{3}}$ single crystals, as examined by the Debye-Callaway phonon conductivity model, reveal a generally stronger point defect scattering of phonons upon doping.