Highly tunable electron transport in epitaxial topological insulator (Bi$_{\mathrm{1-x}}$Sb$_{\mathrm{x}})_{\mathrm{2}}$Te$_{\mathrm{3}}$ thin films

Three dimensional topological insulators have emerged as a novel type of quantum materials that may lead to ground-breaking applications such as quantum computation and spintronic devices. These applications, however, often require an insulating bulk. A lot of progress has been made in suppressing the bulk conductivity. Here we report the growth of single crystalline (Bi$_{\mathrm{1-x}}$Sb$_{\mathrm{x}})_{\mathrm{2}}$Te$_{\mathrm{3}}$ films on SrTiO$_{\mathrm{3}}$(111) substrates by molecular beam epitaxy (MBE). A full range of Sb-Bi compositions have been studied in order to obtain the lowest possible bulk conductivity. For the samples with optimized Sb compositions (x $=$ 0.5$\pm$0.1), the carrier type can be tuned from n-type to p-type with the help of a back-gate. Linear magnetoresistance has been observed at gate voltages close to the maximum in the longitudinal resistance of a (Bi$_{\mathrm{1-x}}$Sb$_{\mathrm{x}})_{\mathrm{2}}$Te$_{\mathrm{3}}$ sample. These highly tunable (Bi$_{\mathrm{1-x}}$Sb$_{\mathrm{x}})_{\mathrm{2}}$Te$_{\mathrm{3}}$ thin films provide an excellent platform to explore the intrinsic transport properties of the three dimensional topological insulators.