Quantum Oscillations in a topological insulator Bi$_2$SeTe$_2$ with large bulk resistivity

To date, transport experiments on Topological Insulators are seriously hampered by bulk conductance $G_b$ arising from impurity bands or band bending. Because of the large $G_b$, the surface currents carried by the massless Dirac surface states have been very difficult to resolve. We report measurements on the new topological insulator Bi$_2$SeTe$_2$ which has an unusually highly bulk resistivity $\rho$ (6 $\Omega$cm at 4 K, or 1,000 times higher than in Bi2Te3). Despite the large $\rho$, Shubnikov-de Haas (SdH) oscillations are clearly resolved in the Hall conductance up to 38 K, which implies a very high surface mobility. In a field $B$ of 14 T, Landau Levels (LLs) n = 4-9 are well resolved. We will describe the value of the Onsager phase $\gamma$ fixed by the index plot of the LLs.