Gate-tuned quantum oscillations of topological surface states in β-Ag(2)Te

We report the strong experimental evidence of the existence of topological surface states with large electric field tunability and mobility in β-Ag(2)Te. Pronounced 2D Shubnikov-de Haas oscillations have been observed in β-Ag(2)Te nanoplates. A Berry phase is determined to be near π using the Landau level fan diagram for a relatively wide nanoplate while the largest electric field ambipolar effect in topological insulator so far (~2500%) is observed in a narrow nanoplate. The π Berry phase and the evolution of quantum oscillations with gate voltage (V(g)) in the nanoplates strongly indicate the presence of topological surface states in β-Ag(2)Te. Moreover, the mobility of the narrow Ag(2)Te nanoplate is about several thousand cm(2)s(−1)V(−1). Our results suggest that β-Ag(2)Te has the potential to become an important material in the investigation of topological insulators.