Quantum interference effects in a 3D topological insulator with high-temperature bulk-insulating behavior

The Bi₂Se₃-family of 3D topological insulators (3DTI) exhibit insulating bulk states and surface states presenting a Dirac cone. At low temperatures, the conduction channels through the bulk of the material are fully gapped, making 3DTIs perfect systems to study the 2D transport behavior of Dirac fermions. Here, we report a 3DTI Bi_1.1Sb_0.9STe₂ with a reduced level of defects, and thus, high-temperature insulating behavior in its bulk states. The insulator-to-metal transition occurs at ∼250 K, below which the bulk contributions are negligible. Even at room temperature, the conductivity contribution from the bulk channel is less than 20%. Quantum transport properties of topological surface states are observed in the Bi_1.1Sb_0.9STe₂ nanoflake devices, e.g., high Hall mobility (∼1150 cm²/V s at 3 K), strong Shubnikov-de Haas oscillations with π Berry phase, weak antilocalization, and electron-electron interaction. Notably, additional oscillation patterns with quasi-periodicity-in-B and field-independent amplitude features are observed. The surface dominant transport behavior up to room temperature suggests that Bi_1.1Sb_0.9STe₂ is a room temperature topological insulator for electronic/spintronic applications.