Surface-dominated conduction in a 6 nm thick Bi2Se3 thin film.

We report a direct observation of surface dominated conduction in an intrinsic Bi(2)Se(3) thin film with a thickness of six quintuple layers grown on lattice-matched CdS (0001) substrates by molecular beam epitaxy. Shubnikov-de Haas oscillations from the topological surface states suggest that the Fermi level falls inside the bulk band gap and is 53 ± 5 meV above the Dirac point, which is in agreement with 70 ± 20 meV obtained from scanning tunneling spectroscopies. Our results demonstrate a great potential of producing genuine topological insulator devices using Dirac Fermions of the surface states, when the film thickness is pushed to nanometer range.

Gate-controlled surface conduction in Na-doped Bi2Te3 topological insulator nanoplates.

Exploring exciting and exotic physics, scientists are pursuing practical device applications for topological insulators. The Dirac-like surface states in topological insulators are protected by the time-reversal symmetry, which naturally forbids backscattering events during the carrier transport process, and therefore offers promising applications in dissipationless spintronic devices. Although considerable efforts have been devoted to controlling their surface conduction, limited work has been focused on tuning surface states and bulk carriers in Bi(2)Te(3) nanostructures by external field. Here we report gate-tunable surface conduction in Na-doped Bi(2)Te(3) topological insulator nanoplates. Significantly, by applying external gate voltages, such topological insulators can be tuned from p-type to n-type. Our results render a promise in finding novel topological insulators with enhanced surface states.

Revelation of topological surface states in Bi2Se3 thin films by in situ Al passivation.

Topological insulators (TIs) are extraordinary materials that possess massless, Dirac-like topological surface states in which backscattering is prohibited due to the strong spin-orbit coupling. However, there have been reports on degradation of topological surface states in ambient conditions, which presents a great challenge for probing the original topological surface states after TI materials are prepared. Here, we show that in situ Al passivation inside a molecular beam epitaxy (MBE) chamber could inhibit the degradation process and reveal the pristine topological surface states. Dual evidence from Shubnikov-de Hass (SdH) oscillations and weak antilocalization (WAL) effect, originated from the π Berry phase, suggests that the helically spin-polarized surface states are well preserved by the proposed in situ Al passivation. In contrast, we show the degradation of surface states for the unpassivated control samples, in which the 2D carrier density is increased 39.2% due to ambient n-doping, the SdH oscillations are completely absent, and a large deviation from WAL is observed.