A. A. Taskin

Large bulk resistivity and surface quantum oscillations in the topological insulator Bi2Te2Se

Topological insulators are predicted to present novel surface transport phenomena, but their experimental studies have been hindered by a metallic bulk conduction that overwhelms the surface transport. We show that a new topological insulator, Bi2Te2Se, presents a high resistivity exceeding 1 Ohm-cm and a variable-range hopping behavior, and yet presents Shubnikov-de Haas oscillations coming from the surface Dirac fermions. Furthermore, we have been able to clarify both the bulk and surface transport channels, establishing a comprehensive understanding of the transport in this material. Our results demonstrate that Bi2Te2Se is the best material to date for studying the surface quantum transport in a topological insulator.

Manifestation of topological protection in transport properties of epitaxial Bi2Se3 thin films.

The massless Dirac fermions residing on the surface of three-dimensional topological insulators are protected from backscattering and cannot be localized by disorder, but such protection can be lifted in ultrathin films when the three-dimensionality is lost. By measuring the Shubnikov-de Haas oscillations in a series of high-quality Bi2Se3 thin films, we revealed a systematic evolution of the surface conductance as a function of thickness and found a striking manifestation of the topological protection: The metallic surface transport abruptly diminishes below the critical thickness of ~6 nm, at which an energy gap opens in the surface state and the Dirac fermions become massive. At the same time, the weak antilocalization behavior is found to weaken in the gapped phase due to the loss of π Berry phase.

Observation of dirac holes and electrons in a topological insulator.

We show that in the new topological-insulator compound Bi(1.5)Sb(0.5)Te(1.7)Se(1.3) one can achieve a surfaced-dominated transport where the surface channel contributes up to 70% of the total conductance. Furthermore, it was found that in this material the transport properties sharply reflect the time dependence of the surface chemical potential, presenting a sign change in the Hall coefficient with time. We demonstrate that such an evolution makes us observe both Dirac holes and electrons on the surface, which allows us to reconstruct the surface band dispersion across the Dirac point.

Angular-dependent oscillations of the magnetoresistance in Bi 2 Se 3 due to the three-dimensional bulk Fermi surface

We observed pronounced angular-dependent magnetoresistance (MR) oscillations in a high-quality

Ising-like spin anisotropy and competing antiferromagnetic-ferromagnetic orders in GdBaCo2O5.5 single crystals.

{\text{Bi}}_{2}{\text{Se}}_{3}

Quantum oscillations in a topological insulator Bi 1 − x Sb x

single crystal with the carrier density of

Berry phase of nonideal Dirac fermions in topological insulators

5\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }{\text{cm}}^{\ensuremath{-}3}

Odd-parity pairing and topological superconductivity in a strongly spin-orbit coupled semiconductor.

, which is a topological insulator with residual bulk carriers. We show that the observed angular-dependent oscillations can be well simulated by using the parameters obtained from the Shubnikov-de Haas oscillations, which clarifies that the oscillations are essentially due to the bulk Fermi surface. By completely elucidating the bulk oscillations, this result paves the way for distinguishing the two-dimensional surface state in angular-dependent MR studies in

Fermi level tuning and a large activation gap achieved in the topological insulator Bi2Te2Se by Sn doping

{\text{Bi}}_{2}{\text{Se}}_{3}

Origin of the large thermoelectric power in oxygen-variable RbBaC7O5+x (R=Gd,Nd)

with much lower carrier density. Besides, the present result provides a compelling demonstration of how the Landau quantization of a closed three-dimensional Fermi surface can give rise to pronounced angular-dependent MR oscillations.