Conductance modulation in topological insulator Bi2Se3 thin films with
  ionic liquid gating

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Abstract

A Bi2Se3 topological insulator field effect transistor is investigated by using ionic liquid as an electric double layer gating material, leading to a conductance modulation of 365% at room temperature. We discuss the role of charged impurities on the transport properties. The conductance modulation with gate bias is due to a change in the carrier concentration, whereas the temperature dependent conductance change is originated from a change in mobility. Large conductance modulation at room temperature along with the transparent optical properties makes topological insulators as an interesting (opto)electronic material.

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A topological Dirac insulator in a quantum spin Hall phase : Experimental observation of first strong topological insulator

R. Cava, D Hsieh, M. Hasan … (2009)

When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the extreme quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic field. Bulk Bi\(_{1-x}\)Sb\(_x\) single crystals are expected to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher dimensional analogues of the edge states that characterize a spin Hall insulator. In addition to its interesting boundary states, the bulk of Bi\(_{1-x}\)Sb\(_x\) is predicted to exhibit three-dimensional Dirac particles, another topic of heightened current interest. Here, using incident-photon-energy-modulated (IPEM-ARPES), we report the first direct observation of massive Dirac particles in the bulk of Bi\(_{0.9}\)Sb\(_{0.1}\), locate the Kramers' points at the sample's boundary and provide a comprehensive mapping of the topological Dirac insulator's gapless surface modes. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the much sought exotic "topological metal". They also suggest that this material has potential application in developing next-generation quantum computing devices.

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Quantum oscillations and hall anomaly of surface states in the topological insulator Bi2Te3.

Dong-Xia Qu, Y. Hor, Jun Xiong … (2010)

Topological insulators are insulating materials that display massless, Dirac-like surface states in which the electrons have only one spin degree of freedom on each surface. These states have been imaged by photoemission, but little information on their transport parameters, for example, mobility, is available. We report the observation of Shubnikov-de Haas oscillations arising from the surface states in nonmetallic crystals of Bi(2)Te(3). In addition, we uncovered a Hall anomaly in weak fields, which enables the surface current to be seen directly. Both experiments yield a surface mobility (9000 to 10,000 centimeter(2) per volt-second) that is substantially higher than in the bulk. The Fermi velocity of 4 x 10(5) meters per second obtained from these transport experiments agrees with angle-resolved photoemission experiments.

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Mobility engineering and metal-insulator transition in monolayer MoS2

, (2013)

Two-dimensional (2D) materials are a new class of materials with interesting physical properties and ranging from nanoelectronics to sensing and photonics. In addition to graphene, the most studied 2D material, monolayers of other layered materials such as semiconducting dichalcogenides MoS2 or WSe2 are gaining in importance as promising insulators and channel materials for field-effect transistors (FETs). The presence of a direct band gap in monolayer MoS2 due to quantum mechanical confinement, allows room-temperature field-effect transistors with an on/off ratio exceeding 108. The presence of high-k dielectrics in these devices enhanced their mobility, but the mechanisms are not well understood. Here, we report on electrical transport measurements on MoS2 FETs in different dielectric configurations. Mobility dependence on temperature shows clear evidence of the strong suppression of charge impurity scattering in dual-gate devices with a top-gate dielectric together with phonon scattering that shows a weaker than expected temperature dependence. High levels of doping achieved in dual-gate devices also allow the observation of a metal-insulator transition in monolayer MoS2. Our work opens up the way to further improvements in 2D semiconductor performance and introduces MoS2 as an interesting system for studying correlation effects in mesoscopic systems.