Query: Electric field effect in two‐dimensional transition metal dichalcogenides

Candidate papers:

abstract: Two dimensional (2D) materials have been an emerging platform for future device applications. Among them, 2D transition metal dichalcogenides (TMDs) have attracted substantial interest because of their fascinating properties ranging from semiconductor, semimetal, metal, to superconductor. The electric controllability over their physical properties is extremely important for their device application. This feature article presents recent progress in the electrical manipulation of the optical, electric, and spin/valley dependent properties of 2D TMDs. Also, some of the outstanding challenges and opportunities in this promising research field are highlighted.
author_names: Fucai Liu

Jiadong Zhou

Chao Zhu

Zheng Liu
title: Electric Field Effect in Two Dimensional Transition Metal Dichalcogenides
year: 2017

abstract: We studied the nonlinear electric response in WTe2 and MoTe2 monolayers. When the inversion symmetry is breaking but the the time reversal symmetry is preserved, a second order Hall effect called the nonlinear anomalous Hall effect (NLAHE) emerges owing to the nonzero Berry curvature on the nonequilibrium Fermi surface. We reveal a strong NLAHE with a Hall voltage that is quadratic with respect to the longitudinal current. The optimal current direction is normal to the mirror plane in these two dimensional (2D) materials. The NLAHE can be sensitively tuned by an out of plane electric field, which induces a transition from a topological insulator to a normal insulator. Crossing the critical transition point, the magnitude of the NLAHE increases, and its sign is reversed. Our work paves the way to discover exotic nonlinear phenomena in inversion symmetry breaking 2D materials.
author_names: Yang Zhang

Jeroen van den Brink

Claudia Felser

Binghai Yan
title: Electrically tuneable nonlinear anomalous Hall effect in two dimensional transition metal dichalcogenides WTe2 and MoTe2
year: 2018

abstract: Quantum spin Hall (QSH) effect materials feature edge states that are topologically protected from backscattering. However, the small band gap in materials that have been identified as QSH insulators limits applications. We use first principles calculations to predict a class of large gap QSH insulators in two dimensional transition metal dichalcogenides with 1T' structure, namely, 1T' MX2 with M (tungsten or molybdenum) and X (tellurium, selenium, or sulfur) A structural distortion causes an intrinsic band inversion between chalcogenide p and metal d bands. Additionally, spin orbit coupling opens a gap that is tunable by vertical electric field and strain. We propose a topological field effect transistor made of van der Waals heterostructures of 1T' MX2 and two dimensional dielectric layers that can be rapidly switched off by electric field through a topological phase transition instead of carrier depletion. First principles calculations are used to predict an exotic effect in a particular structure of WTe2 and related materials. Predicting an exotic state of matter Much like graphene, twodimensional flakes of transition metal dichalcogenides have appealing electronic properties. Qian et al. now find that certain structures of these materials may also exhibit the so called spin Hall effect. The spin Hall effect represents an exotic state of matter in which a 2D material conducts electricity along its edge in a way that drastically reduces dissipation. To show this, the researchers used first principle calculations and found that the materials also feature a large band gap, which reduces undesirable conduction through the bulk. Their proposed device could be switched on and off quickly using an electric field. Science, this issue p. 1344
author_names: Xiaofeng Qian

Junwei Liu

Liang Fu

Ju Li
title: Quantum spin Hall effect in two dimensional transition metal dichalcogenides
venue: Science
year: 2014

abstract: We report a new class of large gap quantum spin Hall insulators in two dimensional transition metal dichalcogenides, namely, MX$_2$ with M=(Mo, W) and X=(S, Se, and Te) whose topological electronic properties are highly tunable by external electric field. We propose a novel topological field effect transistor made of these atomic layer materials and their van der Waals heterostructures. Our device exhibits parametrically enhanced charge spin conductance through topologically protected transport channels, and can be rapidly switched off by electric field through topological phase transition instead of carrier depletion. Our work provides a practical material platform and device architecture for topological quantum electronics.
author_names: Xiaofeng Qian

Junwei Liu

Liang Fu

Ju Li
title: Quantum Spin Hall Effect and Topological Field Effect Transistor in Two Dimensional Transition Metal Dichalcogenides
year: 2014

abstract: The band gap of two dimensional (2D) semiconductors can be efficiently tuned by gate electric field, which is so called the Stark effect. We report that doping, which is essential in realistic devices, will substantially change the Stark effect of few layer transition metal dichalcogenides in unexpected ways. Particularly in bilayer structures, because of the competition between strong quantum confinement and intrinsic screening length, electron and hole dopings exhibit surprisingly different Stark effects: doped electrons actively screen the external field and result in a nonlinear Stark effect; however, doped holes do not effectively screen the external field, causing a linear Stark effect that is the same as that of undoped materials. Our further analysis shows that this unusual doping effect is not limited within transition metal dichalcogenides but general for 2D structures. Therefore, doping plays a much more crucial role in functional 2D devices and this unusual Stark effect also provides a new degree of freedom to tune band gaps and optical properties of 2D materials.
author_names: Xiaobo Lu

Li Yang
title: Stark Effect of Doped Two Dimensional Transition Metal Dichalcogenides
year: 2017

abstract: Transition metal dichalcogenides TX2 (T W, Mo; X S, Se, Te) are layered materials that are available in ultrathin forms such as mono bi and multilayers, which are commonly known as two dimensional materials. They have an intrinsic band gap in the range of some 500 meV to 2 eV, depending on the composition and number of layers, and giant intrinsic spin orbit splittings for odd layer numbers, and, in conjunction with their high chemical and mechanical stability, they qualify as candidate materials for two dimensional flexible electronics and spintronics. The electronic structure of each TX2 material is very sensitive to external factors, in particular towards electric and magnetic fields. A perpendicular electric field reduces the band gap, and for some structures semiconductor metal transitions could be possible. Moreover, the electric field triggers the spin orbit splitting for bilayers. A magnetic field applied normal to the layers causes the Hall effect, which in some cases may result in a quantum (spin) Hall effect and thus in magnetic switches. Finally, we discuss how valleytronics is possible in these materials by selective interaction of electrons in the different valleys using polarized light.
author_names: Agnieszka Beata Kuc

Thomas Heine
title: The electronic structure calculations of two dimensional transition metal dichalcogenides in the presence of external electric and magnetic fields.
venue: Chemical Society reviews
year: 2015

abstract: We show that it is possible to obtain one dimensional (1D) spin channels at the lateral heterojunction of 2D transition metal dichalcogenides by a current flow without the necessity of any external magnetic field. This originates from the native spin orbit coupling of 2D materials in conjunction with the electric field that develops due to conduction band offset at the junction. Nonetheless, we show that the underlying physics is very different from the well known spin Hall effect. We find that the degree of spin polarization could be as high as 0.1 <inline formula><tex math notation="LaTeX"/tex math>/inline formula> for conduction band transport and 0.75 <inline formula><tex math notation="LaTeX"/tex math>/inline formula> for valence band transport at room temperature in a lateral heterostructure of typical 2D semiconductors such as <inline formula> <tex math notation="LaTeX"\rm MoS}_2$/tex math>/inline formula><inline formula><tex math notation="LaTeX"\rm WSe}_2$/tex math>/inline formula> We also find that the spin polarization increases with longitudinal (transport) effective mass due to increased momentum of the flowing electrons. Such 1D spin channels might allow probing of spin dynamics in confined phase spaces in addition to potentially contributing to spintronics applications.
author_names: Varun Mishra

Sayeef S Salahuddin
title: One Dimensional Spin Channel in Two Dimensional Transition Metal Dichalcogenide Heterostructures
venue: IEEE Transactions on Nanotechnology
year: 2018

abstract: The emergence of two dimensional (2D) materials has attracted a great deal of attention due to their fascinating physical properties and potential applications for future nano electronic devices. Since the first isolation of graphene, a Dirac material, a large family of new functional 2D materials have been discovered and characterized, including insulating 2D boron nitride, semiconducting 2D transition metal dichalcogenides and black phosphorus, and superconducting 2D bismuth strontium calcium copper oxide, molybdenum disulphide and niobium selenide, etc. Here, we report the identification of ferromagnetic thin flakes of Cr2Ge2Te6 (CGT) with thickness down to a few nanometers, which provides a very important piece to the van der Waals structures consisting of various 2D materials. We further demonstrate the giant modulation of the channel resistance of 2D CGT devices via electric field effect. Our results illustrate the gate voltage tunability of 2D CGT and the potential of CGT, a ferromagnetic 2D material, as a new functional quantum material for applications in future nanoelectronics and spintronics.
author_names: Wenyu Xing

Yangyang Chen

Patrick Michael Odenthal

Xiao Zhang

Wei Yuan

Tang Su

Qi Song

Tianyu Wang

Jiangnan Zhong

Shuang Jia

X C Xie

Yan Li

Wei Han
title: Electric field effect in multilayer Cr 2 Ge 2 Te 6 a ferromagnetic 2D material
year: 2017

abstract: As two dimensional (2D) transition metal dichalcogenides electronic devices are scaled down to the sub micrometer regime, the active layers of these materials are exposed to high lateral electric fields, resulting in electrical breakdown. In this regard, understanding the intrinsic nature in layer stacked 2D semiconducting materials under high lateral electric fields is necessary for the reliable applications of their field effect transistors. Here, we explore the electrical breakdown phenomena originating from avalanche multiplication in MoS2 field effect transistors with different layer thicknesses and channel lengths. Modulating the band structure and bandgap energy in MoS2 allows the avalanche multiplication to be controlled by adjusting the number of stacking layers. This phenomenon could be observed in transition metal dichalcogenide semiconducting systems due to its quantum confinement effect on the band structure. The relationship between the critical electric field for avalanche breakdown and bandgap energy is well fitted to a power law curve in both monolayer and multilayer MoS2.
author_names: Jinsu Pak

Yeonsik Jang

Junghwan Byun

Kyungjun Cho

Taeyoung Kim

jae-Keun Kim

Barbara Yuri Choi

Jiwon Shin

Yongtaek Hong

Seungjun Chung

Takhee Lee
title: Two Dimensional Thickness Dependent Avalanche Breakdown Phenomena in MoS2 Field Effect Transistors under High Electric Fields.
venue: ACS nano
year: 2018

abstract: We study the quantum nonlinear Hall effect in two dimensional (2D) materials with time reversal symmetry. When only one mirror line exists, a transverse charge current occurs in the second order response to an external electric field, as a result of the Berry curvature dipole in momentum space. Candidate 2D materials to observe this effect are two dimensional transition metal dichalcogenides (TMDCs) First, we use an ab initio based tight binding approach to demonstrate that monolayer {T}_{d} structure TMDCs exhibit a finite Berry curvature dipole. In the $1H$ and $1{T}\ensuremath{ phase of TMDCs, we show the emergence of a finite Berry curvature dipole with the application of strain and an electrical displacement field, respectively.
author_names: Jhih-Shih You

Shiang Fang

Su-Yang Xu

Efthimios Kaxiras

Tony Low
title: Berry curvature dipole current in the transition metal dichalcogenides family
year: 2018