Search query: Visualizing electrostatic gating effects in two-dimensional heterostructures

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abstract: The ability to directly monitor the states of electrons in modern field effect devices for example, imaging local changes in the electrical potential, Fermi level and band structure as a gate voltage is applied could transform our understanding of the physics and function of a device. Here we show that micrometre scale, angle resolved photoemission spectroscopy1 3 (microARPES) applied to two dimensional van der Waals heterostructures4 affords this ability. In two terminal graphene devices, we observe a shift of the Fermi level across the Dirac point, with no detectable change in the dispersion, as a gate voltage is applied. In two dimensional semiconductor devices, we see the conduction band edge appear as electrons accumulate, thereby firmly establishing the energy and momentum of the edge. In the case of monolayer tungsten diselenide, we observe that the bandgap is renormalized downwards by several hundreds of millielectronvolts approaching the exciton energy as the electrostatic doping increases. Both optical spectroscopy and microARPES can be carried out on a single device, allowing definitive studies of the relationship between gate controlled electronic and optical properties. The technique provides a powerful way to study not only fundamental semiconductor physics, but also intriguing phenomena such as topological transitions5 and many body spectral reconstructions under electrical control.Changes in the electronic states of two dimensional semiconductor devices resulting from electrical gating can be monitored directly using micrometre scale angle resolved photoemission spectroscopy.
author_names: Paul V Nguyen

Natalie C Teutsch

N P Wilson

Joshua Kahn

Xue Xia

Abigail J Graham

Viktor Kandyba

Alessio Giampietri

Alexei Barinov

Gabriela Constantinescu

Nelson C Y Yeung

N Hine

Xiaodong Xu

David H Cobden

Neil R Wilson
title: Visualizing electrostatic gating effects in two dimensional heterostructures
venue: Nature
year: 2019

abstract: Electrostatic gating enables key functionality in modern electronic devices by altering the properties of materials. While classical electrostatics is usually sufficient to understand the effects of gating in extended systems, the inherent quantum properties of gating in nanostructures offer unexplored opportunities for materials and devices. Using first principles calculations for Co/bilayer graphene, Co/BN/graphene, and Co/BN/benzene, as well as a simple physical model, we show that heterostructures with two dimensional materials yield tunable magnetic proximity effects. van der Waals bonding is identified as a requirement for large electronic structure changes by gating, enabling both the magnitude and sign change of spin polarization in physisorbed graphene. The ability to electrically reverse the spin polarization of an electrode provides an alternative to using the applied magnetic field or spin transfer torque in spintronic devices, thus transforming a spin valve into a spin transistor.
author_names: Predrag Lazic

K D Belashchenko

Igor Zutic
title: Effective gating and tunable magnetic proximity effects in two dimensional heterostructures
year: 2016

abstract: Up to almost the last two decades all the experimental results concerning the quantum Hall effect (QHE) i.e. the observation of plateaux at integer (IQHE) or fractional (FQHE) values of the constant h/e2, were related to quantum wells in semiconductor heterostructures (QWs) However, more recently, a renewed interest in revisiting these phenomena has arisen thanks to the observation of entirely similar effects in graphene and topological insulators. In this paper we show an approach encompassing all these QHEs using the same theoretical frame, entailing both Hall effect plateaux and Shubnikov de Haas (SdH) oscillations. Moreover, the model also enables the analysis of both phenomena as a function not only of the magnetic field but the gate voltage as well. More specifically, in light of the approach, the FQHE in any two dimensional electron system (2DES) appears to be an effect of the breaking of the degeneration of every Landau level, n, as a result of the electrostatic interaction involved, and being characterized by the set of three integer numbers (n, p, q) where p and q have clear physical meanings too.
author_names: Miguel A Hidalgo
title: Quantum Hall effects in two dimensional electron systems: A global approach
year: 2020

abstract: Magnetic monopoles have been proposed as emergent quasiparticles in pyrochlore spin ice compounds. However, unlike semiconductors and two dimensional electron gases where the charge degree of freedom can be actively controlled by chemical doping, interface modulation, and electrostatic gating, there is as of yet no analogue of these effects for emergent magnetic monopoles. To date, all experimental investigations have been limited to large ensembles comprised of equal numbers of monopoles and antimonopoles in bulk crystals. To address these issues, we propose the formation of a two dimensional magnetic monopole gas (2DMG) with a net magnetic charge, confined at the interface between a spin ice and an isostructural antiferromagnetic pyrochlore iridate and whose monopole density can be controlled by an external field. Our proposal is based on Monte Carlo simulations of the thermodynamic and transport properties. This proposed 2DMG should enable experiments and devices which can be performed on magnetic monopoles, akin to two dimensional electron gases in semiconductor heterostructures. Heterostructure interfaces have physical properties distinct from bulk materials, providing the basis for many electronic devices. Miao et al. propose a spin ice heterostructure that can host a two dimensional gas of emergent magnetic monopoles with a net magnetic charge.
author_names: Ludi Miao

Y Lee

Antonio B Mei

Michael J Lawler

Kyle M Shen
title: Two dimensional magnetic monopole gas in an oxide heterostructure
venue: Nature Communications
year: 2020

abstract: We systematically explore the electronic and transport properties of Graphene CrBr$_{3} heterolayer based on \emph{ab initio} density functional theory simulations. Our result shows the modulation in electronic band gap with applied electric field variation from 0.5 to +0.5 V/\AA} The electric field variation marked linear and non linear trend for band gap modulation due to polarization effects between the two layers. It is found that the transmission at the interface is spin polarized upto 71.2\ and the magnetic moment is found to be invariant. Moreover, complex band structure and transmission spectrum reveals the possibilities of spin transmission in Graphene CrBr$_{3} heterostructure via magnetic proximity effect. The merits of electric field tunability and magnetic proximity effect in this 2D layered ferromagnetic semiconductor heterostructure will be beneficial to extend its suitability in spintronics device applications.
author_names: Sushant Kumar Behera

Mayuri Bora

Sapta Sindhu Paul Chowdhury

Pritam Deb
title: Magnetic proximity effect and electric field modulation in Graphene CrBr$_{3} van der Waals heterostructure
year: 2019

abstract: In a fast developing field, it has been found that van der Waals heterostructures can overcome the weakness of single two dimensional layered materials and extend their electronic and optoelectronic applications. Through first principles methods, the studied MoS2/stanene heterostructure preserves high speed carrier characteristics and opens the direct band gap. Simultaneously, the band alignment shows that the electrons transfer from stanene to MoS2, which forms an internal electric field. As an effective strategy, the out of plane strain remarkably changes the band gaps of the heterostructure and enhances its carrier concentration. In addition, the combined effects of the internal and external electric fields can further open the band gaps and induce a direct to indirect gap transition in the heterostructure. More interestingly, when the external electric field is equal to the reverse internal one, the heterostructure regains a Dirac cone. Our results show that the MoS2/stanene heterostructure has potential applications in high speed optoelectronic devices.
author_names: Wenqi Xiong

Congxin Xia

Juan Du

Tianxing Wang

Yuting Peng

Zhongming Wei

Jingbo Li
title: Band engineering of the MoS2/stanene heterostructure: strain and electrostatic gating.
venue: Nanotechnology
year: 2017

abstract: Electrons in an artificially created periodic potential a superlattice follow Bloch's theorem, and they reside in minibands. This approach is particularly suitable to study effects inaccessible in natural crystals, such as Hofstadter's butterfly. After pioneering experiments using high mobility GaAs based superlattices, additional proof came with graphene hexagonal boron nitride (hBN) heterostructures forming moire superlattices. However, both lattice symmetry and period are constrained by the crystal lattices of graphene and hBN, and the exact potential is governed by, e.g. strain or local band gaps, which are virtually impossible to be controlled experimentally. A first approach to circumvent this was recently presented by Forsythe et al. who employed a patterned dielectric, and demonstrated gate tunable superlattice effects. In this work, combining patterned and uniform gates, we demonstrate satellite resistance peaks corresponding to Dirac cones to fourth order, and the Hofstadter butterfly, including the non monotonic quantum Hall response predicted by Thouless et al. The exact potential shape can be determined from elementary electrostatics, allowing for a detailed comparison between miniband structure and calculated transport characteristics. We thus present a comprehensive picture of graphene based superlattices, featuring a broad range of miniband effects, both in experiment and in our theoretical modeling.
author_names: R Huber

Ming-Hao Liu

Sz-Chao Chen

Martin Drienovsky

Andreas Sandner

Kenji Watanabe

Takashi Taniguchi

Klaus Richter

Dieter Weiss

Jonathan Eroms
title: Tunable two dimensional superlattices in graphene
year: 2020

abstract: Electrostatic gating is pervasive in materials science, yet its effects on the electronic band structure of materials has never been revealed directly by angle resolved photoemission spectroscopy (ARPES) the technique of choice to noninvasively probe the electronic band structure of a material. By means of a state of the art ARPES setup with submicron spatial resolution, we have investigated a heterostructure composed of Bernal stacked bilayer graphene (BLG) on hexagonal boron nitride and deposited on a graphite flake. By voltage biasing the latter, the electric field effect is directly visualized on the valence band as well as on the carbon 1s core level of BLG. The band gap opening of BLG submitted to a transverse electric field is discussed and the importance of intra layer screening is put forward. Our results pave the way for new studies that will use momentum resolved electronic structure information to gain insight on the physics of materials submitted to the electric field effect.
author_names: Frederic Joucken

Jos'e Avila

Zhehao Ge

Eberth A Quezada-Lopez

Hemian Yi

Romaric Le Goff

Emmanuel Baudin

John L Davenport

Kenji Watanabe

Takashi Taniguchi

Maria Carmen Asensio

Jairo Velasco
title: Visualizing the Effect of an Electrostatic Gate with Angle Resolved Photoemission Spectroscopy.
venue: Nano letters
year: 2019

abstract: We study the effects of electrostatic gating on the lateral distribution of charge carriers in two dimensional devices, in a non linear dielectric environment. We compute the charge distribution using the Thomas Fermi approximation to model the electrostatics of the system. The electric field lines generated by the gate are focused at the edges of the device, causing an increased depletion near the edges, compared to the center of the device. This effect strongly depends on the dimensions of the device, and the non linear dielectric constant of the substrate. We experimentally demonstrate this effect using scanning superconducting interference device (SQUID) microscopy images of current distributions in gated LaAlO$_3$/SrTiO$_3$ heterostructures.
author_names: Eylon Persky

Hyeok Yoon

Yanwu Xie

Harold Y Hwang

Jonathan Ruhman

Beena Kalisky
title: Electrostatic modulation of the lateral carrier density profile in field effect devices with non linear dielectrics
year: 2020

abstract: Here, we have investigated size dependent electron mobility in an electrostatically evolved AlGaN/GaN one dimensional channel from a two dimensional heterostructure. An architecture with lateral gates, which allows partial depletion of channel widths, has been used. The low field mobility is found to manifest multiple peaks and valleys for progressively changing quantum confinement. The number of sub bands increases with the increasing dimension. However, electron and phonon confinement decrease, which leads to less wave function overlap. Although an increase in the number of sub bands decreases the mobility due to the larger number of density of states, the overlap decreases monotonically which increases the mobility. The two competing effects lead to a unique signature on the mobility. The depletion region voltage exponent is found to differ from the traditional value of 0.5 in this case. The exponent is found to be close to unity for a one dimensional system.Here, we have investigated size dependent electron mobility in an electrostatically evolved AlGaN/GaN one dimensional channel from a two dimensional heterostructure. An architecture with lateral gates, which allows partial depletion of channel widths, has been used. The low field mobility is found to manifest multiple peaks and valleys for progressively changing quantum confinement. The number of sub bands increases with the increasing dimension. However, electron and phonon confinement decrease, which leads to less wave function overlap. Although an increase in the number of sub bands decreases the mobility due to the larger number of density of states, the overlap decreases monotonically which increases the mobility. The two competing effects lead to a unique signature on the mobility. The depletion region voltage exponent is found to differ from the traditional value of 0.5 in this case. The exponent is found to be close to unity for a one dimensional system.
author_names: Akhil S Kumar

Navya S Garigapati

D Saha
title: Low field mobility in electrostatically evolved AlGaN/GaN one dimensional channel from a two dimensional electron gas system
venue: Applied Physics Letters
year: 2019