Electronic transport in twisted double bilayer graphene
department or school: Science, Faculty of
department or school: Physics and Astronomy, Department of
data provider: DSpace
degree campus: UBCV
creator: Vishnu Radhan, Aswin
issued: 2020-10-24T08:05:02Z
issued: 2020
related degree: Master of Science - MSc
degree grantor: University of British Columbia
description: Two dimensional (2D) van der Waals materials with a lattice mismatch or a relative twist angle, stacked atop each other forms a moiré superlattice. The electronic properties of such a system can be modified by controlling the relative twist angle between the layers, the most famous example being magic-angle twisted bilayer graphene. Since the observation of correlated insulator states and superconductivity in this flat band moiré system, investigations on other 2D moiré systems has gathered pace. Two Bernal stacked bilayer graphene sheets twisted relative to each other, i.e., twisted double bilayer graphene, gives the additional opportunity of tuning the electronic structure by a displacement electric field. This thesis presents the fabrication and electrical transport measurements of twisted double bilayer graphene devices. In order to compare the efficacy of various fabrication techniques, we fabricated the devices using two different modified dry transfer techniques: “tear-and-stack” and “cut-and-stack”. By calculating the twist angles from the electrical transport data, we find the “cut-and-stack” technique to give a better control of the twist angle of the fabricated devices. Subsequently, we studied the transport properties of a device with a twist angle of 1.39 degree, in order to replicate the electronic phase diagram of twisted double bilayer graphene devices. Tuning the displacement electric field and carrier density independently in a double gated geometry, we were able to observe correlated insulating states at quarter, half and three-quarter filling of the moiré band for a range of electric field values. The evolution of these insulating states in an in-plane magnetic field suggests spin/valley polarization. Additionally, the metallic states surrounding the correlated insulating state at half-filling displays a strong temperature dependence and nonlinear current-voltage characteristics, the nature of which remains ambiguous in our measurements.
aggregated CHO: https://circle.library.ubc.ca/rest/handle/2429/76356
note: Electronic transport in twisted doublebilayer graphenebyAswin Vishnu RadhanB. Tech., Mahatma Gandhi University, Kerala, India, 2011M.Tech., AcSIR, India, 2013A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF SCIENCEinThe Faculty of Graduate and Postdoctoral Studies(Physics)THE UNIVERSITY OF BRITISH COLUMBIA(Vancouver)October 2020c© Aswin Vishnu Radhan 2020The following individuals certify that they have read, and recommend tothe Faculty of Graduate and Postdoctoral Studies for acceptance, the thesisentitled:Electronic Transport in Twisted Double Bilayer Graphenesubmitted by Aswin Vishnu Radhan in partial fulfillment of the require-ments for the degree of Master of Science in Physics.Examining Committee:Joshua Alexander Folk, Associate Professor, Physics and Astronomy, UBCSupervisorZiliang Ye, Assistant Professor, Physics and Astronomy, UBCAdditional ExamineriiAbstractTwo dimensional (2D) van der Waals materials with a lattice mismatch ora relative twist angle, stacked atop each other forms a moire´ superlattice.The electronic properties of such a system can be modified by controllingthe relative twist angle between the layers, the most famous example beingmagic-angle twisted bilayer graphene. Since the observation of correlatedinsulator states and superconductivity in this flat band moire´ system, inves-tigations on other 2D moire´ systems has gathered pace. Two Bernal stackedbilayer graphene sheets twisted relative to each other, i.e., twisted doublebilayer graphene, gives the additional opportunity of tuning the electronicstructure by a displacement electric field. This thesis presents the fabricationand electrical transport measurements of twisted double bilayer graphene de-vices. In order to compare the efficacy of various fabrication techniques, wefabricated the devices using two different modified dry transfer techniques:“tear-and-stack” and “cut-and-stack”. By calculating the twist angles fromthe electrical transport data…
has type: Thesis/Dissertation
date issued: 2020-11
is shown at: 10.14288/1.0394812
language: eng
degree discipline: Physics
provider: Vancouver : University of British Columbia Library
publisher: University of British Columbia
rights: Attribution-NonCommercial-NoDerivatives 4.0 International
rights URI: http://creativecommons.org/licenses/by-nc-nd/4.0/
scholar level: Graduate
type: Text
identifier URI: http://hdl.handle.net/2429/76356