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Title: Electronic phenomena in graphene based van der Waals heterostructures
Author: Thompson, Joshua
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2019
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In this thesis, we model the electronic and optical properties of stacked structures of two-dimensional materials involving graphene. In particular, we discuss how the interplay between the type and alignment of these stacked two-dimensional crystals affects the observed physical properties. Tuning the misalignment between two graphene layers leads to stark modification to the resulting electronic band structure. By employing electronic Raman scattering, we show that it is theoretically possible to accurately determine the twist angle in twisted bilayer graphene samples close to the magic-angle. We propose a new parameterisation for the interlayer coupling between twisted graphene layers, and demonstrate that twisted trilayer graphene is the simplest system in which the coupling in aligned and misaligned graphene bilayer can be probed. By comparison to experimental photoemission data, we demonstrate the validity and self-consistency of our model. We discuss the tunnelling current across two van der Waals tunnelling transistors. In the first, one or both of the electrodes are made of two crystals forminga moiré superlattice at their interface. We investigate structures containing either aligned graphene/hexagonal boron nitride heterostructure, twisted bilayer graphene or aligned graphene on α-In2Te2 and show negative differential resistance is possible in such transistors. In the second case we propose a tunnelling junction in an external magnetic field perpendicular to the layers, where the source and drain electrode are comprised of bilayer and monolayer graphene respectively. We show that, due to the effective difference in tunnelling barrier width for electrons on the two layers of bilayer graphene and the valley-dependent wave function distribution between these layers, the valley polarisation of the current can be electrically tuned. We demonstrate that strong valley polarisation can be obtained in the clean limit, where strong-momentum conserving tunnelling dominates, and in lower quality devices where this constraint is lifted.
Supervisor: Takashina, Kei ; Mucha-Kruczynski, Marcin Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available