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Title: Quantum transport properties of exotic bilayer-graphene-based devices
Author: Lane, Thomas
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2019
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Bilayer graphene's remarkable conductivity and tunable band gap make it an excellent candidate for high quality electronic devices in the fields of quantum computation and valleytronics. In this thesis we present theoretical studies of a range of quantum transport devices comprised primarily of bilayer graphene, from quantum wires to tunnelling heterostructures. Utilising tight binding and recursive Green's function approaches we demonstrate two distinct transport regimes in electrostatically-confined one-dimensional bilayer graphene quantum wires. In one regime the wire has an approximately quadratic energy spectrum and exhibits regular, quantised conductance steps, whilst in the other the channel is semimetallic with non-monotonic regions in the lowest energy subbands. In this case, the `hole-like' states support standing waves along the length of the wire, precipitating resonance peaks on top of the first conductance step. Following this, we analytically explore the formation of localised ballistic channels, or `kink states', at delamination edges in bilayer graphene and at domain walls between regions with different sublattice potentials in monolayer graphene. We discover that these localised states, which in both cases span the induced energy gap, are valley polarised and occur across the electrostatic parameter space. Finally, we study resonant tunnelling between graphene/bilayer graphene electrodes separated by an insulating hexagonal boron nitride multilayer. We find that an angular misalignment between the two electrodes leads to a wealth of features in the tunnelling current characteristics including regions of negative differential conductance. The application of a magnetic field parallel to the plane of the device can be used to enforce unique momentum-conservation conditions around each pair of Brillouin zone corners. From this we identify the contribution to tunnelling current from each distinct valley and directly observe the chiral nature of Dirac electrons.
Supervisor: Falko, Vladimir ; Mishchenko, Artem Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: conductance ; chirality ; valley polarisation ; edge states ; quantum transport ; tunnelling heterostructures ; bilayer graphene ; graphene ; quantum point contacts