Thesis

One-dimensional quantum transport phenomena in periodically modulated electron waveguides

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Awarding institution
  • University of Strathclyde
Date of award
  • 2024
Thesis identifier
  • T17057
Person Identifier (Local)
  • 201889178
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • The study of quantum transport in one dimension is of great interest in many areas of condensed matter physics. This thesis is motivated by conductance measurements in modulated LAO/STO nanowires, where a strong conductance baseline of 2e 2/h is observed when a Kronig-Penney potential is applied, which survives up to external magnetic fields > 18 T. This is also observed when the nanowire is helically modulated, but an additional feature is the appearance of conductance oscillations above the 2e 2/h baseline which occur at lower energies than the 4e 2/h peak. In order to model this, we begin by constructing an electron waveguide model for the nanowire formed at the LAO/STO interface. We then include the effect of periodic modulations and associated spin-orbit coupling resulting from these, and analyse the resulting band structure and conductance, finding that a single electron model is not sufficient to explain the 2e 2/h baseline. This was found in previous work, and the solution is to include electron-electron interactions. To include the effects of these, we begin with a standard BCS-like mean-field model. To study first the effect coming from a periodic modulation of the potential in the waveguide (vertical modulation), we introduce only the associated spin-orbit coupling to this model. We find that this leads to enhanced pairing, and could potentially explain the strong baseline of 2e 2/h. Additionally, we look only at the effect of a periodic modulation in the centre of the nanowire (lateral modulation), which we find introduces triplet pairing in the waveguide region. Combining these two modulations together, we extend the mean-field model again to include the form of the modulation potential alongside associated spin-orbit couplings to study the helical waveguide. We observe enhanced pairing and triplet pairing simultaneously. To study the oscillations in conductance, we introduce a phenomenological pair scattering model where triplet pairs incedent on the interface between helical and unmodulated regions can backscatter. We find that this model can indeed produce oscillations above the 2e 2/h baseline.
Advisor / supervisor
  • Daley, Andrew
Resource Type
DOI

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