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Majorana Zero Modes: investigating implementations of nanowire/superconductor setups

Jardine, Malcolm (2023) Majorana Zero Modes: investigating implementations of nanowire/superconductor setups. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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This thesis aims to address some of the open questions surrounding the 1D semiconductor-nanowire/ superconductor hybrid system for investigating Majorana Zero Modes (MZMs), with focus on Ab Initio calculation of electronic properties of the semiconductor/superconductor interface and magnetic field implementation.
MZMs are zero-energy states localized near boundaries of 1D and 2D topological superconductors. They are of interest due to their potential use as topologically protected qubits for fault-tolerant quantum computing.
The semiconductor/ superconductor system, also called the hybrid system, could act as an effective p-wave superconductor which would harbor these MZM states.
This platform has many open questions: such as which materials are best to use, requiring tools such as density functional theory; and how to best implement the magnetic field, possibly done using micro-scale magnets.

The first topic of this thesis is how Density Functional Theory (DFT) is employed to investigate the effects of interfacing materials relevant to these hybrid system MZM experiments.
DFT is a computational approach used to approximately solve the electronic structure of condensed phase problems. We consider the materials $\alpha$-Sn, InSb and CdTe, among others. We investigate, using the DFT+U method, inserting a CdTe tunnel barrier as the proximity to the superconductor could adversely affect InSb’s properties. The results of DFT+U(BO) are validated against ARPES experiments for $\alpha$-Sn and CdTe. It is found that 16 monolayers ($\sim$ 3.5 nm) of CdTe provides an effective barrier between the InSb/$\alpha$-Sn interface.

Following this we investigate the need of relatively high external magnetic fields, that also changes direction for T-junction nanowire setups, in the MZM experimental approach. We propose devices that incorporate micromagnets to address this challenge. Numerical simulations of stray magnetic fields from micromagnet configurations are performed within the micromagnetic simulation software of MuMax3. This is combined with an effective MZM hybrid model and solved to find Majorana wavefunctions in the system. The devices proposed start with a four-magnet design to align magnetic field with the nanowire, and then scales up to nanowire T-junctions, where micromagnets provide the required magnetic field. The feasibility of the approach is assessed by performing magnetic imaging of prototype patterns.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Jardine, Malcolmmjj45@pitt.edumjj450000-0001-6206-3697
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairFrolov,
Committee MemberNoa,
Committee MemberThomas,
Committee MemberFrietas,
Committee MemberRoger,
Date: 6 September 2023
Date Type: Publication
Defense Date: 14 July 2023
Approval Date: 6 September 2023
Submission Date: 1 August 2023
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 135
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Majorana Zero Mode (MZM), semiconductor-nanowire/ superconductor hybrid device, density functional theory (DFT), electronic structure, angle resolved photoemission spectroscopy (ARPES), metal-semiconductor interface, Metal Induced Gap States (MIGS), tunnel barrier, InSb, CdTe, Sn, micromagnets
Date Deposited: 06 Sep 2023 16:30
Last Modified: 06 Sep 2023 16:30


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