Sammanfattning
In this thesis, we study quantum transport properties of superconductorsemiconductor nanowire hybrid devices. We mainly focus on the quantum transport in InSb nanowire Josephson quantum dot devices, i.e. quantum dots coupled to two pieces of superconductors. In such a structure, manybody interacting phenomena occur, such as Kondo correlation, multiple Andreev reflection, and the formation of Andreev bound states (ABSs) and Majorana bound states (MBSs).
InSb nanowire is an ideal candidate for electronic and spintronic applications. Among all of the binary IIIV semiconductors, InSb (bulk) has the narrowest band gap (E_{g}∼0.17 eV), the highest electron mobility (μ_{e}∼77,000 cm^{2}V^{1}s^{1}), the smallest effective electron mass (m*∼0.014 m_{e}), the largest electron g^{*}factor (g^{*}∼51), and the largest spinorbit interaction (α up to 100 meV·nm). InSb nanowire is therefore predicted to be a promising harbouring system for MBSs  a key ingredient for topological quantum computing  when it is coupled to a swave superconductor.
When an InSb nanowire is coupled to two swave superconductor leads (Al or Nb in this thesis), a quantum dot is naturally formed in the nanowire segment between the superconductors. Such a device can be configured to various regimes upon applying different strength of external electrical field and magnetic field. In particular, with a Zeeman field perpendicularly applied to the spinorbit field direction, the device is predicted to host two pairs of MBSs mediated by the interquantumdot, which will give rise to a zerobias conductance peak (ZBCP) in the tunnelling spectrum as a signature of MBSs.
However, except MBSs, other trivial mechanism can also cause emergent ZBCPs in a magnetic field, e.g. recovered Kondo resonances by a magnetic field, ABSs at quantum phase transition, etc. We hence take the emergent ZBCPs in magnetic field, both trivial and nontrivial, as the main thread of this thesis. We explore their physical origins and related physics with the main focuses on transport features in the Kondosuperconductor competing regime, lead state detection via a ptype quantum dot, anomalous negative magnetoresistance with Kondo correlations, and parityindependent ZBCPs. These measurements and discussion aim to be one step closer of the understandings of how a single magnetic impurity interacts with a superconductor, how to distinguish topologically trivial/nontrivial physics, and unveil more novel physics in the Josephson quantum dot structures.
InSb nanowire is an ideal candidate for electronic and spintronic applications. Among all of the binary IIIV semiconductors, InSb (bulk) has the narrowest band gap (E_{g}∼0.17 eV), the highest electron mobility (μ_{e}∼77,000 cm^{2}V^{1}s^{1}), the smallest effective electron mass (m*∼0.014 m_{e}), the largest electron g^{*}factor (g^{*}∼51), and the largest spinorbit interaction (α up to 100 meV·nm). InSb nanowire is therefore predicted to be a promising harbouring system for MBSs  a key ingredient for topological quantum computing  when it is coupled to a swave superconductor.
When an InSb nanowire is coupled to two swave superconductor leads (Al or Nb in this thesis), a quantum dot is naturally formed in the nanowire segment between the superconductors. Such a device can be configured to various regimes upon applying different strength of external electrical field and magnetic field. In particular, with a Zeeman field perpendicularly applied to the spinorbit field direction, the device is predicted to host two pairs of MBSs mediated by the interquantumdot, which will give rise to a zerobias conductance peak (ZBCP) in the tunnelling spectrum as a signature of MBSs.
However, except MBSs, other trivial mechanism can also cause emergent ZBCPs in a magnetic field, e.g. recovered Kondo resonances by a magnetic field, ABSs at quantum phase transition, etc. We hence take the emergent ZBCPs in magnetic field, both trivial and nontrivial, as the main thread of this thesis. We explore their physical origins and related physics with the main focuses on transport features in the Kondosuperconductor competing regime, lead state detection via a ptype quantum dot, anomalous negative magnetoresistance with Kondo correlations, and parityindependent ZBCPs. These measurements and discussion aim to be one step closer of the understandings of how a single magnetic impurity interacts with a superconductor, how to distinguish topologically trivial/nontrivial physics, and unveil more novel physics in the Josephson quantum dot structures.
Originalspråk  engelska 

Kvalifikation  Doktor 
Tilldelande institution 

Handledare 

Tilldelningsdatum  2018 sep. 6 
Förlag  
ISBN (tryckt)  9789177538165 
ISBN (elektroniskt)  9789177538172 
Status  Published  2018 sep. 6 
Bibliografisk information
Defence detailsDate: 20181002
Time: 09:15
Place: Rydbergsalen, Fysicum, Sölvegatan 14, Lund University, Faculty of Engineering LTH.
External reviewer(s)
Name: Brinkman, Alexander
Title: Professor
Affiliation: University of Twente, The Netherlands

Ämnesklassifikation (UKÄ)
 Teknik och teknologier
 Naturvetenskap