Abstract
Original language  English 

Awarding Institution 

Supervisors/Advisors 

Award date  24 Jun 2015 
Place of Publication  Enschede 
Publisher  
Print ISBNs  9789036538770 
DOIs  
Publication status  Published  24 Jun 2015 
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Keywords
 IR96110
 METIS310730
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Nontriviality matters: examining the interplay between swave superconductivity and topological surface states. / Snelder, M.
Enschede : Universiteit Twente, 2015. 102 p.Research output: Thesis › PhD Thesis  Research UT, graduation UT
TY  THES
T1  Nontriviality matters: examining the interplay between swave superconductivity and topological surface states
AU  Snelder, M.
PY  2015/6/24
Y1  2015/6/24
N2  The main focus of this thesis is to understand the correlations present at the swave/threedimensional topological insulator interface both theoretically and experimentally. In the future, devices containing these kind of interfaces can be used to create and manipulate a Majorana zeroenergy mode which serves as a building block for a topological quantum bit. In Chapter 1 the basics around quantum computation is considered and we show that the observation of a 4pi periodicity in a superconductor/topological insulator Josephson junction is the hallmark for the detection of a Majorana fermion mode. Chapter 2 studies in more detail the properties and conditions of the existence of this 4pi periodicity. We show that only one channel contributes to the 4pi periodicity but by exploiting the effect of magnetization, caused by a ferromagnet, the number of channels contributing to a 4pi period increases. Chapter 3 presents measurements on the topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) flakes. We show that at low temperatures the bulk conductance is neglible and that we succeeded to realize a Josephson supercurrent through the surface states. This is confirmed by the observation of a supercurrent and Fraunhofer pattern. Chapter 4 describes the calculations on the superconducting correlation present a the swave proximized topological surface states. We show that in the timereversal symmetry case there is an equal admixture of s and pwave correlations. As soon as timereversal symmetry is broken, pwave symmetry becomes dominant. The dominant pwave correlations cause the appearance of both a conductance dip a the gap energy and a conductance peak at zerobias. Chapter 5 combines the results of the previous chapters to study the conductance spectra on Au/BSTS/Nb devices. A conductance dip appears at the induced gap which could so far not be explained by trivial swave theory. In Chapter 6 we present a tight binding model of a threedimensional topological insulator to model the properties of a few quintuple layers. We were able to explain the kink observed in scanning tunneling spectroscopy data on a Bi2Te3 thin film by fitting the tight binding model to the density of states obtained by existing ab initio calculations.
AB  The main focus of this thesis is to understand the correlations present at the swave/threedimensional topological insulator interface both theoretically and experimentally. In the future, devices containing these kind of interfaces can be used to create and manipulate a Majorana zeroenergy mode which serves as a building block for a topological quantum bit. In Chapter 1 the basics around quantum computation is considered and we show that the observation of a 4pi periodicity in a superconductor/topological insulator Josephson junction is the hallmark for the detection of a Majorana fermion mode. Chapter 2 studies in more detail the properties and conditions of the existence of this 4pi periodicity. We show that only one channel contributes to the 4pi periodicity but by exploiting the effect of magnetization, caused by a ferromagnet, the number of channels contributing to a 4pi period increases. Chapter 3 presents measurements on the topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) flakes. We show that at low temperatures the bulk conductance is neglible and that we succeeded to realize a Josephson supercurrent through the surface states. This is confirmed by the observation of a supercurrent and Fraunhofer pattern. Chapter 4 describes the calculations on the superconducting correlation present a the swave proximized topological surface states. We show that in the timereversal symmetry case there is an equal admixture of s and pwave correlations. As soon as timereversal symmetry is broken, pwave symmetry becomes dominant. The dominant pwave correlations cause the appearance of both a conductance dip a the gap energy and a conductance peak at zerobias. Chapter 5 combines the results of the previous chapters to study the conductance spectra on Au/BSTS/Nb devices. A conductance dip appears at the induced gap which could so far not be explained by trivial swave theory. In Chapter 6 we present a tight binding model of a threedimensional topological insulator to model the properties of a few quintuple layers. We were able to explain the kink observed in scanning tunneling spectroscopy data on a Bi2Te3 thin film by fitting the tight binding model to the density of states obtained by existing ab initio calculations.
KW  IR96110
KW  METIS310730
U2  10.3990/1.9789036538770
DO  10.3990/1.9789036538770
M3  PhD Thesis  Research UT, graduation UT
SN  9789036538770
PB  Universiteit Twente
CY  Enschede
ER 