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You searched for subject:(Multiple Andreev reflection). Showing records 1 – 2 of 2 total matches.

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1. Law Toner, Stephanie. Magnetotransport in superconductor to semiconductor junctions: multiple Andreev reflections and coupling to quantum hall states.

Degree: PhD, 0240, 2012, University of Illinois – Urbana-Champaign

Two-dimensional electron gases (2DEGs) and superconductors share many interesting properties. Both exhibit dissipationless current flow as well as strong electron correlations which can lead to a new ground state charge carrier. In this work, coupling between superconductors and 2DEGs was studied. Using band structure engineering as well as InGaAs and InAs caps, junctions were fabricated in which the superconductor was extremely well-coupled to the semiconductor. The superconducting contacts were separated by a small gap whose length varied from 100nm to 1000nm. For devices capped with InGaAs and a long junction length, a zero bias resistance maximum was seen. In these devices, the maximum increased when the sample was in a quantum Hall state due to the reduction in the number of conduction channels. Samples with a shorter length showed a zero bias resistance minimum when the magnetic field was tuned between quantum Hall states and a maximum otherwise. The minimum is a precursor to a supercurrent. Device were also made with higher transparency InAs caps. One set of devices had an array of small superconducting shorts bridging the gaps. When the sample was in an even filling factor state, a large supercurrent and a sharp transition to the normal state was seen when current was applied in the direction of the edge states. Conversely, when current was applied against the edge states, a smaller supercurrent with a very broad and noisy transition to the normal state was observed. Behavior was reversed when the sample was in an odd filling factor state and when the field was applied in the negative direction. The broad, noisy transition is a result of flux flow behavior. The interaction of the edge state with the sample lowered the barriers to flux motion in one direction, resulting in an asymmetric superconducting flux flow transistor. Devices with InAs caps and no shorts showed peaks in differential resistance due to multiple Andreev reflection. As the magnetic field is increased, the MAR peaks move toward lower voltages and disappear. The movement of the peaks is caused by the decrease of the superconducting gap with field. Advisors/Committee Members: Eckstein, James N. (advisor), Mason, Nadya (Committee Chair), Eckstein, James N. (committee member), Fradkin, Eduardo H. (committee member), Stack, John D. (committee member).

Subjects/Keywords: superconductors; quantum Hall edge modes; multiple Andreev reflection; vortex motion

…observed a wealth of interesting behavior including Andreev reflection[5, 6], multiple… …devices which allowed me to investigate the dependence of multiple Andreev reflection on… …multiple Andreev reflection, transport mediated via quantum Hall edge states, and controllable… …multiple Andreev reflection. The voltage of each peak was measured as a function of magnetic… …reflection, multiple Andreev reflection, and the resistively and capacitively shunted junction… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Law Toner, S. (2012). Magnetotransport in superconductor to semiconductor junctions: multiple Andreev reflections and coupling to quantum hall states. (Doctoral Dissertation). University of Illinois – Urbana-Champaign. Retrieved from http://hdl.handle.net/2142/31194

Chicago Manual of Style (16th Edition):

Law Toner, Stephanie. “Magnetotransport in superconductor to semiconductor junctions: multiple Andreev reflections and coupling to quantum hall states.” 2012. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed February 26, 2020. http://hdl.handle.net/2142/31194.

MLA Handbook (7th Edition):

Law Toner, Stephanie. “Magnetotransport in superconductor to semiconductor junctions: multiple Andreev reflections and coupling to quantum hall states.” 2012. Web. 26 Feb 2020.

Vancouver:

Law Toner S. Magnetotransport in superconductor to semiconductor junctions: multiple Andreev reflections and coupling to quantum hall states. [Internet] [Doctoral dissertation]. University of Illinois – Urbana-Champaign; 2012. [cited 2020 Feb 26]. Available from: http://hdl.handle.net/2142/31194.

Council of Science Editors:

Law Toner S. Magnetotransport in superconductor to semiconductor junctions: multiple Andreev reflections and coupling to quantum hall states. [Doctoral Dissertation]. University of Illinois – Urbana-Champaign; 2012. Available from: http://hdl.handle.net/2142/31194


University of Lund

2. Deng, Mingtang. Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors.

Degree: 2013, University of Lund

This thesis focuses on charge transport in semiconductor InSb nanowire quantum devices, including the electron transport, the hole transport, and the Cooper pair transport. Devices in which InSb semiconductor nanowire quantum dots are coupled with normal metals, superconductors or the proximity effect induced topological superconductors are fabricated and measured. Firstly, we have fabricated and measured normal metal contacted InSb nanowire devices. In each of these devices, a quantum dot is formed in the InSb nanowire between the contacts. We report on the magnetotransport measurements performed to these quantum dot devices, and reveal several novel transport features. First, we demonstrate the ambipolar quantum dot devices in which the quantum dots can be tuned from the n-type regime to the p-type regime. The transport measurements in both of the n-type regime and the p-type regime are performed. We also show that two methods can be used to estimate the effective g-factor of the quantum dot, but they can give very different estimation in the presence of a Kondo effect. In the p-type regime of an ambipolar quantum dot, we observe conductance peaks in the stability diagram which can be attributed to the quasi-1D lead states. Secondly, we have fabricated and characterized the superconductor coupled InSb nanowire quantum dots. We probe the density of states of the quasi-particles in the superconductor contacts, via a weakly coupled InSb quantum dot. In the strongly coupled InSb nanowire-superconductor junctions, dissipationless Josephson currents are observed. A SQUIDS device is also fabricated and measured, in which an anomalous modulation of the Josephson current in the magnetic field is observed. In the medium coupling regime, we observe the signatures of the multiple Andreev reflections, the sub-gab bound states, and the Josephson current, interplaying with the Kondo effect. By adjusting the gate voltages, we can control the dot-lead coupling strength and asymmetry. Here, we report the quantum phase transition induced by tuning the dot-lead coupling and the quantum phase transition induced by a magnetic field. We have also found the coupling asymmetry is very important for the observation of the Josephson current. In the magnetic field, the evolution of the Kondo effect enhanced Josephson current is found to be strongly dependent on the energy ratio of Kondo energy and superconducting gap. Finally, an anomalous low-field suppression of the zero-bias conductance peak in the Kondo regime is observed. In the last part of the thesis, we report on our efforts to search for Majorana fermions in solid state systems. Nb-InSb nanowire quantum dot-Nb hybrid devices were fabricated and the transport measurements were performed at low temperatures for these devices. We have observed anomalous zero-bias conductance peaks emerging in finite magnetic fields in the Nb-InSb nanowire quantum dot-Nb hybrid devices as a signature of the Majorana bound states in such hybrid devices. We have also found that the zero-bias conductance…

Subjects/Keywords: Condensed Matter Physics; Multiple Andreev reflection; SQUID; Proximity effect; the Josephson effect; Cooper pair; the Kondo effect; the Zeeman effect; Quantum dot; InSb; Nanowires; Transport; Fysicumarkivet A:2013:Deng; Majorana bound state; Yu-Shiba-Rusinov state; Andreev bound state

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Deng, M. (2013). Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors. (Doctoral Dissertation). University of Lund. Retrieved from https://lup.lub.lu.se/record/4024868 ; https://portal.research.lu.se/ws/files/6267623/4024941.pdf

Chicago Manual of Style (16th Edition):

Deng, Mingtang. “Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors.” 2013. Doctoral Dissertation, University of Lund. Accessed February 26, 2020. https://lup.lub.lu.se/record/4024868 ; https://portal.research.lu.se/ws/files/6267623/4024941.pdf.

MLA Handbook (7th Edition):

Deng, Mingtang. “Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors.” 2013. Web. 26 Feb 2020.

Vancouver:

Deng M. Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors. [Internet] [Doctoral dissertation]. University of Lund; 2013. [cited 2020 Feb 26]. Available from: https://lup.lub.lu.se/record/4024868 ; https://portal.research.lu.se/ws/files/6267623/4024941.pdf.

Council of Science Editors:

Deng M. Charge Transport in Semiconductor Nanowire Quantum Devices: From Single Quantum Dots to Topological Superconductors. [Doctoral Dissertation]. University of Lund; 2013. Available from: https://lup.lub.lu.se/record/4024868 ; https://portal.research.lu.se/ws/files/6267623/4024941.pdf

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