Magnetometry by a proximity Josephson junction interferometer
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School of Science |
Doctoral thesis (article-based)
| Defence date: 2018-02-23
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Authors
Date
2018
Major/Subject
Mcode
Degree programme
Language
en
Pages
92 + app. 46
Series
Aalto University publication series DOCTORAL DISSERTATIONS, 34/2018
Abstract
In quantum technology, several aspects of superconductivity such as proximity effect have studied to develop a wide range of attractive applications at sub-kelvin temperatures. A new type of interferometer based on the proximity effect, taking place around transparent interfaces between normal- and superconducting metals, the Superconducting Quantum Interference Proximity Transistor (SQUIPT), relies on the phase dependence of the density of states in the proximized weak link. The SQUIPT devices offer the possibility to realize sensitive low-dissipation magnetometers compared to conventional DC SQUIDs. In this thesis, we investigate the development of the sensitive SQUIPT magnetometers. The first part of the thesis covers the characterization of non-hysteretic SQUIPTs with enhanced responsivity. In these structures, we demonstrate magnetic flux modulation of the device characteristics displaying no hysteresis at low temperatures by simply increasing the Josephson inductance of the weak link compared to self-inductance of the superconducting loop in the device. As a consequence, improvement in magnetic field responsivity is achievable. We then turn to the implementation of SQUIPT devices based on different fabrication methods and superconductor materials for improving the device performance. In this aspect, we fabricate and characterize niobium-based SNS devices utilizing two separate lithography and deposition steps with strong Ar ion cleaning in between. We further investigate a prototype hybrid SQUIPT device based on an Nb-Cu-Nb SNS junction with a conventional Al probe in tunnel junction. In the third part of the thesis, we present the flux noise characterization of a SQUIPT device using simultaneous measurement of DC transport properties and shot noise. To probe the noise, we use a cryogenic amplifier operating at frequencies in the range of a few MHz. We adapt this technique for flux noise measurements in SQUIPTs, adaptable also to low-temperature shot noise measurements of other nonlinear devices with high impedance. In order to investigate flux noise of SQUIPTs, we develop a model allowing one to optimize the figures of merit of the magnetometers such as the noise-equivalent flux.Description
Supervising professor
Pekola, Jukka P., Prof., Aalto University, Department of Applied Physics, FinlandThesis advisor
Peltonen, Joonas T., Dr., Aalto University, Department of Applied Physics, FinlandKeywords
superconductivity, proximity effect, SNS weak link, tunnel junction, SQUID, SQUIPT
Other note
Parts
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[Publication 1]: R. N. Jabdaraghi, M. Meschke, and J. P. Pekola. Non-hysteretic superconducting quantum interference proximity transistor with enhanced responsivity. Applied Physics Letters 104, 082601 (4 pages), February 2014.
DOI: 10.1063/1.4866584 View at publisher
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[Publication 2]: R. N. Jabdaraghi, J. T. Peltonen, O.-P. Saira, and J. P. Pekola. Low-temperature characterization of Nb-Cu-Nb weak links with Ar ion-cleaned interfaces. Applied Physics Letters 108, 042604 (5 pages), January 2016.
DOI: 10.1063/1.4940979 View at publisher
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[Publication 3]: R. N. Jabdaraghi, D. S. Golubev, J. P. Pekola, and J. T. Peltonen. Noise of a superconducting magnetic flux sensor based on a proximity Josephson junction. Scientific Reports 7, 8011 (13 pages), August 2017.
DOI: 10.1038/s41598-017-08710-7 View at publisher
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[Publication 4]: R. N. Jabdaraghi, J. T. Peltonen, D. S. Golubev, and J. P. Pekola. Magnetometry with Low-Resistance Proximity Josephson Junction. Journal of Low Temperature Physics, (10 pages), January 2018,
DOI: 10.1007/s10909-018-1863-x View at publisher