Public defence in Engineering Physics, M.Sc. Marco Marín Suárez

Title of the doctoral thesis: Applications of hybrid single-electron turnstiles: To current standards and beyond

Doctoral student: Marco Marín Suárez
Opponent: Professor Andrew N. Cleland,University of Chicago, USA
Custos: Professor Jukka Pekola, Aalto University School of Science, Department of Applied Physics

In this thesis, we study hybrid single-electron transistors (SET) formed of a normal-metal island and superconducting leads. These are nanometer-scale systems operated at milikelvin temperatures. Such devices have been used in the past for generating single-electron currents by converting a radiofrequency signal into direct current. This turnstile of electrons is a suitable candidate for a standard for the ampere. After the redefinition of the SI, such standards have become intensively sought. 

We introduce new applications closely related to the current standard. First, we use this operation regime to show that superconducting excitations generated in the leads of the device can be extracted by Josephson junctions. Thanks to this, we found a reduction of one order of magnitude in the density of excitations. We come back to the redefinition of the SI and propose a new application of the turnstile operation as a standard for the watt. This is experimentally proved and its ultimate accuracy is fundamentally explored. With these, we show that the hybrid SET can emit single electrons with precisely defined amounts of energy synchronized with radiofrequency signals, in what we coined as frequency-to-power conversion. Next, we revisit the application as a current standard and show that a second signal can be used to modify the driving trajectories of the turnstile and still produce single-electron currents. By doing this, we block undesired tunneling events and improve the accuracy of the standard by one order of magnitude. Finally, such method is used for generating single-electron currents with zero-average voltage bias.

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

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Doctoral theses in the School of Science: https://aaltodoc.aalto.fi/handle/123456789/52