The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

Mesoscopic Superconducting Tunnel Junction Devices: Experimental Studies of Performance Limitations

Jani Kivioja

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium F1 at Helsinki University of Technology (Espoo, Finland) on the 9th of June, 2005, at 12 noon.

Overview in PDF format (ISBN 951-22-7710-7)   [6702 KB]
Dissertation is also available in print (ISBN 951-22-7709-3)


In this work four different mesoscopic superconducting devices have been experimentally studied: an ammeter based on a hysteretic Josephson junction switching from the superconducting state to the normal state, a conventional Cooper pair pump (CPP) based on two superconducting islands separated by tunnel junctions, a novel flux assisted Cooper pair pump and a thermometer based on a tunnel junction between a superconductor and a normal metal. These devices make use of phenomena related to superconductivity and are also benefiting from some properties of small structures, e.g., of quantum mechanical tunneling and of transport of single electrons. The present research focused on investigating performance limitations of these devices and the aim was to improve their performance.

A hysteretic Josephson junction switching can be used as a sensitive current threshold detector. For many purposes, a smaller critical current Ic of the detecting junction would yield a higher current sensitivity. It was found in this Thesis that the main limitation of the ammeter is that with increasing sensitivity the negative effects due to dissipation start to dominate. In this Thesis the Josephson junction was also demonstrated as a shot-noise detector, and it was concluded that this kind of a device could probably be made into an absolute on-chip detector of Fano-factors and noise in general.

A charge pump is a device which can periodically transfer a discrete amount of charge Q through an electrical circuit. The measured double island CPP introduced a frequency dependent current with a value close to the expected one at low pumping frequencies. The drawback in the measurements was that the direction of the pumped current was set by the bias voltage. The results of the measurement on flux assisted pumping were indeed very promising and the studied device was able to produce sufficiently high pumped currents of around 0.1 nA with reasonable accuracy.

Thermometer based on NIS (Normal metal - Insulator - Superconductor) tunnel junctions is a very promising temperature sensor for bolometric radiation sensor applications. This work showed that it can be used as a sensitive thermometer up to MHz frequencies range and that its response time is limited by the electron-phonon scattering rate.

This thesis consists of an overview and of the following 7 publications:

  1. J. M. Kivioja, T. E. Nieminen, J. Claudon, O. Buisson, F. W. J. Hekking, and J. P. Pekola. 2005. Observation of transition from escape dynamics to underdamped phase diffusion in a Josephson junction. Physical Review Letters, accepted for publication; cond-mat/0501383. © 2005 by authors and © 2005 American Physical Society. By permission.
  2. J. M. Kivioja, T. E. Nieminen, J. Claudon, O. Buisson, F. W. J. Hekking, and J. P. Pekola. 2005. Weak coupling Josephson junction as a current probe: effect of dissipation on escape dynamics. New Journal of Physics, submitted for publication. © 2005 by authors and © 2005 Institute of Physics Publishing. By permission.
  3. J. P. Pekola, T. E. Nieminen, M. Meschke, J. M. Kivioja, A. O. Niskanen, and J. J. Vartiainen. 2005. Shot-noise-driven escape in hysteretic Josephson junctions. Physical Review Letters, submitted for publication; cond-mat/0502446. © 2005 by authors and © 2005 American Physical Society. By permission.
  4. J. J. Toppari, J. M. Kivioja, J. P. Pekola, and M. T. Savolainen. 2004. Turnstile behaviour of the Cooper pair pump. Journal of Low Temperature Physics 136, pages 57-91. © 2004 Springer Science+Business Media. By permission.
  5. A. O. Niskanen, J. M. Kivioja, H. Seppä, and J. P. Pekola. 2005. Evidence of Cooper-pair pumping with combined flux and voltage control. Physical Review B 71, 012513. © 2005 American Physical Society. By permission.
  6. J. M. Kivioja, I. J. Maasilta, J. P. Pekola, and J. T. Karvonen. 2003. Response time of a thermometer based on normal metal - insulator - superconductor (NIS) tunnel junctions. Physica E 18, pages 21-22. © 2003 Elsevier Science. By permission.
  7. L. J. Taskinen, J. M. Kivioja, J. T. Karvonen, and I. J. Maasilta. 2004. Direct measurement of the electron-phonon relaxation rate in thin copper films. physica status solidi (c) 1, pages 2856-2859.

Keywords: Josephson junction, phase diffusion, Cooper pair pump, NIS tunnel junction

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© 2005 Helsinki University of Technology

Last update 2011-05-26