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.
Aalto

Nonequilibrium and Transport in Proximity of Superconductors

Pauli Virtanen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium K216 at Helsinki University of Technology (Espoo, Finland) on the 22nd of October, 2009, at 12 noon.

Overview in PDF format (ISBN 978-952-248-086-6)   [2292 KB]
Dissertation is also available in print (ISBN 978-952-248-085-9)

Abstract

Mesoscopic physics studies systems that are larger than atoms but small enough to exhibit quantum coherent effects. Thanks to improved fabrication techniques, study of superconductivity and its effect on contacted materials in tailored micrometer-scale mesoscopic structures has become possible in the recent decades. Electron transport, non-equilibrium response, thermoelectricity, and fluctuations in such devices have attained significant interest. Thermoelectric effects in particular are one of the least understood aspects of superconductivity. Quantitative understanding of the observations in the mesoscopic regime has turned out to require quantum-mechanical models. Devices based on mesoscopic superconductivity have also technological applications, in addition to being of primary scientific interest.

This thesis discusses theoretical studies on thermoelectric and out-of-equilibrium effects in superconducting proximity structures. Green function methods are applied for computing the thermoelectric and nonequilibrium response of mesoscopic structures to external driving. The results explain several features observed in experiments, and clarify one origin of thermoelectricity in the studied systems.

Electrical fluctuations in mesoscopic structures are also discussed, and a device for characterizing the statistics and spectrum of the fluctuations is proposed. This mesoscopic on-chip detector is based on a superconducting Josephson junction in the Coulomb blockade regime. It is expected to bypass problems in conventional measurements of higher-order statistics of noise. That the detector can be manufactured close to the measured mesoscopic noise source could also enable studies of quantum properties in the higher-order statistics of the fluctuations.

This thesis consists of an overview and of the following 10 publications:

  1. Pauli Virtanen and Tero T. Heikkilä. 2004. Thermopower induced by a supercurrent in superconductor–normal-metal structures. Physical Review Letters, volume 92, number 17, 177004. © 2004 American Physical Society. By permission.
  2. Pauli Virtanen and Tero T. Heikkilä. 2004. Thermopower in Andreev interferometers. Journal of Low Temperature Physics, volume 136, numbers 5-6, pages 401-434. © 2004 Springer Science+Business Media. By permission.
  3. M. S. Crosser, Pauli Virtanen, Tero T. Heikkilä, and Norman O. Birge. 2006. Supercurrent-induced temperature gradient across a nonequilibrium SNS Josephson junction. Physical Review Letters, volume 96, number 16, 167004. © 2006 American Physical Society. By permission.
  4. J. Zou, I. Sosnin, P. Virtanen, M. Meschke, V. T. Petrashov, and T. T. Heikkilä. 2007. Influence of supercurrents on low-temperature thermopower in mesoscopic N/S structures. Journal of Low Temperature Physics, volume 146, numbers 1-2, pages 193-212. © 2006 Springer Science+Business Media. By permission.
  5. Pauli Virtanen and Tero T. Heikkilä. 2007. Peltier effects in Andreev interferometers. Physical Review B, volume 75, number 10, 104517. © 2007 American Physical Society. By permission.
  6. P. Virtanen and T. T. Heikkilä. 2007. Thermoelectric effects in superconducting proximity structures. Applied Physics A: Materials Science & Processing, volume 89, number 3, pages 625-637. © 2007 Springer Science+Business Media. By permission.
  7. P. Virtanen, J. Zou, I. Sosnin, V. T. Petrashov, and T. T. Heikkilä. 2007. Phase states of multiterminal mesoscopic normal-metal–superconductor structures. Physical Review Letters, volume 99, number 21, 217003. © 2007 American Physical Society. By permission.
  8. M. S. Crosser, Jian Huang, F. Pierre, Pauli Virtanen, Tero T. Heikkilä, F. K. Wilhelm, and Norman O. Birge. 2008. Nonequilibrium transport in mesoscopic multi-terminal SNS Josephson junctions. Physical Review B, volume 77, number 1, 014528. © 2008 American Physical Society. By permission.
  9. Tero T. Heikkilä, Pauli Virtanen, Göran Johansson, and Frank K. Wilhelm. 2004. Measuring non-Gaussian fluctuations through incoherent Cooper-pair current. Physical Review Letters, volume 93, number 24, 247005. © 2004 American Physical Society. By permission.
  10. P. Virtanen and T. T. Heikkilä. 2006. Circuit theory for noise in incoherent normal-superconducting structures. New Journal of Physics, volume 8, number 4, 50. © 2006 Institute of Physics Publishing and © 2006 Deutsche Physikalische Gesellschaft. By permission.

Keywords: mesoscopic physics, superconducting proximity effect

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© 2009 Helsinki University of Technology

Last update 2011-05-26