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

Influence of Electromagnetic Environment in Single Tunnel Junctions

Jari Penttilä

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 7th of April, 2001, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-5412-3)   [4856 KB]
Dissertation is also available in print (ISBN 951-22-5388-7)

Abstract

In this thesis, electron transport through single tunnel junction embedded in a dissipative environment was studied both in normal and superconducting state. High-voltage asymptotics of the current voltage (IV) characteristics for small normal tunnel junctions and carbon nanotubes were studied experimentally. Power-law voltage tails of IV curve were detected when approaching the linear law V = IR + e/2C at large voltages with the offset depending of the junction capacitance C.

The effect of environment is in fact a result of Johnson-Nyquist noise in the electric circuit. In our low temperature measurements, the power-law tails at high voltages are connected only with the quantum part of Johnson-Nyquist noise. Thus, detection of these tails in a good agreement with the quantum theory of environment is a rather unique verification of quantum zero-point fluctuations in macroscopic systems.

Our experimental conditions included the case of strong tunneling when the junction resistance RT was less than the quantum resistance RK. The strong-tunneling corrections to the environmental modes at high voltages can be simply incorporated by including the junction resistance RT into the effective electric circuit for calculation of the quantum noise.

In the superconducting state, our experiments for the first time clearly confirm the existence of the dissipative phase transition in a single Josephson junction. In the transition, dissipation destroys the quantum mechanical band structure and restores the classical Josephson behaviour of dynamics governed by the classical phase difference φ.

The observed phase diagram differed from that expected originally. The agreement with theory was achieved by taking into account that the position of the measured phase boundary is governed not only by intrinsic junction parameters, but also by the accuracy of voltage measurement. Our work is a strong demonstration of quantum effects in a single Josephson junction, especially, of the Josephson phase delocalization and the band picture of phase motion.

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

  1. J. Penttilä, Ü. Parts, P. Hakonen, M. Paalanen, and E. Sonin, "Superconductor-Insulator Transition" in a Single Josephson Junction, Physical Review Letters 82, 1004 (1999).
  2. J. Penttilä, P. Hakonen, M. Paalanen, and E. Sonin, Experiments on Dissipative Dynamics of Single Josephson Junctions, Report TKK-KYL-003 (2001).
  3. J. Penttilä, P. Hakonen, M. Paalanen, Ü. Parts, and E. Sonin, Dissipative Phase Transition in a Mesoscopic Josephson Junction in a Weak Magnetic Field, Physica B 284-288, 1832 (2000).
  4. J. Penttilä, P. Hakonen, M. Paalanen, Ü. Parts, and E. Sonin, Phase Diagram of Superconductor-Insulator Transition in a Single Josephson Junction, in Quantum Physics at Mesoscopic Scale, Proceedings of the XXXIVth Rencontres de Moriond (EDP Sciences, 2000) p. 345.
  5. J. Penttilä, Ü. Parts, P. Hakonen, M. Paalanen, and E. Sonin, Effect of Quantum Noise on Coulomb Blockade in Normal Tunnel Junctions at High Voltages, Physical Review B 61, 10890 (2000).
  6. J. Penttilä, P. Hakonen, M. Paalanen, Ü. Parts, and E. Sonin, Asymptotic Behavior of a Normal Tunnel Junction at Large Voltages, Physica B 280, 399 (2000).
  7. R. Tarkiainen, M. Ahlskog, J. Penttilä, L. Roschier, M. Paalanen, E. Sonin, and P. Hakonen, Multiwalled Carbon Nanotubes as High Impedance Transmission Lines, Report TKK-KYL-004 (2001).
  8. L. Roschier, J. Penttilä, M. Martin, P. Hakonen, M. Paalanen, U. Tapper, E. Kauppinen, C. Journet, and P. Bernier, Single-electron Transistor Made of Multiwalled Carbon Nanotube Using Scanning Probe Manipulation, Applied Physics Letters 75, 728 (1999).
  9. P. Hakonen, J. Ikonen, Ü. Parts, J. Penttilä, L. Roschier, and M. Paalanen, Noise of a Single Electron Transistor on a Si3N4 Membrane, Journal of Applied Physics, 86, 2684 (1999).
  10. P. Hakonen, M. Kiviranta, J. Penttilä, and M. Paalanen, Noise Measurements on Single Electron Transistors Using Bias Switching Read-out, The European Physical Journal Applied Physics, 11, 227 (2000).

Keywords: electron transport in mesoscopic systems, Josephson effects, Coulomb blockade

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© 2001 Helsinki University of Technology

Last update 2011-05-26