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

Quantum Coherence and Mesoscopic Fluctuations

Markku Stenberg

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 September, 2007, at 12 o'clock noon.

Overview in PDF format (ISBN 978-951-22-8876-2)   [2065 KB]
Dissertation is also available in print (ISBN 978-951-22-8874-8)

Abstract

At low temperatures submicron-size structures may exhibit certain distinctive quantum features. These include, e.g., quantum interference effects, many-body correlation effects and different collective phenomena. At the borderline of the microscopic and macroscopic world resides a regime which is called mesoscopic. Mesoscopic systems are small enough to exhibit quantum coherent behavior, yet they contain a sufficiently large number of particles to allow a statistical description. Mesoscopic conductors may be considered as a realistic platform for information processing and future nanoelectronics since they allow for scalability and integration to larger circuits.

The charge transfers through disordered mesoscopic conductors exhibit different kinds of variations referred as mesoscopic fluctuations, e.g., noise, universal conductance fluctuations, and higher-order fluctuations. Containing information on the physics of the transport phenomenon not contained in conductance, these phenomena provide a delicate way to probe quantum coherence in disordered structures. Moreover, mesoscopic fluctuations can be used as a test bench for conventional condensed matter theories. In this Thesis, mesoscopic fluctuations are studied in order to extend the existing theories for the fluctuation point of view, for example, for the superconducting proximity effect, reflectionless tunneling, and weak localization.

When a normal metal is in contact with a superconductor, the superconducting proximity effect induces coherent correlations of electrons and holes in the former. Studying shot noise indicates that, in addition, the proximity effect induces anticorrelations between different electron-hole pairs in a normal metal. In this Thesis, for example, noise correlations in phase coherent normal-superconducting structures are investigated. In normal metals, weak localization behavior is considered. For example, a novel scaling relation for cumulants characterizing conductance fluctuations is found.

The quantum coherent phenomena considered in this Thesis have been studied by using three different kinds of theoretical approaches: the quasiclassical Keldysh Green's function formalism, the random matrix theory, and a numerical scattering approach.

This thesis consists of an overview and of the following 5 publications:

  1. Markku P. V. Stenberg and Jani Särkkä, Higher-order mesoscopic fluctuations in quantum wires: Conductance and current cumulants, Physical Review B 74, 035327 (2006). © 2006 American Physical Society. By permission.
  2. Markku P. V. Stenberg, Pauli Virtanen, and Tero T. Heikkilä, Phase-dependent noise correlations in normal-superconducting structures, Helsinki University of Technology, Publications in Engineering Physics A, Report TKK-F-A852 (2007) (submitted for publication). © 2007 by authors and © 2007 American Physical Society. By permission.
  3. Markku P. V. Stenberg and Tero T. Heikkilä, Nonlinear shot noise in mesoscopic diffusive normal-superconducting systems, Physical Review B 66, 144504 (2002). © 2002 American Physical Society. By permission.
  4. Tero T. Heikkilä, Markku P. Stenberg, Martti M. Salomaa, and Colin Lambert, Thermopower in mesoscopic normal-superconducting structures, Physica B 284-288, 1862 (2000). © 2000 Elsevier Science. By permission.
  5. Ari T. Alastalo, Markku P. V. Stenberg, and Martti M. Salomaa, Response functions of an artificial Anderson atom in the atomic limit, Journal of Low Temperature Physics 134, 897 (2004). © 2004 by authors and © 2004 Springer Science+Business Media. By permission.

Keywords: mesoscopics, phase coherence, full counting statistics, superconductivity, proximity effect

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© 2007 Helsinki University of Technology

Last update 2011-05-26