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

Few-Electron Quantum Dot Molecules

Meri Helle

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 E at Helsinki University of Technology (Espoo, Finland) on the 5th of January, 2006, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7986-X)   [4150 KB]
Dissertation is also available in print (ISBN 951-22-7985-1)

Abstract

Semiconductor quantum dots have been studied for nearly two decades with a variety of experimental and theoretical methods. The typical dimensions of these "artificial atoms" are from a hundred nanometers to one micrometer and the number of electrons inside the quantum dots can range from one to several hundred. The tunable size, shape and electron number, as well as the enhanced electron correlation and magnetic field effects, makes quantum dots excellent objects for studying fascinating many-electron quantum physics in a controlled way. In the rapidly growing fields of nanoscience and nanotechnology, quantum dots are promising candidates for future nanoelectronic devices. One of the most intriguing scenarios of quantum dot applications lies in the utilization of an electron spin as a quantum bit in quantum computing.

This Thesis deals with the modeling of electron states in two-dimensional coupled quantum dots or quantum-dot molecules. The emphasis is on describing electron correlations properly but concentrating only on a few electrons inside the quantum-dot molecules. In this Thesis we mostly consider two interacting electrons and find remarkably complex behavior as a function of the magnetic field. We find the electron-electron interactions and the shape of the confining potential to have a profound effect on the two-electron quantum states.

The main results of this Thesis are the calculations and analysis of the quantum-mechanical states of two electrons in a magnetic field. This includes the ground-state transitions and magnetizations of the system as a function of magnetic field and careful analysis of the wave functions and the calculation and analysis of the far-infrared magneto-optical absorption spectra. We also study classical electrons in a quantum-dot molecule. This is relevant for the Wigner crystallization of electrons in a very high magnetic field or in a very low electron density.

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

  1. M. Marlo, M. Alatalo, A. Harju, and R. M. Nieminen, Lateral diatomic two-dimensional artificial molecules: Classical transitions and quantum-mechanical counterparts, Physical Review B 66, 155322 (2002) (7 pages). © 2002 American Physical Society. By permission.
  2. M. Marlo, A. Harju, and R. M. Nieminen, Role of interactions in the far-infrared spectrum of a lateral quantum-dot molecule, Physical Review Letters 91, 187401 (2003) (4 pages). © 2003 American Physical Society. By permission.
  3. M. Marlo-Helle, A. Harju, and R. M. Nieminen, Singlet-triplet oscillations and far-infrared spectrum of four-minima quantum-dot molecule, Physica E 26, 286 (2005) (5 pages). © 2005 Elsevier Science. By permission.
  4. M. Helle, A. Harju, and R. M. Nieminen, Two-electron lateral quantum-dot molecules in a magnetic field, Physical Review B 72, 205329 (2005) (24 pages). © 2005 American Physical Society. By permission.
  5. M. Helle, A. Harju, and R. M. Nieminen, Far-infrared spectra of lateral quantum dot molecules, New Journal of Physics (2005) (17 pages), cond-mat/0511577, submitted for publication.

Keywords: semiconductor quantum dots, magnetic field, far-infrared absorption, exact diagonalization

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© 2006 Helsinki University of Technology

Last update 2011-05-26