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Transporteigenschaften von Quantenpunkten

Friedrich Simmel

ISBN 978-3-89722-276-2
168 Seiten, Erscheinungsjahr: 1999
Preis: 40.00 €
A quantum dot is a small electronic island coupled to reservoirs via tunneling barriers. At low temperatures transport through such an island is blocked due to the mutual electrostatic repulsion of the electrons. However, variation of the electrochemical potential of the island using capacitively coupled control gates can lift this so-called "Coulomb blockade" (CB). This results in oscillations of the conductance of the system.

In the present work quantum dot systems are electrostatically defined within GaAs/AlGaAs heterostructures utilizing electron beam written electrodes. Electronic transport measurements are performed at ultra-low temperatures in a He-3/He-4 dilution refrigerator. Coulomb blockade oscillations are measured and analyzed from three different viewpoints:

The statistical properties of the conductance oscillations of quantum dots are investigated and compared to predictions of random matrix theory (RMT). For both gallium arsenide and silicon quantum dot systems the distribution of the conductance peak spacings deviates from the RMT-prediction. The fluctuations are governed by the strength of the electron-electron interaction, not by the single particle energy level spacing as expected from RMT.

Nonlinear transport spectroscopy is performed on a very small quantum dot system. From the bias and gate voltage dependence of the conductance of the quantum dot information about the electronic excitations of the system is obtained. Appropriate tuning of the tunneling barriers brings sets the quantum dot in the Kondo regime. A conductance anomaly is observed an non-zero bias. This anomaly can be explained as an anomalous Kondo effect in a system with asymmetric and energy dependent tunneling barriers.

Finally, the influence of high frequency radiation on the transport properties of quantum dots is investigated. In transport measurements under external microwave irradiation photon assisted tunneling is observed which results in photonic sidebands of the Coulomb blockade oscillations. An alternative experimental setup combines a double quantum dot system with a Josephson junction. The ac Josephson effect is utilized for chip-integrated microwave generation.

Keywords:
  • Halbleiterphysik
  • Nanotechnologie
  • Quantenpunkte

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