AVS 46th International Symposium
    Nanometer-scale Science and Technology Division Monday Sessions
       Session NS2-MoA

Invited Paper NS2-MoA3
Quantum Dots; The Small World of Artificial Atoms

Monday, October 25, 1999, 2:40 pm, Room 6C

Session: Quantum Dots and Wires
Presenter: L.P. Kouwenhoven, Technical University of Delft, The Netherlands
Correspondent: Click to Email
We performed transport experiments on quantum dots in which the electron number can be tuned from 0 to 1, 2, etc. The addition spectrum shows a shell structure corresponding to a 2D harmonic confinement potential. The magnetic field dependence shows that the single particle states are spin degenerate and filled with two electrons. The filling of a shell occurs according to Hund's rule: electrons occupying degenerate states prefer to have parallel spins which lowers the total energy due to an increased exchange interaction. We observe such Hund's rule states at zero magnetic field and also at level crossings in a finite magnetic fields. In non-linear transport characteristics also the first few excited states are visible which we have studied over a magnetic field range up to 16 Tesla. The magnetic field induces transitions between ground states and excited states and also between excited states. In the high magnetic field regime all electrons are in the lowest orbital Landau level. This is the quantum Hall regime for a small electron system where the electrons form a strongly interacting many-body system. We have observed in the few-electron regime (N<10) so-called singlet-triplet oscillations. On increasing the magnetic field for a fixed electron number, we first observe spin-flips (between the two spin states of the lowest orbital Landau level), then the maximum density droplet (when all electrons are spin polarized and occupy the state with the lowest angular momentum), and then a reconstruction (probably an edge reconstruction, either spin polarized or with a spin texture). @FootnoteText@Work done in collaboration with D. Austing, M. Eto, T. Honda, S. Tarucha, M. Danoesastro, J. Janssen, R. van der Hage, and T. Oosterkamp.