Speaker
Dr. HeeDae Kim
Hokkaido University
Date 2017.03.06(Mon)
Time 14:00
Place S4-625
Abstract:
Currently, quantum ring (QR) structures are of great interest for the optical Aharonov-Bohm (AB) effect. While the rotating charge in the shell of a type-II quantum dot (QD) determines the AB oscillation period, the orbital radius difference of the electrons and holes is the crucial parameter in a QR. Nevertheless, the individual behavior of each of the particles is not clear in a QR. In addition, while the optical AB oscillations were easily measured in type-II quantum dot ensembles, the AB oscillations of neutral exciton in a single QR were rarely observed. Recent measurements have shown that the morphology of a QR is anisotropic, where the rim height is not constant around the azimuthal angle based on atomic atomic force microscope (AFM) images of a QR. We observed the presence of strongly localized states arises from the volcano-like QR structure, which corresponds to an excited states of the vertical confinement. The asymmetry was investigated in terms of the polarization dependence of excitons and biexcitons, where a large energy difference (~0.8meV) in the exciton emission energy for perpendicular polarizations was observed and the oscillator strengths were also compared using the photoluminescence decay rate. For perpendicular polarizations, the biexciton exhibits twice the energy difference seen for the exciton, a fact that may be attributed to a possible change in the selection rules for the lowered symmetry.
Additionally, I have observed novel oscillations of a strongly correlated exciton pair, similar to a Wigner molecule, in a single QR, where the emission energy changes abruptly at the transition magnetic field with a fractional oscillation period compared to that of the exciton, a so-called fractional optical Aharonov-Bohm oscillation.