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3 Acta Physica Polonica A

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Electronic Shells of Dirac Fermions in Graphene Quantum Rings in a Magnetic Field

100%

Potasz P. , Güçlü A. , Hawrylak P.

Acta Physica Polonica A

2009

tom 116

nr 5

832-834

We present results of tight binding calculations demonstrating existence of degenerate electronic shells of Dirac fermions in narrow, charge neutral graphene quantum rings. We predict removal of degeneracy with finite magnetic field. We show, using a combination of tight binding and configuration interaction methods, that by filling a graphene ring with additional electrons this carbon based structure with half-filled shell acquires a finite magnetic moment.

Spectroscopy of Charged Donors and Many-Electron Effects in Semiconductor Quantum Wells

88%

McCombe B. , Jiang Z. , Tischler J. , Weinstein B. , Hawrylak P.

Acta Physica Polonica A

1999

tom 96

nr 5

559-572

Far infrared magnetospectroscopic studies of negative donor ions (D^{-}), and donors in the presence of many excess electrons in high magnetic fields in GaAs/AlGaAs quantum wells are reviewed. Both singlet and triplet transitions of well-center D^{-}ions were observed and are in good agreement with recent theoretical calculations. For off-well-center D^{-}ions evidence for a predicted magnetic-field-induced "unbinding" of the second electron was found. In the presence of many excess electrons the D^{-}singlet and -triplet transitions are blue-shifted substantially and evolve into bound magnetoplasmon excitations. Cusps are observed at integral and fractional Landau-level filling factors (ν) in a plot of normalized blue-shift of the D^{-}singlet-like bound magnetoplasmon transition vs. ν. For ν<1, the singlet-like bound magnetoplasmon transition continuously approaches the isolated D^{-}singlet transition with increasing magnetic field, while the triplet-like transition loses strength, irrespective of the electron density. Exact diagonalization studies of a donor ion with a few electrons in a parabolic lateral confining potential show the importance of electron-electron interactions and localization due to the long-range fluctuating potential in explaining this behavior. High pressure studies in a specially designed diamond anvil cell exhibit a continuous evolution from bound magnetoplasmon transitions to isolated D^{-}transitions to neutral donor transitions in a single sample as the pressure is increased and the electron density in the wells is decreased.

Influence of Configuration Mixing on Energies and Recombination Dynamics of Excitonic States in CdTe/ZnTe Quantum Dots

63%

Smoleński T. , Kazimierczuk T. , Goryca M. , Kossacki P. , Gaj J. , Wojnar P. , Fronc K. , Korkusiński M. , Hawrylak P.

nr 5

615-617

We study experimentally and theoretically excitonic recombination processes in CdTe/ZnTe quantum dots. The single quantum dot photoluminescence spectrum was observed and emission lines from X, X^-, X^+ and 2X excitonic states were identified. Experimental results were analysed in the theoretical model based on the effective mass approximation. Numerical calculations of energy positions and recombination probabilities of X, X^-, X^+ and 2X were performed. Computed results reproduce correctly the order and relative positions of emission lines and ratios of radiative lifetimes.