Regensburg 2007 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 44: Semiconductor Microcavities and Entangled States in Quantum Dots
HL 44.2: Hauptvortrag
Donnerstag, 29. März 2007, 14:30–15:00, H15
Electrical control of entangled excitons in self-assembled quantum dot molecules — •Hubert J. Krenner — Walter Schottky Institut, Technical University of Munich, 85748 Garching, Germany
In this talk I will discuss recent experiments in which we electrically manipulate coupled exciton states in individual QD-molecules (QDMs). The samples investigated consist of a single pair of vertically stacked self assembled In0.5Ga0.5As quantum dots embedded into the intrinsic region of an n-type GaAs Schottky photodiode. This device enables us to control the coherent coupling between exciton states in the upper and lower dots by tuning the electric field oriented along the axis of the QD-molecule via the gate voltage. New information is obtained on the charge distribution and spin structure of negatively charged trions in coupled quantum dot nanostructures and we directly probe Coulomb and Pauli blockade effects and inter-dot tunnel coupling using fully optical techniques. Electric field dependent µ-photoluminescence measurements reveal a clear anticrossing between spatially direct (e,h in the same dot) and indirect (e,h in different dots) neutral excitons with coupling energies in the range 2E1e+1h=1.2−3.2meV.1 Our experimental findings are shown to be in good accord with realistic calculations of the single exciton spectrum, confirming that the tunnel coupling is mediated by hybridization of the electron component of the exciton wavefunction over the two dots. In contrast, observations for negatively charged excitons are shown to be much richer due to the complex spectrum of negatively charged exciton states (X−1=2e+1h) that can exist in a QD-molecule.2 Both inter- and intra-dot Coulomb couplings are directly measured for a wide range of different charge initial X−ne, ne=0,1,2 states and the tunnel couplings and ground state spin configurations are tuned using electric field. Our findings are in good agreement with realistic calculations providing a fairly complete description of the behaviour of negatively charged excitons in quantum dot molecules.
1 H.J. Krenner et al. Phys. Rev. Lett. 94, 057402, (2005)
2 H.J. Krenner et al. Phys. Rev. Lett. 97, 076403, (2006)
Acknowledgements:
J. J. Finley, E. C. Clark, T. Nakaoka, C. Scheurer, M. Bichler and G. Abstreiter