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Spectroscopy of Few-Electron Quantum Dots

100%

Heitmann D., Gudmundsson V., Rolf L., Schüller C., Steinebach C., Ulrichs E.

Acta Physica Polonica A

1999

vol. 96

issue 5

545-557

Advances in submicron technology make it possible to realize man-made low-dimensional electronic systems with quantum confined energy states. Superimposing lateral potential onto two-dimensional electron systems for example in AlGaAs-GaAs systems allows one to prepare quantum wires and dots. We will discuss modulation-doped systems. Then, with typical confinement energies in the meV regime, far-infrared and resonant Raman spectroscopy give direct access to the quantum confined energy levels of the systems. One is now approaching the limit to prepare quantum dots with well defined small numbers of electrons per dot, N = 1, 2, 3... It becomes thus possible to perform a kind of "atomic" spectroscopy in these systems.

Charged Excitons in the Quantum Hall Regime

84%

Schüller C., Broocks K., Schröter P., Heyn C., Heitmann D., Bichler M., Wegscheider W., Apalkov V., Chakraborty T.

Acta Physica Polonica A

2004

vol. 106

issue 3

341-353

We review our recent optical experiments on two-dimensional electron systems at temperatures below 1 K and under high magnetic fields. The two-dimensional electron systems are realized in modulation-doped GaAs-AlGaAs single quantum wells. Via gate electrodes the carrier density of the two-dimensional electron systems can be tuned in a quite broad range between about 1×10^{10} cm^{-2} and 2×10^{11} cm^{-2}. In dilute two-dimensional electron systems, at very low electron densities, we observe the formation of negatively charged excitons in photoluminescence experiments. In this contribution we report about the observation of a dark triplet exciton, which is observable at temperatures below 1 K and for electron filling factors <1/3, i.e., in the fractional quantum Hall regime only. In experiments where we have increased the density of the two-dimensional electron systems so that a uniform two-dimensional electron system starts to form, we have found a strong energy anomaly of the charged excitons in the vicinity of filling factor 1/3. This anomaly was found to exist in a very narrow parameter range of the density and temperature, only. We propose a model where we assume that localized charged excitons and a uniform Laughlin liquid coexist. The localized charged exciton in close proximity to the Laughlin liquid leads to the creation of a fractionally-charged quasihole in the liquid, which can account for the experimentally observed anomaly.

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2 Acta Physica Polonica A

1 2004

1 1999

2 Heitmann D.

2 Schüller C.

1 Apalkov V.

1 Bichler M.

1 Broocks K.

1 Chakraborty T.

1 Gudmundsson V.

1 Heyn C.

1 Rolf L.

1 Schröter P.

1 Steinebach C.

1 Ulrichs E.

1 Wegscheider W.

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Spectroscopy of Few-Electron Quantum Dots

Charged Excitons in the Quantum Hall Regime