Many-body exciton states in self-assembled quantum dots coupled to a Fermi sea

Journal name:
Nature Physics
Volume:
6,
Pages:
534–538
Year published:
DOI:
doi:10.1038/nphys1673
Received
Accepted
Published online

Abstract

Many-body interactions give rise to fascinating physics such as the X-ray Fermi-edge singularity in metals, the Kondo effect in the resistance of metals with magnetic impurities and the fractional quantum Hall effect. Here we report the observation of striking many-body effects in the optical spectra of a semiconductor quantum dot interacting with a degenerate electron gas. A semiconductor quantum dot is an artificial atom, the properties of which can be controlled by means of a tunnel coupling between a metallic contact and the quantum dot. Previous studies concern mostly the regime of weak tunnel coupling, whereas here we investigate the regime of strong coupling, which markedly modifies the optical spectra. In particular we observe two many-body exciton states: Mahan and hybrid excitons. These experimental results open the route towards the observation of a tunable Kondo effect in excited states of semiconductors and are of importance for the technological implementation of quantum dots in devices for quantum information processing.

At a glance

Figures

  1. Photoluminescence of a single InAs/GaAs quantum dot in a charge-tunable device.
    Figure 1: Photoluminescence of a single InAs/GaAs quantum dot in a charge-tunable device.

    a, The measured photoluminescence spectrum of a quantum dot as function of gate voltage Vg. The colour scale relates linearly to the detector counts. The different exciton complexes are indicated. The steep photoluminescence lines at low energy correspond to the recombination of Mahan excitons (labelled as XMn). b, The line shapes for the neutral Mahan exciton XM0 at three different gate voltages. c, The line shape close to the onset of the X0 plateau (green open circles) and at the centre of the X0 plateau (orange filled circles). The corresponding voltages are indicated by the arrows in a.

  2. The two different mechanisms for the Mahan and hybrid excitons.
    Figure 2: The two different mechanisms for the Mahan and hybrid excitons.

    a, A schematic representation of the Mahan exciton. A hole in the quantum dot has a Coulomb interaction with the Fermi sea of electrons. The two possible optical recombination paths are indicated by (1) and (2). The initial (i) and final (f) states of the Mahan exciton are shown on the right corresponding to the state before and after recombination, respectively. The filled (open) circles correspond to the electron (hole). The back contact is represented by the coloured area and the dashed line indicates the Fermi energy level εF. There are many final states fn resulting from shake-up processes. b, A schematic representation of the hybrid exciton used to describe the tunnel coupling between the electron state in the quantum dot and the continuum of states in the back contact. On the right, i and f of the hybrid exciton are shown. Again there are many final states fn resulting from shake-up processes.

  3. Using the zero-bandwidth model, the X0 to X- transition can be reproduced.
    Figure 3: Using the zero-bandwidth model, the X0 to X transition can be reproduced.

    We used Vtun=0.4meV and included the Stark shift of excitons. The filled (blue) circles represent the energy positions determined from the experimental data and the red line is a fit using the zero-bandwidth model. The size of the open circles corresponds to the calculated intensity. The inset shows schematically the initial, i, and final, f, states.

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Author information

Affiliations

  1. Photonics & Semiconductor Nanophysics, COBRA, Eindhoven University of Technology, 5600 MB, PO Box 513, The Netherlands

    • N. A. J. M. Kleemans,
    • J. van Bree,
    • J. G. Keizer,
    • G. J. Hamhuis,
    • R. Nötzel,
    • A. Yu. Silov &
    • P. M. Koenraad
  2. Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA

    • A. O. Govorov

Contributions

N.A.J.M.K. and J.v.B. carried out the photoluminescence measurements. J.G.K. carried out the cross-sectional scanning tunnelling microscopy analysis. G.J.H. and R.N. grew the sample. A.O.G. carried out the theoretical calculations. N.A.J.M.K., J.v.B., A.O.G., A.Yu.S. and P.M.K. analysed and interpreted the data.

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The authors declare no competing financial interests.

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