Letter abstract
Nature Physics 4, 467 - 471 (2008)
Published online: 20 April 2008 | doi:10.1038/nphys944
Subject Categories: Condensed-matter physics | Optical physics | Materials physics
A molecular state of correlated electrons in a quantum dot
Sokratis Kalliakos1, Massimo Rontani2, Vittorio Pellegrini1, César Pascual García1, Aron Pinczuk3,4, Guido Goldoni2, Elisa Molinari2, Loren N. Pfeiffer4 & Ken W. West4
Correlation among particles in finite quantum systems leads to complex behaviour and novel states of matter. One remarkable example is predicted to occur in a semiconductor quantum dot1, 2, 3, where at vanishing electron density the Coulomb interaction between electrons rigidly fixes their relative positions as those of the nuclei in a molecule4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14. In this limit, the neutral few-body excitations are roto-vibrations, which have either rigid-rotor or relative-motion character15. In the weak correlation regime, on the contrary, the Coriolis force mixes rotational and vibrational motions. Here, we report evidence for roto-vibrational modes of an electron molecular state at densities for which electron localization is not yet fully achieved. We probe these collective modes by using inelastic light scattering16, 17, 18 in quantum dots containing four electrons19. Spectra of low-lying excitations associated with changes of the relative-motion wavefunction—the analogues of the vibration modes of a conventional molecule—do not depend on the rotational state represented by the total angular momentum. Theoretical simulations by the configuration-interaction method20 are in agreement with the observed roto-vibrational modes and indicate that such molecular excitations develop at the onset of short-range correlation.
- NEST INFM-CNR and Scuola Normale Superiore, 56126 Pisa, Italy
- S3 INFM-CNR and Department of Physics, University of Modena and Reggio Emilia, 41100 Modena, Italy
- Depts of Appl. Phys and Appl. Math. and of Physics, Columbia University, New York 10027, USA
- Bell Laboratories, Alcatel-Lucent, Murray Hill, New Jersey 07974, USA
Correspondence to: Massimo Rontani2 e-mail: rontani@unimore.it
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