A molecular state of correlated electrons in a quantum dot

• Published in: Nature physics Vol. 4; no. 6; pp. 467 - 471
• Main Authors: Rontani, Massimo, Pellegrini, Vittorio, Kalliakos, Sokratis, García, César Pascual, Pinczuk, Aron, Goldoni, Guido, Molinari, Elisa, Pfeiffer, Loren N, West, Ken W
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2008; Nature Publishing Group
• Subjects: Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Coriolis force; Electrons; letter; Light scattering; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Quantum dots; Semiconductors; Simulation; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys944

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 dot, where at vanishing electron density the Coulomb interaction between electrons rigidly fixes their relative positions as those of the nuclei in a molecule. In this limit, the neutral few-body excitations are roto-vibrations, which have either rigid-rotor or relative-motion character. 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 scattering in quantum dots containing four electrons. 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 method are in agreement with the observed roto-vibrational modes and indicate that such molecular excitations develop at the onset of short-range correlation.