A molecular state of correlated electrons in a quantum dot

TL;DR

This paper presents experimental and theoretical evidence of roto-vibrational modes in a four-electron quantum dot, revealing the emergence of molecular-like correlated electron states at intermediate densities.

Contribution

It demonstrates the observation of electron molecular states with roto-vibrational modes in quantum dots, bridging the gap between weak and strong correlation regimes.

Findings

Observation of roto-vibrational modes via inelastic light scattering

Theoretical CI simulations confirm experimental results

Molecular excitations develop at the onset of short-range correlation

Abstract

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 (QD) where at vanishing density the Coulomb correlation among electrons rigidly fixes their relative position as that 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 of 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 inelastic light scattering in QDs containing four electrons. Spectra of low-lying excitations associated to changes of the relative-motion wave function -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 via the configuration-interaction (CI) method are in agreement with the observed roto-vibrational modes and indicate that such molecular excitations develop at the onset of short-range correlation.