Electronic structure of ellipsoidally deformed quantum dots

Using a three-dimensional local spin-density functional method, we investigate the electronic structure of quasi two-dimensional ellipsoidal quantum dots with elliptical deformation. Changes in the electron addition energy spectra and spin polarization are investigated as a function of the number of electrons and the elliptical deformation on the lateral direction confinement potential, and compared with those of a circular dot which shows a shell structure. Especially, we find that, due to the electron–electron interaction, the anisotropy of an elliptical dot is higher than that of a bare potential by ∼ 1.2 for experimentally realistic potentials. The identification and understanding of the electronic structure of quantum dots is currently a major interest of the nanotechnology community [1,2]. In particular, single electron addition techniques together with the realization of clean and highly symmetric vertical quantum dots [3] offer the possibility to manipulate and study dots with a small well-defined adjustable number of electrons. A quasi two-dimensional (2D) shell structure, such as the enhancement of electron addition energies for certain number of electrons and spin-state variations according to Hund’s first rule, is clearly observed in circular dots [3]. This experimental identification of the shell structure is also in good agreement with theoretical model calculations [4–7]. While the full rotational symmetry of a circular dot leads to the most prominent shell structure and well-defined physical pictures, there has also been other recent experimental [8] and theoretical [4,7,8] efforts to identify the role of the interplay between the circular symmetry breaking in the external potentials and the electron–electron interaction on the electronic structure of quantum dots. The finite electron addition spectra in quantum dots are closely related to the physics of single electron transistor applications, and the manipulation of the electron-spin states is also an interesting subject in magnetoelectric and optoelectric applications [2,9]. Since the presence of the asymmetry in the confining potential should be experimentally more realistic, it is important to understand the role of the symmetry breaking on the electronic structure of quantum dots due to such as an impurity [10] or the potential deformation. 0953-8984/01/091987+07$30.00 © 2001 IOP Publishing Ltd Printed in the UK 1987