Ellipsoidal deformation of vertical quantum dots

TL;DR

This study investigates how elliptical deformation affects the electronic shell structure and spin states of vertical quantum dots, revealing significant modifications and a predicted spin transition in four-electron systems.

Contribution

It provides the first detailed analysis of how ellipsoidal deformation alters the addition energy spectra and spin configurations of quantum dots, supported by model calculations and experimental data.

Findings

Deformation radically alters shell structure and addition energies.

Elliptical deformation induces 'piezo-magnetic' behavior.

Predicted spin-triplet to singlet transition at four electrons.

Abstract

Addition energy spectra at 0 T of circular and ellipsoidally deformed few-electron vertical quantum dots are measured and compared to results of model calculations within spin-density functional theory. Because of the rotational symmetry of the lateral harmonic confining potential, circular dots show a pronounced shell structure. With the lifting of the single- particle level degeneracies, even a small deformation is found to radically alter the shell structure leading to significant modifications in the addition energy spectra. Breaking the circular symmetry with deformation also induces changes in the total spin. This "piezo-magnetic" behavior of quantum dots is discussed, and the addition energies for a set of realistic deformation parameters are provided. For the case of the four-electron ground state at 0 T, a spin-triplet to spin-singlet transition is predicted, i.e. Hund's first rule no longer applies. Application of a magnetic field parallel to the current confirms that this is the case, and also suggests that the anisotropy of an elliptical dot, in practice, may be higher than that suggested by the geometry of the device mesa in which the dot is located.