EFFECT OF ELECTRON-ELECTRON INTERACTIONS IN A QUANTUM-DOT WITH A TAPERED CONSTRICTION

We study the effect of electron-electron interactions between several electrons in a quantum dot with a tapered constriction by monitoring t he behavior of the position of the absolute charge density maximum, Z( max), of each occupied st;lte under DC electric fields. States of this system are localized in, and can be identified with, either the left- or right-hand region, separated by the neck of the constriction. To de monstrate the effect, two cases with three electrons in the quantum do t were studied: (i) One electron is in the left-hand side region and t he other two electrons are in the right-hand side region. They occupy the two lowest energy states of the quantum dot system. The movement o f the Z(max) of the singly occupied state through the constriction doe s not show any unusual behavior except that it can be accelerated by a resonance process. (2) All three electrons are in the left-hand side region and occupy the two lowest energy states in that region. In this case, the Z(max)'s of the two states move through the constriction in a competitive manner which would not be anticipated on the basis of e ither energy considerations or the results of case 1. Furthermore, and most significantly, we show that this unusual behavior depends comple tely upon electron-electron interactions: if they are not taken into a ccount, it does not occur. We show also that this competitive process can occur in a ground-state configuration. (C) 1997 Academic Press Lim ited.