Impurity effects in few-electron quantum dots: Incipient Wigner molecule regime

TL;DR

This study uses path-integral Monte Carlo simulations to explore how a single impurity impacts the electronic structure and spin properties of few-electron quantum dots in the incipient Wigner molecule regime, revealing significant alterations in shell filling, spin gaps, and spatial order.

Contribution

It provides the first detailed numerical analysis of impurity effects on strongly interacting electrons in quantum dots within the incipient Wigner molecule regime.

Findings

Impurity destroys standard shell-filling sequence and introduces a new peak at N=8.

Spin gaps are reduced by the impurity.

Impurity induces sub-Hund's rule spin S=0 at N=8.

Abstract

Numerically exact path-integral Monte Carlo data are presented for $N\leq 10$ strongly interacting electrons confined in a 2D parabolic quantum dot, including a defect to break rotational symmetry. Low densities are studied, where an incipient Wigner molecule forms. A single impurity is found to cause drastic effects: (1) The standard shell-filling sequence with magic numbers $N=4,6,9$, corresponding to peaks in the addition energy $\Delta(N)$, is destroyed, with a new peak at N=8, (2) spin gaps decrease, (3) for N=8, sub-Hund's rule spin S=0 is induced, and (4) spatial ordering of the electrons becomes rather sensitive to spin. We also comment on the recently observed bunching phenomenon.