Vertically coupled double quantum rings at zero magnetic field

TL;DR

This study uses density functional theory to analyze how the electronic states and addition spectra of double quantum rings change with inter-ring distance and coupling strength at zero magnetic field.

Contribution

It provides a detailed theoretical investigation of electron localization and spectral properties in coupled quantum rings, highlighting effects of coupling and structural mismatches.

Findings

Strong coupling leads to delocalized electronic states resembling a single ring.

Weak coupling results in localized states in individual rings.

Structural mismatches induce localization by shifting energy levels.

Abstract

Within local-spin-density functional theory, we have investigated the `dissociation' of few-electron circular vertical semiconductor double quantum ring artificial molecules at zero magnetic field as a function of inter-ring distance. In a first step, the molecules are constituted by two identical quantum rings. When the rings are quantum mechanically strongly coupled, the electronic states are substantially delocalized, and the addition energy spectra of the artificial molecule resemble those of a single quantum ring in the few-electron limit. When the rings are quantum mechanically weakly coupled, the electronic states in the molecule are substantially localized in one ring or the other, although the rings can be electrostatically coupled. The effect of a slight mismatch introduced in the molecules from nominally identical quantum wells, or from changes in the inner radius of the constituent rings, induces localization by offsetting the energy levels in the quantum rings. This plays a crucial role in the appearance of the addition spectra as a function of coupling strength particularly in the weak coupling limit.