Vertically coupled double quantum dots in magnetic fields

TL;DR

This paper investigates the ground and excited states of vertically coupled double quantum dots under magnetic fields, revealing how electron correlations and tunneling influence their properties and optical spectra, with implications for spin blockade phenomena.

Contribution

It provides a comprehensive analysis of electron correlations, spin effects, and optical properties in double quantum dots, including the impact of Landau level mixing and the connection between spin and angular momentum.

Findings

Magic numbers reflect a crossover between intra- and inter-layer electron correlations.

The position of the crossover depends on tunneling strength and magnetic field.

Spin blockade can occur due to spin selection rules, more easily in double dots.

Abstract

Ground-state and excited-state properties of vertically coupled double quantum dots are studied by exact diagonalization. Magic-number total angular momenta that minimize the total energy are found to reflect a crossover between electron configurations dominated by intra-layer correlation and ones dominated by inter-layer correlation. The position of the crossover is governed by the strength of the inter-layer electron tunneling and magnetic field. The magic numbers should have an observable effect on the far infra-red optical absorption spectrum, since Kohn's theorem does not hold when the confinement potential is different for two dots. This is indeed confirmed here from a numerical calculation that includes Landau level mixing. Our results take full account of the effect of spin degrees of freedom. A key feature is that the total spin, $S$, of the system and the magic-number angular momentum are intimately linked because of strong electron correlation. Thus $S$ jumps hand in hand with the total angular momentum as the magnetic field is varied. One important consequence of this is that the spin blockade (an inhibition of single-electron tunneling) should occur in some magnetic field regions because of a spin selection rule. Owing to the flexibility arising from the presence of both intra-layer and inter-layer correlations, the spin blockade is easier to realize in double dots than in single dots.