Antibonding ground states in semiconductor artificial molecules

TL;DR

This paper reports the first experimental observation of antibonding ground states in semiconductor quantum dot molecules, revealing a counterintuitive change in molecular orbital character driven by spin-orbit interaction.

Contribution

It demonstrates the existence of antibonding molecular ground states in artificial semiconductor molecules, a phenomenon not seen in natural diatomic molecules, using magneto-optical spectroscopy and theoretical modeling.

Findings

Observation of antibonding ground states in coupled quantum dots

Reversal of molecular ground state character with barrier thickness

Validation of results with a four-band k.p model including strain effects

Abstract

The spin-orbit interaction is a crucial element of many semiconductor spintronic technologies. Here we report the first experimental observation, by magneto-optical spectroscopy, of a remarkable consequence of the spin-orbit interaction for holes confined in the molecular states of coupled quantum dots. As the thickness of the barrier separating two coupled quantum dots is increased, the molecular ground state changes character from a bonding orbital to an antibonding orbital. This result is counterintuitive, and antibonding molecular ground states are never observed in natural diatomic molecules. We explain the origin of the reversal using a four band k.p model that has been validated by numerical calculations that account for strain. The discovery of antibonding molecular ground states provides new opportunities for the design of artificially structured materials with complex molecular properties that cannot be achieved in natural systems.