From Dot to Ring: Tunable Exciton Topology in Type-II InAs/GaAsSb Quantum Dots

Abstract

We present an experimental and theoretical study about the carrier confinement geometry and topology in InAs/GaAsSb quantum dots. The investigated sample consists of a field-effect device embedding a single layer of dot-in-a-well InAs/GaAsSb nanostructures. These nanostructures exhibit large electron-hole dipole moments and radiative lifetimes under externally applied electric fields. Both phenomena are related to the type-II band alignment existing between the two materials which, in principle, could also result in a change of the hole orbital confinement topology from simply to doubly connected. The latter aspect will be confirmed by ensemble magnetophotoluminescence experiments at 4.2 K. The oscillations observed in the photoluminescence intensity and degree of circular polarization will be described by an axially symmetric k· p model combining vertical electric and magnetic fields. Due to the large spin-orbit coupling of III-Sb nanostructures, the modulation of the orbital confinement geometry and topology reported here shall open a venue to control the spin dynamics by external voltages. This exciting idea will be theoretically discussed through band-effective models including spin-orbit coupling and anisotropic confinement effects.