Impacts of structural asymmetry on the magnetic response of excitons and biexcitons in single self-assembled In(Ga)As quantum rings

Abstract

The diamagnetic shifts of neutral excitons and biexcitons confined in single self-assembled In͑Ga͒As/GaAs quantum rings are investigated. Unlike quantum dots, quantum rings reveal a considerably large biexciton diamagnetic shift, about two times larger than that of single excitons. Based on model calculations, we found that the inherent structural asymmetry and imperfection, combined with the interparticle Coulomb interactions, is the fundamental cause of the more extended biexciton wave function in the quantum rings. The exciton wave function tends to be localized in one of the potential valleys induced by structural imperfections of the quantum ring due to the strong localization of hole and the electron-hole Coulomb attraction, resembling the behavior in single dots. Our results suggest that the phase coherence of neutral excitons in quantum rings will be smeared out by such wave function localizations.

Excited exciton and biexciton localised states in a single quantum ring

“…This may explain why some experiments failed to observe excitonic AB oscillations in a QR. 13,15 In this work, we confirm the presence of a strongly localised state in a volcano-like QR in terms of an absence of excitonic AB oscillations up to 14 T, with a small diamagnetic coefficient the polar nature and large polarisation asymmetry of biexcitons and excited excitons. These arise as a consequence of the small lateral extension and asymmetry of the strongly localised crescent-like structure in the QR.…”

“…A delocalised wavefunction around the rim is a prerequisite for the AB effect, but the presence of localised states has been reported in a volcano-like QR arising from height anisotropy, 4,13,14 whereby the phase coherence around the rim can be inhibited. The degree of localisation seems to depend upon the anisotropy; when this is negligible, 10 excitonic AB oscillations begin at low magnetic fields.…”

“…In the intermediate range of localisation, excitons are localised separately near the two highest rims in a QR, but the two excitons can be paired in a biexciton with sub-meV binding energy. 13 In the case of strong localisation in a QR, 4 no persistent current emerges unless a large magnetic field is applied. Optical AB oscillations in a QR have not been considered in the context of the localisation induced by rim height-anisotropy.…”

Quasi-one-dimensional density of states in a single quantum ring

“…When a volcano-like rim anisotropy is present1112131415, the wavefunction becomes localized with a crescent-like shape161718. Provided that the degree of localization is moderate, rotational motion of an exciton around the whole circumference can be possible through tunneling.…”

In-plane mapping of buried InGaAs quantum rings and hybridization effects on the electronic structure

“…21 but not observed in other similar structures. 24,25 Small variations of structural parameters of the QRs, such as shape, outer and/or inner radius size, height, and asymmetry, may interfere on the electronic structure. 26 Thus, understanding the effect of ring size and shape on carrier confinement and the formation of strain fields became the main objectives of our discussion.…”