Aharonov-Bohm Interference in Neutral Excitons: Effects of Built-In Electric Fields

Abstract

We report a comprehensive discussion of quantum interference effects due to the finite structure of excitons in quantum rings and their first experimental corroboration observed in the optical recombinations. Anomalous features that appear in the experiments are analyzed according to theoretical models that describe the modulation of the interference pattern by temperature and built-in electric fields.PACS numbers: 71.35.Ji, 73.21.La, 78.20.Ls, 78.67.Hc The nanoscale ring structures, or quantum rings (QRs), have attracted the interest of the scientific community due to their unique rotational symmetry and the possibility to verify quantum mechanical phenomena.[1, 2, 3] Among these, the study of Aharonov-Bohm (AB)-like effects has gained a significant impetus, [4,5,6] and these efforts have gone beyond the original discussion of the AB interpretation on the nature of electromagnetic potentials and their role in quantum mechanics. [7] It is reasonable to say that the study of coherent interference occurring in transport properties of nanoscopic QRs, as proposed in Ref. 7 encounters, at the moment, serious scale limitations which has encouraged the search for optical implications associated to AB-effects.These endeavors applied to nanoscopic QRs do not strictly meet the original conditions for the ABconfiguration since the carriers are confined within regions with finite values of magnetic field. However, we still consider an observed effect as of AB-type if it can be explained assuming that the magnetic field is ideally concentrated in the middle of the QRs, i. e., when such effect comes essentially from potential vector-mediated quantum interference. As also considered in Ref. 8, in stationary systems this interference is generally reflected in a boundary condition and it is not as explicit as in the famous picture of an AB scattering situation.In this work we consider AB-interference in excitonic states as proposed theoretically in Refs. 9, 10, 12. Instead of looking only at the oscillatory dependence on magnetic flux of the electron-hole (e − h) recombination energy during photo-luminescence (PL), we also consider the excitonic oscillator strength whose oscillatory behavior reflects directly the changes in the exciton wavefunction as the magnetic flux increases. A similar experimental work was reported in Ref. 6 for type-II QRs, however, here we study type-I systems where both electron and hole move in the ring so that the correlation between them is crucial to the oscillatory behavior found in the PL integrated intensity. The samples studied here were grown using a RIBER 32P solid-source molecular beam epitaxy chamber and the QRs were grown using the following procedure. A 0.5 µm GaAs buffer layer was grown on semi-insulating (100) GaAs substrates at 580• C, after oxide desorption. Then, it was followed by 2.2 ML of InAs and the formation of quantum dots (QDs) at 520• C. The dots were obtained using the Stranski-Krastanov growth mode. Cycles of 0.14 ML of InAs plus a 2 s interruption under As 2 flux were r...

Electric and magnetic field effects on the excitonic properties of elliptic core–multishell quantum wires

“…On the other hand, the observation of excitonic AB oscillations have been reported in semiconductor quantum rings when electrons and holes have an intrinsic spatial separation, due to built-in electric fields or structural effects. [18,19,20,21,22] In fact, our results demonstrate that in elliptic CMS wires, electrons and holes are pushed to the regions of higher curvature of the confining shell with different strengths, yielding regions of non-neutral charge and, consequently, to an enhancement of the magnetic field effect on the exciton binding energy, which starts to exhibit AB oscillations. The regions of non-neutral charge demonstrated in this paper may also play a role in other geometries of core-shell quantum wires which share the property of exhibiting high curvature regions, such as the semiconductor quantum wires with square, hexagonal and triangular cross sections reported in the literature.…”

Excitonic Aharonov-Bohm effect in a two-dimensional quantum ring

“…Our results are in good agreement with recent experimental observations where the magnitude of the excitonic AB oscillations was observed to be about 0.5 meV at binding energies of 4.35 mV for rings of about 11-22 nm radius and γ ≈ 1. 5 We also note that our confining potential (2) has been chosen to retain its nonsimple connectedness due to the infinitely repulsive centrifugal core at the center. Hence even for very wide rings, there is an essential difference with respect to the previously considered 2D confining potentials.…”

“…29,30 In all cases, the excitonic AB effect for neutral excitons has been argued to be suppressed in 2D as the width of the ring is increased. 31 Recently, experimental results in molecularbeam-epitaxy grown nanorings made by AsBr 3 8 etching and on self-assembled InAs/GaAs quantum dots 5 report oscillations in the binding energy of neutral excitons that may be accounted for by the excitonic AB effect.…”

“…Recent advances in nanofabrication of quantum rings and dots by self-assembling, [1][2][3][4][5] lithographic, 6,7 or etching techniques 8 have opened an active area of research both theoretical and experimental. In such systems, electrons and holes are confined in a small region and consequently the Coulomb interaction is enhanced.…”

Structural and magnetic confinement of holes in the spin-polarized emission of coupled quantum ring–quantum dot chains

“…It has been predicted [13] that the in-plane radial polarization of excitons in finite-width QRs can produce a strong modulation of the oscillator strength of the excitonic transition with magnetic field, due to a topologically determined quantum interference known as the Aharonov-Bohm (AB) effect [13][14][15][16][17]. The AB interference in type-I systems, where both electron and hole move together inside the ring, has been found in the magneto-PL (photoluminescence) from self-assembled InGaAs/GaAs QR single layer structures [16].…”