Optical exciton Aharonov-Bohm effect, persistent current, and magnetization in semiconductor nanorings of type I and II

Abstract

The optical exciton Aharonov-Bohm effect, i. e. an oscillatory component in the energy of optically active (bright) states, is investigated in nanorings. It is shown that a small effective electron mass, strong confinement of the electron, and high barrier for the hole, achieved e. g. by an InAs nanoring embedded in an AlGaSb quantum well, are favorable for observing the optical exciton Aharonov-Bohm effect. The second derivative of the exciton energy with respect to the magnetic field is utilized to extract Aharonov-Bohm oscillations even for the lowest bright state unambiguously. A connection between the theories for infinitesimal narrow and finite width rings is established. Furthermore, the magnetization is compared to the persistent current, which oscillates periodically with the magnetic field and confirms thus the non-trivial (connected) topology of the wave function in the nanoring.

Gate controlled Aharonov-Bohm-type oscillations from single neutral excitons in quantum rings

“…In order to observe the oscillation clearly, we give the results of the second derivative of the exciton total energy with respect to the magnetic field. 7 The minima of this quantity corresponds to changes in the ground state, e.g., the transition points at ϳ2.6 and ϳ8 T in Fig. 5͑b͒.…”

“…Theoretical investigations have predicted that in semiconductor quantum rings with a confined exciton, the AB effect can be probed from the photoluminescence ͑PL͒ emission since the change in the phase of the wave function is accompanied by a change in the exciton total angular momentum, making the PL emission magnetic field dependent. 6,7,[10][11][12][13] Bayer et al 14 reported this effect for a charged exciton confined in a lithography defined QR. PL emission from indirect excitons in stacked ZnTe/ZnSe ensemble quantum dots ͑QDs͒ shows similar oscillations, 15,16 this behavior was explained by the type-II band alignment which confines one carrier inside the QD and the other carrier in the barrier, mimicking a QR-like structure.…”

“…[3][4][5] For an electron-hole pair ͑i.e., a neutral exciton͒ confined in specially designed nanostructures, the phases accumulated by the two species will be generally different after one revolution, leading to modulations between different quantum states. 6,7 Recent experimental works on the AB effect in ringlike semiconductor structures include magnetotransport measurements on a single-quantum ring ͑QR͒ fabricated by local oxidation with atomic force microscope ͑AFM͒, 5 far-infrared spectroscopy, 8 and magnetization spectroscopy 9 on selfassembled InGaAs nanorings epitaxially grown by StranskiKrastanow ͑SK͒ mode. Theoretical investigations have predicted that in semiconductor quantum rings with a confined exciton, the AB effect can be probed from the photoluminescence ͑PL͒ emission since the change in the phase of the wave function is accompanied by a change in the exciton total angular momentum, making the PL emission magnetic field dependent.…”

Aharonov-Bohm Excitons at Elevated Temperatures in Type-IIZnTe/ZnSeQuantum Dots

“…The AB effect is a property of charged particles and, in a naive picture, neutral excitons would not exhibit AB oscillations. Nevertheless, there have been several theoretical predictions [9][10][11][12] concerning a mechanism leading to AB oscillations for neutral composite quasi-particles. This is due to the fact that electron and hole in a ring-like nanostructure may move over different trajectories resulting in a non-zero electric dipole moment and, therefore, to measurable AB effects.…”

“…This is due to the fact that electron and hole in a ring-like nanostructure may move over different trajectories resulting in a non-zero electric dipole moment and, therefore, to measurable AB effects. Type-II quantum dots (QDs) have been predicted to be particularly amenable to exhibiting such AB effects because of enhanced polarization of the composite particle due to the spatial separation of the electron and hole in such systems [9][10][11][12].…”