We report a comprehensive discussion of quantum interference effects due to the finite structure of neutral excitons in quantum rings and their first experimental corroboration observed in the ...optical recombinations. The signatures of built-in electric fields and temperature on quantum interference are demonstrated by theoretical models that describe the modulation of the interference pattern and confirmed by complementary experimental procedures.
Although extensive research on nanostructures has led to the discovery of a number of efficient ways to confine carriers in reduced dimensions, little has been done to make use of the unique ...properties of various nanostructured systems through coupling by means of the controllable transfer of carriers between them. Here, we demonstrate a novel approach for the controllable transfer of electrons and holes between a semiconductor quantum well and an embedded quantum dot using the moving piezoelectric potential modulation induced by an acoustic phonon. We show that this moving potential not only transfers carriers between the quantum well and an array of quantum dots, but can also control their capture and recombination in discrete quantum dot states within the array. This feature is used to demonstrate a high-frequency, single-photon source with tunable emission energy by acoustically transferring carriers to a selected quantum dot.
Time-resolved Kerr rotation measurements were performed in InGaAs/GaAs quantum wells nearby a doped Mn delta layer. Our magneto-optical results show a typical time evolution of the optically-oriented ...electron spin in the quantum well. Surprisingly, this is strongly affected by the Mn spins, resulting in an increase of the spin precession frequency in time. This increase is attributed to the variation in the effective magnetic field induced by the dynamical relaxation of the Mn spins. Two processes are observed during electron spin precession: a quasi-instantaneous alignment of the Mn spins with photo-excited holes, followed by a slow alignment of Mn spins with the external transverse magnetic field. The first process leads to an equilibrium state imprinted in the initial precession frequency, which depends on pump power, while the second process promotes a linear frequency increase, with acceleration depending on temperature and external magnetic field. This observation yields new information about exchange process dynamics and on the possibility of constructing spin memories, which can rapidly respond to light while retaining information for a longer period.
Mobile piezoelectric potentials are used to coherently transport electron spins in GaAs (110) quantum wells (QW) over distances exceeding 60 microm. We demonstrate that the dynamics of mobile spins ...under external magnetic fields depends on the direction of motion in the QW plane. This transport anisotropy is an intrinsic property of moving spins associated with the bulk inversion asymmetry of the underlying GaAs lattice.
We investigated the dynamics of the interaction between spin-polarized photo-created carriers and Mn ions on InGaAs/GaAs: Mn structures. The carriers are confined in an InGaAs quantum well and the Mn ...ions come from a Mn delta-layer grown at the GaAs barrier close to the well. Even though the carriers and the Mn ions are spatially separated, the interaction between them is demonstrated by time-resolved spin-polarized photoluminescence measurements. Using a pre-pulse laser excitation with an opposite circular-polarization clearly reduces the polarization degree of the quantum-well emission for samples where a strong magnetic interaction is observed. The results demonstrate that the Mn ions act as a spin-memory that can be optically controlled by the polarization of the photocreated carriers. On the other hand, the spin-polarized Mn ions also affect the spin-polarization of the subsequently created carriers as observed by their spin relaxation time. These effects fade away with increasing time delays between the pulses as well as with increasing temperatures.
The results of studies of the time-resolved photoluminescence in semiconductor heterostructures containing two noninteracting InGaAs quantum wells in a GaAs matrix are reported. One of the quantum ...wells was undoped, and the other was uniformly doped with chromium atoms (InGaAs:Cr). It was shown that the introduction of Cr had a profound effect on the recombination lifetime of charge carriers in quantum wells. The change in the photoluminescence intensity after excitation cannot be described by a monoexponential decay function, which is attributed to a change in the built-in electric field of the surface barrier in the quantum wells because of screening by photoexcited charge carriers.
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