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...
Interdot coupling in (In,Ga)As/GaAs quantum dot arrays is studied by means of steady state and time-resolved photoluminescence (PL). A peculiar dependence of the PL decay time on the excitation and detection energy is revealed and ascribed to the peculiarities of the carrier and energy relaxation caused by both immediate electronic interdot coupling and long-range coupling through the radiation field.
We report experimental evidence of excitonic spin-splitting, in addition to the conventional Zeeman effect, produced by a combination of the Rashba spin-orbit interaction, Stark shift and charge screening. The electric-field-induced modulation of the spin-splitting are studied during the charging and discharging processes of p-type GaAs/AlAs double barrier resonant tunneling diodes (RTD) under applied bias and magnetic field. The abrupt changes in the photoluminescence, with the applied bias, provide information of the charge accumulation effects on the device.The effect of the spin-orbit (SO) interaction in quasitwo-dimensional (Q2D) systems has attracted renewed attention in recent years. The topic has been on the focus of many optical and transport investigations of spin-related phenomena in nanoscopic systems [1,2,3], a subject of great fundamental and technological interest [4,5,6,7]. In this letter, we address experimental evidence of electric field coupling to the spin degree of freedom of carriers in RTD; here in particular, the prevailing influence can be attributed to the SO and Stark effects on the hole electronic structure. These interactions are relevant to the study of the internal electric fields and the charge accumulation in the structure. The simultaneous investigation of optical and transport properties at high magnetic and electric parallel fields, has permitted a thorough characterization of the main processes involved in the system response. The novelty of this result consists of the optical detection of electric field modulation of the effective spin-splitting beyond the Zeeman effect and its unambiguous correlation to the transport mechanisms which is responsible for the charge buildup in the states of the RTD.This study is carried out on a symmetric p − i − p GaAs/AlAs RTD, that has been previously used to characterize hole space charge buildup and resonant effects in a magnetic field [8]. The structure is in the form of a 400µm diameter mesa with a metallic AuGe annular top contact to allow optical access. The diode was mounted in a superconducting magnet and the emission spectra were recorded using a double spectrometer coupled to a CCD system with polarizer facilities to select left (right) σ +(−) configurations. When light from an Ar + laser is focused close to the surface, minority electrons are created [8]. As the bias approaches a resonant condition, the carrier density inside the QW increases and then decreases, resulting in the negative differential resistance (NDR) region when the resonance is traversed. The photo-generated electrons tunneling into the QW layer can recombine with the injected holes or tunnel out of the well layer. These processes are represented schematically in the Fig. 1 (a).The I − V characteristics, shown in Fig. 1 (b), displays a series of peaks associated with the injected holes (I dark ) from the hole accumulation layer formed in the outside interface of the diode (see Fig. 1 (a)). Under illumination, an increase of current is observed (I light ) due to ...
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