Spontaneous emission of quantum dot systems in laterally structured microcavities that exhibit photon confinement in all three directions has been studied by time-resolved photoluminescence spectroscopy. For on-resonance conditions, we find that the dot emission rate is increased substantially over that of the unstructured planar cavity. For off-resonance conditions, we are able to suppress the emission rate by an order of magnitude by using cavities with metal coatings, which we attribute to the suppression of leaky optical modes in these structures.
Electron spin dynamics is investigated in n-i-n GaAs/AlGaAs coupled quantum wells. The electron spin dephasing time is measured as a function of an external electrical bias under resonant excitation of the 1sHH intrawell exciton using a time-resolved Kerr rotation technique. It is found a strong electron spin dephasing time anisotropy caused by an interference of the structure inversion asymmetry and the bulk inversion asymmetry. This anisotropy is shown to be controlled by an electrical bias. A theoretical analysis of electron spin dephasing time anisotropy is developed. The ratio of Rashba and Dresselhaus spin splittings is studied as a function of applied bias.Introduction. Critical point of spintronic investigations is a control of spin degrees of freedom by electrical means. There are proposals to create electronic devices working due to an electric field effect on the orientation of electron spins. In order to study such phenomena one needs to use a coupling between orbital and spin degrees of freedom. This is possible due to spin-orbit interaction, an universal relativistic effect which, however, can be altered in semiconductors and low-dimensional semiconductor systems by special structure design and/or external parameters. Especially interesting for both fundamental physics and applications is the spin-orbit interaction caused by lack of inversion center in the system. The important example is a class of effects caused by Structure Inversion Asymmetry (SIA) which is present in two-dimensional semiconductor structures. 1 There is a number of works where the SIA degree has been changed in two-dimensional structures by an external gate. 2,3 However in most cases the effect of the gate voltage is a change of the electron gas concentration, which produces an additional internal electric field affecting SIA. Among the quasi-two-dimensional objects based on semiconductor heterostructures, Coupled Quantum Wells (CQWs) are of special interest. Electrical bias in such structures does not produce extra carriers but has dramatic effects on SIA. This allows for direct manipulation by spin-orbit interaction even in undoped structures. In addition, CQWs are very suitable objects for spin dynamics study because, due to spatial separation of photoexcited electrons and holes in neighboring quantum wells, the radiative lifetimes are long enough so that the spin lifetime is determined by spin relaxation processes.SIA manifests itself as a source of spin relaxation of free electrons in two-dimensional semiconductors. It generates an effective magnetic field rotating electron spins which is the basis of the D'yakonov-Perel' spin relaxation mechanism, for review see Ref. 4. Accordingly, the spin relaxation times measurements give the necessary information about the degree of SIA. In addition to SIA, there is another source for lacking inversion symmetry in semiconductors. This is Bulk Inversion Asymmetry (BIA) present in structures based on noncentrosymmetric materials and also leading to the D'yakonov-Perel' spin re-
Experimental and theoretical studies of the coherent spin dynamics of two-dimensional GaAs/AlGaAs electron gas were performed. The system in the quantum Hall ferromagnet state exhibits a spin relaxation mechanism that is determined by many-particle Coulomb interactions. In addition to the spin exciton with changes in the spin quantum numbers of δS = δSz = −1, the quantum Hall ferromagnet supports a Goldstone spin exciton that changes the spin quantum numbers to δS = 0 and δSz = −1, which corresponds to a coherent spin rotation of the entire electron system to a certain angle. The Goldstone spin exciton decays through a specific relaxation mechanism that is unlike any other collective spin state. PACS numbers: 73.43. Lp,71.70.Di,75.30.Ds Introduction. Spin relaxation mechanisms in twodimensional (2D) electron systems have not yet been elucidated due to the large number of competing mechanisms and the complex effects of the manyparticle Coulomb interactions on relaxation. 2D confinement and the quantizing magnetic field ensure a cardinal rearrangement of the electron energy spectrum, effectively making it zero-dimensional. Standard single-particle relaxation channels (see, e.g., Ref.[1] and the references therein) are suppressed, which prolongs spin relaxation time. On the other hand, electron-electron correlations, very essential in the case, make the spectrum again two-dimensional. At integer filling factors and at some fractional ones the simplest electron excitations are magnetoexcitons [2] with well defined 2D momenta, specifically representing magnetoplasmons, spin waves, or spin-cyclotron excitons [3][4][5][6][7][8]. New spin relaxation mechanisms, e.g., related to the exciton-exciton scattering processes appear.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.