Magnetically controlled exciton transfer in hybrid quantum dot-quantum well nanostructures

A magnetophotoluminescence study of the carrier transfer with hybrid InAs/GaAs quantum dot(QD)-InGaAs quantum well (QW) structures is carried out where we observe an unsual dependence of the photoluminescence (PL) on the GaAs barrier thickness at strong magnetic field and excitation density. For the case of a thin barrier the QW PL intensity is observed to increase at the expense of a decrease in the QD PL intensity. This is attributed to changes in the interplane carrier dynamics in the QW and the wetting layer (WL) resulting from increasing the magnetic field along with changes in the coupling between QD excited states and exciton states in the QW and the WL

Pathway to an excitonic coherence

This paper discusses the combined effects of optical excitation power, interface roughness, lattice temperature, and applied magnetic fields on the spin-coherence of excitonic states in GaAs/AlGaAs multiple quantum wells. For low optical powers, at lattice temperatures between 4 K and 50 K, the scattering with acoustic phonons and short-range interactions appear as the main decoherence mechanisms. Statistical fluctuations of the band-gap however become also relevant in this regime and we were able to deconvolute them from the decoherence contributions. The circularly polarized magneto-photoluminescence unveils a non-monotonic tuning of the coherence for one of the spin components at low magnetic fields. This effect has been ascribed to the competition between short-range interactions and spin-flip scattering, modulated by the momentum relaxation time

Pinning of spiral fluxons by giant screw dislocations in YBa_2Cu_3O_7 single crystals: Josephson analog of the fishtail effect

By using a highly sensitive homemade AC magnetic susceptibility technique, the magnetic flux penetration has been measured in YBa_2Cu_3O_7 single crystals with giant screw dislocations (having the structure of the Archimedean spirals) exhibiting a=3 spiral turnings, the pitch b=18.7 microns and the step height c=1.2nm (the last parameter is responsible for creation of extended weak-link structure around the giant defects). The magnetic field applied parallel to the surface enters winding around the weak-link regions of the screw in the form of the so-called spiral Josephson fluxons characterized by the temperature dependent pitch b_f(T). For a given temperature, a stabilization of the fluxon structure occurs when b_f(T) matches b (meaning an optimal pinning by the screw dislocations) and manifests itself as a pronounced low-field peak in the dependence of the susceptibility on magnetic field (applied normally to the surface) in the form resembling the high-field (Abrikosov) fishtail effect.Comment: see also http://www.jetpletters.ac.ru/ps/1886/article_28701.shtm

A novel subwavelength plasmon-polariton optical filter based on tilted coupled structures

This work proposes a completely new approach for the design of resonant structures aiming at wavelength-filtering applications. The structure consists of a subwavelength metal-insulator-metal (MIM) waveguide presenting tilted coupled structures transversely arranged in the midpoint between the input and output ports. The cavity-like response of this device has shown that this concept can be particularly attractive for optical filter design for telecom applications. The extra degree of freedom provided by the tilting of the cavity has proved to be not only very effective on improving the quality factor of these structures, but also to be an elegant way of extending the range of applications for tuning multiple wavelengths, if necessary.FAPESPCNP

Collective plasmon-modes in gain media: quantum emitters and plasmonic nanostructures

This book represents the first detailed description, including both theoretical aspects and experimental methods, of the interaction of rare-earth ions with surface plasmon polariton from the point of view of collective plasmon-photon interactions via resonance modes (metal nanoparticles or nanostructure arrays) with quantum emitters (rare-earth ions). These interactions are of particular interest for applications to optical telecommunications, optical displays, and laser solid state technologies. Thus, our main goal is to give a more precise overview of the rapidly emerging field of nanophotonics by means of the study of the quantum properties of light interaction with matter at the nanoscale. In this way, collective plasmon-modes in a gain medium result from the interaction/coupling between a quantum emitter (created by rare-earth ions) with a metallic surface, inducing different effects such as the polarization of the metal electrons (so-called surface plasmon polariton - SPP), a field enhancement sustained by resonance coupling, or transfer of energy due to non-resonant coupling between the metallic nanostructure and the optically active surrounding medium. These effects counteract the absorption losses in the metal to enhance luminescence properties or even to control the polarization and phase of quantum emitters. The engineering of plasmons/SPP in gain media constitutes a new field in nanophotonics science with a tremendous technological potential in integrated optics/photonics at the nanoscale based on the control of quantum effects. This book will be an essential tool for scientists, engineers, and graduate and undergraduate students interested not only in a new frontier of fundamental physics, but also in the realization of nanophotonic devices for optical telecommunication