Mechanism of non-classical light emission from acoustically populated (311)A GaAs quantum wires

We employ surface acoustic waves (SAWs) to control the transfer of photo-generated carriers between interconnected quantum wells and quantum wires (QWRs) grown on pre-patterned (311)A GaAs substrates. Optical studies, carried out under remote acoustic excitation of a single QWR, have shown sharp photoluminescence lines and antibunched photons with tunable emission energy. These features are attributed to recombination of acoustically transported carriers in potential inhomogeneities within the wire. The origin of the photon antibunching is discussed in terms of a 'bottleneck' in the number of carriers trapped in the QWR, which restricts the number of recombination events per SAW cycle. We propose a model for antibunching based on the trapping of carriers induced by the SAW piezoelectric field in states at the interface between the GaAs QWR and the AlGaAs barriers. Non-classical light is emitted during the subsequent release of the trapped carriers into the recombination centers within the wire. The spatial distribution of the emitting recombination centers is estimated using time-resolved measurements

DEEP: a provenance-aware executable document system

The concept of executable documents is attracting growing interest from both academics and publishers since it is a promising technology for the dissemination of scientific results. Provenance is a kind of metadata that provides a rich description of the derivation history of data products starting from their original sources. It has been used in many different e-Science domains and has shown great potential in enabling reproducibility of scientific results. However, while both executable documents and provenance are aimed at enhancing the dissemination of scientific results, little has been done to explore the integration of both techniques. In this paper, we introduce the design and development of DEEP, an executable document environment that generates scientific results dynamically and interactively, and also records the provenance for these results in the document. In this system, provenance is exposed to users via an interface that provides them with an alternative way of navigating the executable document. In addition, we make use of the provenance to offer a document rollback facility to users and help to manage the system's dynamic resources

Acoustic carrier transport in InP-based structures

We demonstrate the ambipolar acoustic transport of optically generated electrons and holes by surface acoustic waves in InGaAsP waveguide structures grown on InP substrates. Transport is detected by monitoring the photoluminescence in the 1400{1500-nm wavelength range emitted by the recombination of the acoustically transported carriers several hundreds of micrometers away from the photoexcitation spot

Active photonic crystals based on surface acoustic waves

An active photonic crystal (PC) based on the modulation of a one-dimensional cavity resonator by electrically-generated surface acoustic waves is described. The high nonthermal population of surface modes combined with the enhanced Brillouin scattering in the cavity increases the intensity of the scattered light to values comparable to the excitation intensity. This process is employed to switch and modulate light beams in PCs

Compact Mach-Zehnder acousto-optic modulator

The authors demonstrate a compact optical waveguidemodulator based on a Mach-Zehnder interferometer driven by surface acoustic waves. The modulator was monolithically fabricated on GaAs with an active region length of approximately 15μm. It yields peak-to-peak modulation exceeding 90% of the average transmission and operation in the gigahertz frequency range

Acoustic manipulation of electron-hole pairs in GaAs at room temperature

We demonstrate the optically detected long-range (>100 µm) ambipolar transport of photogenerated electrons and holes at room temperature by surface acoustic waves (SAWs) in (In,Ga)As-based quantum well structures coupled to an optical microcavity. We also show the control of the propagation direction of the carriers by a switch composed of orthogonal SAWbeams, which can be used as a basic control gate for information processing based on ambipolar transport

Embedded interdigital transducers for high frequency surface acoustic waves on GaAs

We investigate high-performance, high-frequency interdigital transducers (IDTs) for the generation of surface acoustic waves(SAWs) on GaAs substrates, where the metal fingers are embedded in the substrate. We demonstrate that the acoustic reflections and the scattering of the surface modes into the substrate become considerably reduced in these transducers, leading to an increased output power. The finger embedding process is particularly relevant for the generation of powerful beams of high-frequency SAWs on weak piezoelectric substrates (such as most of the semiconducting materials) using long IDTs. We also show that the reflection reduction is important for the design of focusing single-finger IDTs, since it minimizes the effects of the finger grating on the angular dependence of the phase velocit

Tunable coupled surface acoustic cavities

We demonstrate the electric tuning of the acoustic field in acoustic microcavities(MCs) defined by a periodic arrangement of metal stripes within a surface acoustic delay line on LiNbO3 substrate. Interferometric measurements show the enhancement of the acoustic field distribution within a single MC, the presence of a"bonding" and"anti-bonding" modes for two strongly coupled MCs, as well as the positive dispersion of the"mini-bands" formed by five coupled MCs. The frequency and amplitude of the resonances can be controlled by the potential applied to the metal stripes

Phonon-Induced Quantum Magnetic Deflagration in Mn12

A comprehensive set of experiments on the effect of high-frequency surface acoustic waves, SAWs, in the spin relaxation in Mn12-acetate is presented. We have studied the quantum magnetic deflagration induced by SAWs under various experimental conditions extending the data shown in a very recent paper [A. Hernandez-Minguez et. al., Phys. Rev. Lett. 95, 217205 (2005)]. We have focused our study on the dependence of both the ignition time and the propagation speed of the magnetic avalanches on the frequency, amplitude, and duration of the SAW pulses in experiments performed under different temperatures and external magnetic fields.Comment: 7 pages, 9 figure

Structure Of Interfaces In A-si

We present experimental results on the atomic structure of the interfaces between a-Si:H and a-SiNx:H layers obtained by analyzing the intensity of the Raman lines from zone-folded acoustic phonons and of the peaks of x-ray diffraction at grazing angles. We determine the width of these interfaces and their stability under thermal annealing in temperatures below the crystallization temperature.69277878