16,932 research outputs found

    Microwave-induced resistance oscillations in a back-gated GaAs quantum well

    Full text link
    We performed effective mass measurements employing microwave-induced resistance oscillation in a tunable-density GaAs/AlGaAs quantum well. Our main result is a clear observation of an effective mass increase with decreasing density, in general agreement with earlier studies which investigated the density dependence of the effective mass employing Shubnikov- de Haas oscillations. This finding provides further evidence that microwave-induced resistance oscillations are sensitive to electron-electron interactions and offer a convenient and accurate way to obtain the effective mass.Comment: 4 pages, 4 figure

    Lattice QCD calculation of ππ\pi\pi scattering length

    Full text link
    We study s-wave pion-pion (ππ\pi\pi) scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV. In the "Asqtad" improved staggered fermion formulation, we calculate the ππ\pi\pi four-point functions for isospin I=0 and 2 channels, and use chiral perturbation theory at next-to-leading order to extrapolate our simulation results. Extrapolating to the physical pion mass gives the scattering lengths as mπa0I=2=−0.0416(2)m_\pi a_0^{I=2} = -0.0416(2) and mπa0I=0=0.186(2)m_\pi a_0^{I=0} = 0.186(2) for isospin I=2 and 0 channels, respectively. Our lattice simulation for ππ\pi\pi scattering length in the I=0 channel is an exploratory study, where we include the disconnected contribution, and our preliminary result is near to its experimental value. These simulations are performed with MILC 2+1 flavor gauge configurations at lattice spacing a≈0.15a \approx 0.15 fm.Comment: Remove some typo

    Two-component model for the chemical evolution of the Galactic disk

    Get PDF
    In the present paper, we introduce a two-component model of the Galactic disk to investigate its chemical evolution. The formation of the thick and thin disks occur in two main accretion episodes with both infall rates to be Gaussian. Both the pre-thin and post-thin scenarios for the formation of the Galactic disk are considered. The best-fitting is obtained through χ2\chi^2-test between the models and the new observed metallicity distribution function of G dwarfs in the solar neighbourhood (Hou et al 1998). Our results show that post-thin disk scenario for the formation of the Galactic disk should be preferred. Still, other comparison between model predictions and observations are given.Comment: 23 pages, 7 figure

    Momentum Distribution of Near-Zero-Energy Photoelectrons in the Strong-Field Tunneling Ionization in the Long Wavelength Limit

    Full text link
    We investigate the ionization dynamics of Argon atoms irradiated by an ultrashort intense laser of a wavelength up to 3100 nm, addressing the momentum distribution of the photoelectrons with near-zero-energy. We find a surprising accumulation in the momentum distribution corresponding to meV energy and a \textquotedblleft V"-like structure at the slightly larger transverse momenta. Semiclassical simulations indicate the crucial role of the Coulomb attraction between the escaping electron and the remaining ion at extremely large distance. Tracing back classical trajectories, we find the tunneling electrons born in a certain window of the field phase and transverse velocity are responsible for the striking accumulation. Our theoretical results are consistent with recent meV-resolved high-precision measurements.Comment: 5 pages, 4 figure

    Broadband optical chaos for stimulated Brillouin scattering suppression in power over fiber

    Get PDF
    Broadband chaos generated in an optically injected semiconductor laser is applied for power-over-fiber transmission. By varying the injection power, period-one oscillation, period-two oscillation, and chaotic oscillation are observed in the injected slave laser, indicating a period-doubling route to chaos. Compared to the free-running output of the laser, its chaotic output has a drastically increased signal bandwidth, which leads to a 19 dB increase of the stimulated Brillouin scattering threshold. Using a chaos of 5:2GHz bandwidth, a maximum optical power of 27dBm is obtained after 20km transmission over fiber, which is applicable to optically powering some advanced communication networks. The approach uses the inherent nonlinear laser dynamics, which requires no modulation electronics or microwave signal sources. © 2011 Optical Society of America.published_or_final_versio
    • …
    corecore