Photo--assisted current and shot noise in the fractional quantum Hall effect

The effect of an AC perturbation on the shot noise of a fractional quantum Hall fluid is studied both in the weak and the strong backscattering regimes. It is known that the zero-frequency current is linear in the bias voltage, while the noise derivative exhibits steps as a function of bias. In contrast, at Laughlin fractions, the backscattering current and the backscattering noise both exhibit evenly spaced singularities, which are reminiscent of the tunneling density of states singularities for quasiparticles. The spacing is determined by the quasiparticle charge $\nu e$ and the ratio of the DC bias with respect to the drive frequency. Photo--assisted transport can thus be considered as a probe for effective charges at such filling factors, and could be used in the study of more complicated fractions of the Hall effect. A non-perturbative method for studying photo--assisted transport at $\nu=1/2$ is developed, using a refermionization procedure.Comment: 14 pages, 6 figure

Spin-Charge Separation in the t−Jt-J Model: Magnetic and Transport Anomalies

A real spin-charge separation scheme is found based on a saddle-point state of the $t-J$ model. In the one-dimensional (1D) case, such a saddle-point reproduces the correct asymptotic correlations at the strong-coupling fixed-point of the model. In the two-dimensional (2D) case, the transverse gauge field confining spinon and holon is shown to be gapped at {\em finite doping} so that a spin-charge deconfinement is obtained for its first time in 2D. The gap in the gauge fluctuation disappears at half-filling limit, where a long-range antiferromagnetic order is recovered at zero temperature and spinons become confined. The most interesting features of spin dynamics and transport are exhibited at finite doping where exotic {\em residual} couplings between spin and charge degrees of freedom lead to systematic anomalies with regard to a Fermi-liquid system. In spin dynamics, a commensurate antiferromagnetic fluctuation with a small, doping-dependent energy scale is found, which is characterized in momentum space by a Gaussian peak at ($\pi/a$, $\pi/a$) with a doping-dependent width ($\propto \sqrt{\delta}$, $\delta$ is the doping concentration). This commensurate magnetic fluctuation contributes a non-Korringa behavior for the NMR spin-lattice relaxation rate. There also exits a characteristic temperature scale below which a pseudogap behavior appears in the spin dynamics. Furthermore, an incommensurate magnetic fluctuation is also obtained at a {\em finite} energy regime. In transport, a strong short-range phase interference leads to an effective holon Lagrangian which can give rise to a series of interesting phenomena including linear-$T$ resistivity and $T^2$ Hall-angle. We discuss the striking similarities of these theoretical features with those found in the high-$T_c$ cuprates and give aComment: 70 pages, RevTex, hard copies of 7 figures available upon request; minor revisions in the text and references have been made; To be published in July 1 issue of Phys. Rev. B52, (1995

One-dimensional Photonic Crystal For The 1.3-1.5 μm Region

Multilayer of PbTe quantum dots embedded in SiO2 were fabricated by alternatively use of Plasma Enhanced Chemical Vapor Deposition and Laser Ablation techniques. The optimal growing parameters for both the SiO2 films and the PbTe quantum dots were obtained. The refractive index and optical absorption of the sample were studied. Multilayer X-ray diffraction patterns were used to estimate the nanoparticles diameter. Morphological properties of the nanostructured material were studied using Transmission Electron Microscopy. Both absorption spectra and X-ray diffraction patterns reveled the nanoparticles are 6-8 nm in diameter, consequently appropriate for developing optical devices in the infra red region. Finally the multilayer was grown inside a Fabry Perot cavity. The transmittance of the one-dimensional photonic crystal was measured.6129Tsunetomo, K., Shunsuke, S., Koyama, T., Tanaka, S., Sasaki, F., Kobayashi, S., Ultrafast nonlinear optical response of CdTe microcrystallite-doped glasses fabricated by laser evaporation (1995) Molecular Crystals and Liquid Crystals Science and Technology Section B, Nonlinear Optics, 13 (1-3), pp. 109-126Gleiter, H., (1989) Prog. Mater. Sci., 33, p. 223Tudury, G.E., Marquezini, M.V., Ferreira, L.G., Barbosa, L.C., Cesar, C.L., Effect of band anisotropy on electronic structure of PbS, PbSe, and PbTe quantum dots (2000) Phys. Rev. B, 62 (11), pp. 7357-7364Rodriguez, E., Jimenez, E., Padilha, L.A., Neves, A.A.R., Jacob, G.J., Cesar, C.L., Barbosa, L.C., SiO2/PbTe quantum dots multilayer production and characterization (2005) Appl. Phys. Lett., 86, pp. 113117-113120Rodriguez, E., Jimenez, E., Cesar, C.L., Barbosa, L.C., 1D photonic band gap silica doped PbTe quantum dot optical device (2005) Glass Technology, 46 (2), pp. 47-49Rodriguez, E., Jimenez, E., Neves, A.A.R., Jacob, G.J., Cesar, C.L., Barbosa, L.C., Fabrication and characterization of PbTe quantum dot multilayers for Photonic Fabry-Perot Devices (2005) Physica E, 26, pp. 361-36

Menus for Feeding Black Holes

Black holes are the ultimate prisons of the Universe, regions of spacetime where the enormous gravity prohibits matter or even light to escape to infinity. Yet, matter falling toward the black holes may shine spectacularly, generating the strongest source of radiation. These sources provide us with astrophysical laboratories of extreme physical conditions that cannot be realized on Earth. This chapter offers a review of the basic menus for feeding matter onto black holes and discusses their observational implications.Comment: 27 pages. Accepted for publication in Space Science Reviews. Also to appear in hard cover in the Space Sciences Series of ISSI "The Physics of Accretion onto Black Holes" (Springer Publisher

Field Measurements of Terrestrial and Martian Dust Devils

Surface-based measurements of terrestrial and martian dust devils/convective vortices provided from mobile and stationary platforms are discussed. Imaging of terrestrial dust devils has quantified their rotational and vertical wind speeds, translation speeds, dimensions, dust load, and frequency of occurrence. Imaging of martian dust devils has provided translation speeds and constraints on dimensions, but only limited constraints on vertical motion within a vortex. The longer mission durations on Mars afforded by long operating robotic landers and rovers have provided statistical quantification of vortex occurrence (time-of-sol, and recently seasonal) that has until recently not been a primary outcome of more temporally limited terrestrial dust devil measurement campaigns. Terrestrial measurement campaigns have included a more extensive range of measured vortex parameters (pressure, wind, morphology, etc.) than have martian opportunities, with electric field and direct measure of dust abundance not yet obtained on Mars. No martian robotic mission has yet provided contemporaneous high frequency wind and pressure measurements. Comparison of measured terrestrial and martian dust devil characteristics suggests that martian dust devils are larger and possess faster maximum rotational wind speeds, that the absolute magnitude of the pressure deficit within a terrestrial dust devil is an order of magnitude greater than a martian dust devil, and that the time-of-day variation in vortex frequency is similar. Recent terrestrial investigations have demonstrated the presence of diagnostic dust devil signals within seismic and infrasound measurements; an upcoming Mars robotic mission will obtain similar measurement types

Ultra Large Amplification Bandwidth Of Er3+ And Tm3+ At S And L Band From Teo2-wo3-na2o-nb 2o5 Glass Doped Optical Fibers

Tellurite glasses optical fibers became promising for optical amplifiers due to its high rare earth ions solubility and very large amplification bandwidth. Among several tellurite glasses the TeO2-WO 3-Na2O-Nb2O5 system show one of the largest bandwidth. Our previous characterization of lifetime using the Ω2, Ω4, Ω6, Judd-Ofelt parameters indicate a quantum efficiency maximum for 7500ppm Er3+ concentration. Therefore we decided to produce jointed Er3+ and Tm3+ single mode optical fibers with this glass system keeping the 7500ppm Er3+ concentration and varying the Tm3+ concentration from 2500ppm to 15000ppm. This single mode fiber was pumped by 120mW of the semiconductor laser at 790nm and we observed a flat ASE bandwidth from 1400 to 1570nm for the 5000ppm Tm3+ concentration.5723243247Jeong, H., Oh, K., Han, S.R., Morse, T.F., Broadband amplified spontaneous emission from an Er3+-Tm 3+ - Codoped silica fibar (2003) Opt. Lett., 28, pp. 161-163Reisfeld, R., Jorgensen, C.K., (1987) Handbook on the Physics and Chemistry of Rare Earths, 9, pp. 1-90. , K. A. Gschneidner, Jr. and L. Eyring (Eds.), Elsevier ScienceChen, C.Y., Petrin, R.R., Yeh, D.C., Sibley, W.A., Concentration-dependent energy-transfer processes in Er3+-and Tm3+ -doped heavy-metal fluoride (1989) Opt. Lett., 14, pp. 432-434Miniscalco, W.J., Quimby, R.S., General procedure for the analysis of Er3+ cross sections (1991) Opt. Lett, 16, pp. 258-26

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Measurement of D*+/- meson production in jets from pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

This paper reports a measurement of D*+/- meson production in jets from proton-proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV at the CERN Large Hadron Collider. The measurement is based on a data sample recorded with the ATLAS detector with an integrated luminosity of 0.30 pb^-1 for jets with transverse momentum between 25 and 70 GeV in the pseudorapidity range |eta| < 2.5. D*+/- mesons found in jets are fully reconstructed in the decay chain: D*+ -> D0pi+, D0 -> K-pi+, and its charge conjugate. The production rate is found to be N(D*+/-)/N(jet) = 0.025 +/- 0.001(stat.) +/- 0.004(syst.) for D*+/- mesons that carry a fraction z of the jet momentum in the range 0.3 < z < 1. Monte Carlo predictions fail to describe the data at small values of z, and this is most marked at low jet transverse momentum.Comment: 10 pages plus author list (22 pages total), 5 figures, 1 table, matches published version in Physical Review

Spectral modeling of scintillator for the NEMO-3 and SuperNEMO detectors

We have constructed a GEANT4-based detailed software model of photon transport in plastic scintillator blocks and have used it to study the NEMO-3 and SuperNEMO calorimeters employed in experiments designed to search for neutrinoless double beta decay. We compare our simulations to measurements using conversion electrons from a calibration source of $\rm ^{207}Bi$ and show that the agreement is improved if wavelength-dependent properties of the calorimeter are taken into account. In this article, we briefly describe our modeling approach and results of our studies.Comment: 16 pages, 10 figure

Pbte Quantum Dots - Sio2 Multilayers For Optical Devices Produced By Laser Ablation

Thin films of glass doped with PbTe quantum dots were successfully fabricated. The semiconducting quantum dots were grown by laser ablation of a PbTe target (99.99%) using the second harmonic of a Q-Switched Quantel Nd:YAG laser under high purity argon atmosphere. The glass matrix was fabricated by a plasma chemical vapor deposition method using vapor of tetramethoxysilane (TMOS) as precursor. The QD's and the glass matrix were alternately deposited onto a Si (100) wafer for 60 cycles. Cross-section TEM image clearly showed QD's layer well separated from each other with glass matrix layers. The influence of the ablation time on the size distribution of the quantum dots is studied. HRTEM revealed anisotropy in the size of the QD's: they were about 9nm in the high and 3-5 in diameter. Furthermore HRTEM studies revealed that the QD's basically growth in the (200) and (220) directions. The thickness of the glass matrix layer was about 20 nm. Absorption, photo luminescence and relaxation time of the multilayer were also measured.5734116123Alivisatos, A.P., (1996) Sci., 271, p. 933Warnock, J., Awschalom, D.D., (1985) Phys. Rev. B, 32, p. 5529Borrelli, N.F., May, D.W., Holland, H.J., Smith, D.W., (1987) J. Appl. Phys., 61, p. 399Potter, B.G., Simmons, J.H., (1988) Phys. Rev. B, 37, p. 10838Gleiter, H., (1989) Prog. Mater. Sci., 33, p. 223Tsunetomo, K., Shunsuke, S., Koyama, T., Tanaka, S., Sasaki, F., Kobayashi, S., (1995) Nonlinear Opt., 13, p. 109Reynoso, V.C.S., De Paula, A.M., Cuevas, R.F., Neto, J.A.M., Alves, O.L., Cesar, C.L., Barbosa, L.C., (1995) Electr. Lett., 31 (12), pp. 1013-1015Jacob, G.J., Cesar, C.L., Barbosa, L.C., (2002) Chem. Phys. Glass, 43 C, pp. 250-252Singh, R.K., Narayan, J., (1990) Phys. Rev. B, 41, p. 8843Barnes, J.P., (2002) Nanotechnology, 13, p. 465Tudury, G.E., Marquezini, M.V., Ferreira, L.G., Barbosa, L.C., Cesar, C.L., (2000) Phys. Rev. B, 62 (11), pp. 7357-7364Cesar, C.L., Jacob, G.J., Tudury, G.E., Marquezini, M.V., Barbosa, L.C., (2004) Atti della Fondazione G. Ronchi Journal, (4), pp. 519-528. , Anno LI