Abrupt transition in quasiparticle dynamics at optimal doping in a cuprate superconductor system

We report time-resolved measurements of the photoinduced change in reflectivity, Delta R, in the Bi2Sr2Ca(1-y)Dy(y)Cu2O(8+delta) (BSCCO) system of cuprate superconductors as a function of hole concentration. We find that the kinetics of quasiparticle decay and the sign of Delta R both change abruptly where the superconducting transition temperature Tc is maximal. These coincident changes suggest that a sharp transition in quasiparticle dynamics takes place precisely at optimal doping in the BSCCO system.Comment: 10 pages, 4 figure

The heliospheric modulation of cosmic ray protons during increased solar activity: effects of the position of the solar wind termination shock and of the heliopause

International audienceThe effects on the modulation of cosmic ray protons of different positions for the solar wind termination shock and for the heliopause are illustrated for moderate solar maximum conditions. This is done with a numerical model which includes diffusive termination shock acceleration, a heliosheath and drifts. The modulation is computed for the heliospheric equatorial plane and at 35° heliolatitude and for both magnetic polarity cycles of the Sun. It was found that the differences between the modulation for the two solar polarity cycles are less significant at a heliolatitude of 35° than in the equatorial plane. The modulation for the different heliopause positions are qualitatively similar, although there are clear quantitative differences which should be observable with the two Voyager spacecraft in the outer heliosphere. It is illustrated that the motion of the termination shock from 90 AU to 100 AU, with the heliopause fixed at 120 AU, is not crucially important to global modulation. What is of primary importance is the location of the heliopause. It can also be concluded from the results that significant asymmetric modulation is to be expected between the up-wind and down-wind directions of the heliosphere but this may become measureable only when spacecraft move beyond the termination shock into the heliosheath. Keywords. Interplanetary physics (Cosmic rays; Heliopause and solar wind termination) ? Space plasma physics (Transport processes

Observation of ferromagnetic resonance in strontium ruthenate (SrRuO3)

We report the observation of ferromagnetic resonance (FMR) in SrRuO3 using the time-resolved magneto-optical Kerr effect. The FMR oscillations in the time-domain appear in response to a sudden, optically induced change in the direction of easy-axis anistropy. The high FMR frequency, 250 GHz, and large Gilbert damping parameter, alpha ~ 1, are consistent with strong spin-orbit coupling. We find that the parameters associated with the magnetization dynamics, including alpha, have a non-monotonic temperature dependence, suggestive of a link to the anomalous Hall effect.Comment: submitted to Phys. Rev. Let

Dielectric sensitization of zeolitic imidazolate framework-8 (ZIF-8) nanopowder.

Metallo-organic complexes are a class of materials that are increasingly used in sensory applications. Zeolitic imidazolate frameworks (ZIFs) are their subclass that are topologically isomorphic with zeolites. The porosity of the crystals and their chemical structure, as well as their thermal and chemical stability, make some of these materials (ZIFs) very suitable for making sensors. The large specific area of micro and nano particles is an important parameter for sensor applications. Despite the fact that the dielectric characterization of powders in the RF domain was neglected in scientific works, this method can have great practical importance. This paper presents the results of the dielectric characterization of the ZIF-8 nanopowder in the frequency range of 24 Hz to 24 KHz. The results indicate that the presence of evaporation of water, ethanol and methanol leads to major changes in the dielectric permittivity of ZIF-8 nanopowder

The prevalence of femoroacetabular impingement anatomy in Division 1 aquatic athletes who tread water

Abstract Femoroacetabular impingement (FAI) is a disorder that causes hip pain and disability in young patients, particularly athletes. Increased stress on the hip during development has been associated with increased risk of cam morphology. The specific forces involved are unclear, but may be due to continued rotational motion, like the eggbeater kick. The goal of this prospective cohort study was to use magnetic resonance imaging (MRI) to identify the prevalence of FAI anatomy in athletes who tread water and compare it to the literature on other sports. With university IRB approval, 20 Division 1 water polo players and synchronized swimmers (15 female, 5 male), ages 18–23 years (mean age 20.7 ± 1.4), completed the 33-item International Hip Outcome Tool and underwent non-contrast MRI scans of both hips using a 3 Tesla scanner. Recruitment was based on sport, with both symptomatic and asymptomatic individuals included. Cam and pincer morphology were identified. The Wilcoxon Signed-Rank/Rank Sum tests were used to assess outcomes. Seventy per cent (14/20) of subjects reported pain in their hips yet only 15% (3/20) sought clinical evaluation. Cam morphology was present in 67.5% (27/40) of hips, while 22.5% (9/40) demonstrated pincer morphology. The prevalence of cam morphology in water polo players and synchronized swimmers is greater than that reported for the general population and at a similar level as some other sports. From a clinical perspective, acknowledgment of the high prevalence of cam morphology in water polo players and synchronized swimmers should be considered when these athletes present with hip pain

Determination of the spin-flip time in ferromagnetic SrRuO3 from time-resolved Kerr measurements

We report time-resolved Kerr effect measurements of magnetization dynamics in ferromagnetic SrRuO3. We observe that the demagnetization time slows substantially at temperatures within 15K of the Curie temperature, which is ~ 150K. We analyze the data with a phenomenological model that relates the demagnetization time to the spin flip time. In agreement with our observations the model yields a demagnetization time that is inversely proportional to T-Tc. We also make a direct comparison of the spin flip rate and the Gilbert damping coefficient showing that their ratio very close to kBTc, indicating a common origin for these phenomena

High quality superconducting niobium films produced by Ultra High Vacuum Cathodic Arc

The vacuum arc is a well-known technique to produce coating with enhanced adhesion and film density. Many cathodic arc deposition systems are actually in use in industry and research. They all work under (high) vacuum conditions in which water vapor pressure is an important source of film contamination, especially in the pulsed arc mode of operation. Here we present a Cathodic Arc system working under Ultra High Vacuum conditions (UHVCA). UHVCA has been used to produce ultra-pure niobium films with excellent structural and electrical properties at a deposition temperature lower than 100oC. The UHVCA technique therefore opens new perspectives for all applications requiring ultra-pure films or, as in the case of Plasma Immersion Ion Implantation, ultra-pure plasmas.Comment: submitted to AP