2,344 research outputs found

    Experimentally observed evolution between dynamic patterns and intrinsic localized modes in a driven nonlinear electrical cyclic lattice

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    Locked intrinsic localized modes (ILMs) and large amplitude lattice spatial modes (LSMs) have been experimentally measured for a driven 1-D nonlinear cyclic electric transmission line, where the nonlinear element is a saturable capacitor. Depending on the number of cells and electrical lattice damping a LSM of fixed shape can be tuned across the modal spectrum. Interestingly, by tuning the driver frequency away from this spectrum an LSM can be continuously converted into ILMs and visa versa. The differences in pattern formation between simulations and experimental findings are due to a low concentration of impurities. Through this novel nonlinear excitation and switching channel in cyclic lattices either energy balanced or unbalanced LSMs and ILMs may occur. Because of the general nature of these dynamical results for nonintegrable lattices applications are to be expected. The ultimate stability of driven aero machinery containing nonlinear periodic structures may be one example.Comment: 7 pages 7 figure

    Comparative study of the effects of electron irradiation and natural disorder in single crystals of SrFe2_{2}(As1−x_{1-x}Px_x)2_2 (x=x=0.35) superconductor

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    London penetration depth, λ(T)\lambda(T), was measured in single crystals of SrFe2_2(As1−x_{1-x}Px_x)2_2 (x=x=0.35) iron - based superconductor. The influence of disorder on the transition temperature, TcT_c, and on λ(T)\lambda(T) was investigated. The effects of scattering controlled by the annealing of as-grown crystals was compared with the effects of artificial disorder introduced by 2.5~MeV electron irradiation. The low temperature behavior of λ(T)\lambda(T) can be described by a power-law function, Δλ(T)=ATn\Delta \lambda (T)=AT^n, with the exponent nn close to one in pristine annealed samples, as expected for superconducting gap with line nodes. Upon 1.2×10191.2 \times 10^{19} \ecm irradiation, the exponent nn increases rapidly exceeding a dirty limit value of n=n= 2 implying that the nodes in the superconducting gap are accidental and can be lifted by the disorder. The variation of the exponent nn with TcT_c is much stronger in the irradiated crystals compared to the crystals in which disorder was controlled by the annealing of the growth defects. We discuss the results in terms of different influence of different types of disorder on intra- and inter- band scattering

    Glauber dynamics in a single-chain magnet: From theory to real systems

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    The Glauber dynamics is studied in a single-chain magnet. As predicted, a single relaxation mode of the magnetization is found. Above 2.7 K, the thermally activated relaxation time is mainly governed by the effect of magnetic correlations and the energy barrier experienced by each magnetic unit. This result is in perfect agreement with independent thermodynamical measurements. Below 2.7 K, a crossover towards a relaxation regime is observed that is interpreted as the manifestation of finite-size effects. The temperature dependences of the relaxation time and of the magnetic susceptibility reveal the importance of the boundary conditions.Comment: Submitted to PRL 10 May 2003. Submitted to PRB 12 December 2003; published 15 April 200

    Universal observation of multiple order parameters in cuprate superconductors

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    The temperature dependence of the London penetration depth \lambda was measured for an untwined single crystal of YBa_2Cu_3O_{7-\delta} along the three principal crystallographic directions (a, b, and c). Both in-plane components (\lambda_a and \lambda_b) show an inflection point in their temperature dependence which is absent in the component along the c-direction (\lambda_c). The data provide convincing evidence that the in-plane superconducting order parameter is a mixture of s+d-wave symmetry whereas it is exclusively s-wave along the c-direction. In conjunction with previous results it is concluded that coupled s+d-order parameters are universal and intrinsic to cuprate superconductors.Comment: 5 pages, 3 figure

    Observational Artifacts of NuSTAR: Ghost Rays and Stray Light

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    The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, flies two conical approximation Wolter-I mirrors at the end of a 10.15m mast. The optics are coated with multilayers of Pt/C and W/Si that operate from 3--80 keV. Since the optical path is not shrouded, aperture stops are used to limit the field of view from background and sources outside the field of view. However, there is still a sliver of sky (~1.0--4.0 degrees) where photons may bypass the optics altogether and fall directly on the detector array. We term these photons Stray-light. Additionally, there are also photons that do not undergo the focused double reflections in the optics and we term these Ghost Rays. We present detailed analysis and characterization of these two components and discuss how they impact observations. Finally, we discuss how they could have been prevented and should be in future observatories.Comment: Published in Journal of Astronomical Telescopes, Instruments, and Systems. Open Access. http://dx.doi.org/10.1117/1.JATIS.3.4.04400

    Effect of cation size variance on spin and orbital order in Eu1−x_{1-x}(La0.254_{0.254}Y0.746_{0.746})x_{x}VO3_3

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    We have investigated the RR-ion (RR = rare earth or Y) size variance effect on spin/orbital order in Eu1−x_{1-x}(La0.254_{0.254}Y0.746_{0.746})x_{x}VO3_3. The size variance disturbs one-dimensional orbital correlation in CC-type spin/GG-type orbital ordered states and suppresses this spin/orbital order. In contrast, it stabilizes the other spin/orbital order. The results of neutron and resonant X-ray scattering denote that in the other ordered phase, the spin/orbital patterns are GG-type/CC-type, respectively.Comment: 4 pages, 4 figures, accepted to Rapid Communication in Physical Review
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