297,457 research outputs found

    D-XY Critical Behavior in Cuprate Superconductors

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    We outline the universal and finite temperature critical properties of the 3D-XY model, extended to anisotropic extreme type-II superconductors, as well as the universal quantum critical properties in 2D. On this basis we review: (i) the mounting evidence for 3D-XY behavior in optimally doped cuprate superconductors and the 3D to 2D crossover in the underdoped regime; (ii) the finite size limitations imposed by inhomogeneities; (iii) the experimental evidence for a 2D-XY quantum critical point in the underdoped limit, where the superconductor to insulator transition occurs; (iv) the emerging implications and constraints for microscopic models.Comment: 5 pages, 6 figure

    Cosmological parameters from combined second- and third-order aperture mass statistics of cosmic shear

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    We present predictions for cosmological parameter constraints from combined measurements of second- and third-order statistics of cosmic shear. We define the generalized third-order aperture mass statistics and show that it contains much more information about the bispectrum of the projected matter density than the skewness of the aperture mass. From theoretical models as well as from LCDM ray-tracing simulations, we calculate and and their dependence on cosmological parameters. The covariances including shot noise and cosmic variance of M_ap^2, M_ap^3 and their cross-correlation are calculated using ray-tracing simulations. We perform an extensive Fisher matrix analysis, and for various combinations of cosmological parameters, we predict 1-sigma-errors corresponding to measurements from a deep 29 square degree cosmic shear survey. Although the parameter degeneracies can not be lifted completely, the (linear) combination of second- and third-order aperture mass statistics reduces the errors significantly. The strong degeneracy between Omega_m and sigma_8, present for all second-order cosmic shear measures, is diminished substantially, whereas less improvement is found for the near-degenerate pair consisting of the shape parameter Gamma and the spectral index n_s. Uncertainties in the source galaxy redshift z_0 increase the errors of all other parameters.Comment: Revised version, 15 pages, 10 figures, in press at A&A. Some changes were made including an extension of the analysis. Matches the published versio

    Identifying Transiting Circumbinary Planets

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    Transiting planets manifest themselves by a periodic dimming of their host star by a fixed amount. On the other hand, light curves of transiting circumbinary (CB) planets are expected to be neither periodic nor to have a single depth while in transit, making BLS [Kovacs et al. 2002] almost ineffective. Therefore, a modified version for the identification of CB planets was developed - CB-BLS. We show that using CB-BLS it is possible to find CB planets in the residuals of light curves of eclipsing binaries (EBs) that have noise levels of 1% or more. Using CB-BLS will allow to easily harness the massive ground- and space- based photometric surveys to look for these objects. Detecting transiting CB planets is expected to have a wide range of implications, for e.g.: The frequency of CB planets depend on the planetary formation mechanism - and planets in close pairs of stars provides a most restrictive constraint on planet formation models. Furthermore, understanding very high precision light curves is limited by stellar parameters - and since for EBs the stellar parameters are much better determined, the resultant planetary structure models will have significantly smaller error bars, maybe even small enough to challenge theory.Comment: To appear on the IAU Symposium 253 proceedings. 4 pages, 4 figure

    An analogue of the BGG resolution for locally analytic principal series

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    Let G be a connected reductive quasisplit algebraic group over a field L which is a finite extension of the p-adic numbers. We construct an exact sequence modelled on (the dual of) the BGG resolution involving locally analytic principal series representations for G(L). This leads to an exact sequence involving spaces of overconvergent p-adic automorphic forms for certain groups compact modulo centre at infinity.Comment: 36 pages; corrected proof of Theorem 26; extended results to locally analytic principal series for G(L); cut unnecessary expository materia

    Magnetic field induced 3D to 1D crossover in Sr0:9La0:1CuO2

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    The effect of the magnetic field on the critical behavior of Sr0:9La0:1CuO2 is explored in terms of reversible magnetization data. As the correlation length transverse to the magnetic field Hi,applied along the i-axis, cannot grow beyond the limiting magnetic length LHi, related to the average distance between vortex lines, one expects a magnetic field induced finite size effect. Invoking the scaling theory of critical phenomena we provide clear evidence for this effect. It implies that in type II superconductors there is a 3D to 1D crossover line Hpi(T). Consequently, below Tc and above Hpi(T) uperconductivity is confined to cylinders with diameter LHi(1D). Accordingly, there is no continuous phase transition in the (H,T)-plane along the Hc2-lines as predicted by the mean-field treatment.Comment: 4 pages, 5 figure

    Magnetic Field induced Dimensional Crossover Phenomena in Cuprate Superconductors and their Implications

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    We discuss the occurrence of crossing points in the magnetization - temperature (m,T(m,T) plane within the framework of critical phenomena. It is shown that in a two-dimensional superconducting slab of thickness dsd_{s} mz(Ύ)m_{z}(\delta) versus temperature TT curves measured in different fields H=H(0,sin⁥(Ύ),cos⁥(Ύ))\mathbf{H} = H(0,\sin (\delta) ,\cos (\delta)) will cross at the critical temperature T_c of the slab. In contrast, in a 3D anisotropic bulk superconductor the crossing point occurs in the plot mz(Ύ)/Hz1/2m_{z}(\delta) /H_{z}^{1/2} versus TT. The experimental facts that 2D crossing point features have been observed in ceramics and in single crystals for H\mathbf{H} close to H=H(0,0,1)\mathbf{H} = H(0,0,1), but not for H=H(0,1,0)\mathbf{H} = H(0,1,0), is explained in terms of an angle-dependent crossover field separating the regions where 2D or 3D thermal fluctuations dominate. The measured 2D-crossing point data are used to estimate one of the fundamental parameters of cuprate superconductors, the minimum thickness of the slab (ds)(d_{s}), which remains superconducting. Our estimates, based on experimental 2D-crossing point data for single crystals, reveal that this length adopts material dependent values. Therefore, experimental data for T_c and λ∄2(T=0)\lambda_{\Vert}^{2}(T=0), plotted in terms of T_c versus 1/λ∄2(T=0)1/\lambda_{\Vert}^{2}(T=0) will not tend to a straight line with universal slope as the underdoped limit is approached. Implications for magnetic torque measurements are also worked out

    Pressure effects on the superconducting properties of YBa_2Cu_4O_8

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    Measurements of the magnetization under high hydrostatic pressure (up to 10.2 kbar) in YBa_2Cu_4O_8 were carried out. From the scaling analysis of the magnetization data the pressure induced shifts of the transition temperature T_c, the volume V and the anisotropy \gamma have been obtained. It was shown that the pressure induced relative shift of T_c mirrors essentially that of the anisotropy. This observation uncovers a novel generic property of anisotropic type II superconductors, that inexistent in the isotropic case.Comment: 4 pages, 3 figure

    Probing inhomogeneities in type II superconductors by means of thermal fluctuations, magnetic fields and isotope effects

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    Type II superconductors, consisting of superconducting domains embedded in a normal or insulating matrix, undergo a rounded phase transition. Indeed, the correlation length cannot grow beyond the spatial extent of the domains. Accordingly, the thermodynamic properties will exhibit a finite size effect. It is shown that the specific heat and penetration depth data of a variety of type II superconductors, including cuprates, exhibit the characteristic properties of a finite size effect, arising from domains with nanoscale extent. The finite size scaling analysis reveals essential features of the mechanism. Transition temperature and superfluidity increase with reduced domain size. The combined finite size and isotope effects uncover the relevance of local lattice distortionsComment: 9 pages, 5 figur

    Libraries in Switzerland

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    Ausgehend von einem historischen Überblick schildert der Beitrag die Entwicklung der Schweizer Bibliotheken in der Zeit von 1970 bis 2010: soziopolitischer Kontext, Struktur des Bibliothekswesen, technischer Wandel, wichtigste Akteure und aktuelle Herausforderungen. Starting with a brief history of libraries in Switzerland, this report focusses on the development of Swiss libraries from 1970 to 2010: socio-political context, structure of the Swiss library sector, change driven by technology, main actors, and challenges at the beginning of the new millennium. Suite Ă  un aperçu historique, l'article dĂ©crit le dĂ©veloppement des bibliothĂšques suisses dans la pĂ©riode de 1970 Ă  2010: le contexte socio-politique, la structure du secteur des bibliothĂšques, les changements technologiques, les principaux acteurs et les dĂ©fis actuels