21,954 research outputs found

    Equilibrium magnetization in the vicinity of the first order phase transition in the mixed state of high-Tc superconductors

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    We present the results of a scaling analysis of isothermal magnetization M(H) curves measured in the mixed state of high-Tc superconductors in the vicinity of the established first order phase transition. The most surprising result of our analysis is that the difference between the magnetization above and below the transition may have either sign, depending on the particular chosen sample. We argue that this observation, based on M(H) data available in the literature, is inconsistent with the interpretation that the well known first order phase transition in the mixed state of high-Tc superconductors always represents the melting transition in the vortex system.Comment: 4 pages, 5 figure

    A General Treatment of the Distribution of Vacancies to Solute Atoms in a Ternary Solid Solution and its Application to Low Temperature Aging in Al-Cu-Sn Alloys(Metallurgy)

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    A general treatment to calculate the concentration of vacancy-solute atom pairs in a ternary dilute solid solution is presented. This treatment is applicable to a wide range of vacancy concentration relative to the concentration of one kind of solute atoms. The treatment is applied to explain the effect of tin addition on the rates of low temperature aging in Al-Cu alloys. The difference in the activation energy for aging between Al-Cu alloys and an Al-Cu-Sn alloy is analyzed to find the binding energy of a vacancy-tin atom pair to be about 0.3 eV larger than that of a vacancy-copper atom pair. The experimental result that the retardation of aging due to tin addition is appreciable only for tin concentrations larger than the vacancy concentration is also explained satisfactorily

    Formation of Deeply Bound Kaonic Atoms in (K^-,N) Reactions

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    We study theoretically the (K^-,N) reactions for the formation of the deeply bound kaonic atoms, which were predicted to be quasi--stable with narrow widths, using the Green function method. We consider various cases with different target nuclei and energies systematically and find the clear signals in the theoretical spectra for all cases considered in this article. The signals show very interesting structures, such as the RESONANCEDIPRESONANCE DIP instead of the resonance peak. We discuss the origins of the interesting structures and possibilities to get new information on the existence of the kaonic nuclei from the spectra of the atomic state formations.Comment: 11 pages, 9 figure

    Quasiparticle Interactions for f2^2-Impurity Anderson Model with Crystalline-Electric-Field: Numerical Renormalization Group Study

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    The aspect of the quasiparticle interaction of a local Fermi liquid, the impurity version of f2^2-based heavy fermions, is studied by the Wilson numerical renormalization group method. In particular, the case of the f2^2-singlet crystalline-electric-field ground state is investigated assuming the case of UPt3_3 with the hexagonal symmetry. It is found that the interorbital interaction becomes larger than the intraorbital one in contrast to the case of the bare Coulomb interaction for the parameters relevant to UPt3_3. This result offers us a basis to construct a microscopic theory of the superconductivity of UPt3_3 where the interorbital interactions are expected to play important roles.Comment: 9 pages, 5 figure

    Change of Electronic Structure Induced by Magnetic Transitions in CeBi

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    The temperature dependence of the electronic structure of CeBi arising from two types of antiferromagnetic transitions based on optical conductivity (σ(ω)\sigma(\omega)) was observed. The σ(ω)\sigma(\omega) spectrum continuously and discontinuously changes at 25 and 11 K, respectively. Between these temperatures, two peaks in the spectrum rapidly shift to the opposite energy sides as the temperature changes. Through a comparison with the band calculation as well as with the theoretical σ(ω)\sigma(\omega) spectrum, this peak shift was explained by the energy shift of the Bi 6p6p band due to the mixing effect between the Ce 4fΓ84f \Gamma_8 and Bi 6p6p states. The single-layer antiferromagnetic (++-) transition from the paramagnetic state was concluded to be of the second order. The marked changes in the σ(ω)\sigma(\omega) spectrum at 11 K, however, indicated the change in the electronic structure was due to a first-order-like magnetic transition from a single-layer to a double-layer (++++--) antiferromagnetic phase.Comment: 4 pages, to be published in J. Phys. Soc. Jpn. 73 Aug. (2004

    Hydrogen in Cyclotron-Irradiated Niobium

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    開始ページ、終了ページ: 冊子体のページ付

    Higher Security Thresholds for Quantum Key Distribution by Improved Analysis of Dark Counts

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    We discuss the potential of quantum key distribution (QKD) for long distance communication by proposing a new analysis of the errors caused by dark counts. We give sufficient conditions for a considerable improvement of the key generation rates and the security thresholds of well-known QKD protocols such as Bennett-Brassard 1984, Phoenix-Barnett-Chefles 2000, and the six-state protocol. This analysis is applicable to other QKD protocols like Bennett 1992. We examine two scenarios: a sender using a perfect single-photon source and a sender using a Poissonian source.Comment: 6 pages, 2 figures, v2: We obtained better results by using reverse reconciliation as suggested by Nicolas Gisi

    Neutron scattering study of soft phonons and diffuse scattering in insulating La1.95_{1.95}Sr0.05_{0.05}CuO4_{4}

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    Soft phonons and diffuse scattering in insulating La2x_{2-x}Srx_{x}CuO4_4 (x=0.05x=0.05) have been studied by the neutron scattering technique. The X-point phonon softens from high temperature towards the structural transition temperature Ts=410T_{s}=410 K, and the Z-point phonon softens again below 200 K. The Z-point phonon softening persists to low temperature, in contrast to the behavior observed in the superconducting x=0.15x=0.15 compound, in which the Z-point phonon hardens below TcT_c. The diffuse scattering associated with the structural phase transition at 410 K appears at commensurate positions. These results highlight interesting differences between superconducting and insulating samples.Comment: 5 pages, 5 figure

    Competition between charge/spin-density-wave orders and superconductivity in La1.875_{1.875}Ba0.125x_{0.125-x}Srx_{x}CuO4_{4}

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    We have performed a series of elastic neutron scattering measurements on 1/8-hole doped La1.875_{1.875}Ba0.125x_{0.125-x}Srx_{x}CuO4_{4} single crystals with {\it x} = 0.05, 0.06, 0.075 and 0.085. % Both charge-density-wave (CDW) and spin-density-wave (SDW) orders are found to develop simultaneously below the structural transition temperature between the low-temperature orthorhombic (LTO) and low-temperature tetragonal (LTT) or low-temperature less-orthorhombic (LTLO) phases. % In the ground state the CDW order is observed only in the LTT/LTLO phase and drastically degrades towards the LTO boundary. The {\it x}-dependence of {\it T}c_{c} strongly suggests a direct effect of the CDW order on the suppression of superconductivity. % Results are discussed in comparison with those from the La1.6x_{1.6-x}Nd0.4_{0.4}Srx_{x}CuO4_{4} system within the framework of the stripe model.Comment: 4 pages, 5figure
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