329 research outputs found

    Superconductivity at T_c ~ 14 K in Single Crystalline FeTe0.61_{0.61}Se0.39_{0.39}

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    Single crystalline FeTe0.61_{0.61}Se0.39_{0.39} with a sharp superconducting transition at TcT_{\textrm{c}} \sim 14 K is synthesized via slow furnace cooling followed by low-temperature annealing. The effect of annealing on the chemical and superconducting inhomogeneities is carefully characterized. We also report resistivity, magnetization, and magneto-optical images of this crystal. Based on the Bean model, critical current density is estimated to exceed 1×1051 \times 10^5 A/cm2^2 below 5 K under zero field. Weak fish-tail effect is identified at lower temperatures.Comment: 4 pages, 4 figure

    Two-gap superconductivity in single crystal Lu2_2Fe3_3Si5_5 from penetration depth measurements

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    Single crystal of Lu2_2Fe3_3Si5_5 was studied with the tunnel-diode resonator technique in Meissner and mixed states. Temperature dependence of the superfluid density provides strong evidence for the two-gap superconductivity with almost equal contributions from each gap of magnitudes Δ1/kBTc=1.86\Delta_1/k_BT_c=1.86 and Δ1/kBTc=0.54\Delta_1/k_BT_c=0.54. In the vortex state, pinning strength shows unusually strong temperature dependence and is non-monotonic with the magnetic field (peak effect). The irreversibility line is sharply defined and is quite distant from the Hc2(T)H_{c2}(T), which hints on to enhanced vortex fluctuations in this two-gap system. Altogether our findings provide strong electromagnetic - measurements support to the two-gap superconductivity in Lu2_2Fe3_3Si5_5 previously suggested from specific heat measurements

    Microwave Induced Instability Observed in BSCCO 2212 in a Static Magnetic Field

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    We have measured the microwave dissipation at 10 GHz through the imaginary part of the susceptibility, χ"\chi^", in a BSCCO 2212 single crystal in an external static magnetic field HH parallel to the c-axis at various fixed temperatures. The characteristics of χ"(H)\chi^"(H) exhibit a sharp step at a field HstepH_{step} which strongly depends on the amplitude of the microwave excitation hach_{ac}. The characteristics of hach_{ac} vs. HstepH_{step}, qualitatively reveal the behavior expected for the magnetic field dependence of Josephson coupling.Comment: 4 pages, 3 Postscript figure

    Two-band superconductivity featuring different anisotropies in the ternary iron silicide Lu2_{2}Fe3_{3}Si5_{5}

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    We report detailed studies of the upper critical field and low-temperature specific heat in the two-gap superconductor Lu2_{2}Fe3_{3}Si5_{5}. The anisotropy of the upper critical field suggests that the active band is quasi-one-dimensional. Low-temperature specific heat in magnetic fields reveals that the virtual Hc2H_{c2} in the passive band is almost isotropic. These results strongly indicate that the two bands have two different anisotropies, similar to the typical two-gap superconductor MgB2_{2}, and their interplay may be essential to the two-gap superconductivity in Lu2_{2}Fe3_{3}Si5_{5}.Comment: 5 pages, 5 figure
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