149 research outputs found

    Mixed-state microwave response in superconducting cuprates

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    We report measurements of the magnetic-field induced microwave complex resistivity in REBa2_{2}Cu3_{3}O7δ_{7-\delta} thin films, with RE = Y, Sm. Measurements are performed at 48 GHz by means of a resonant cavity in the end-wall-replacement configuration. The magnetic field dependence is investigated by applying a moderate (0.8 T) magnetic field along the c-axis. The measured vortex state complex resistivity in YBa2_{2}Cu3_{3}O7δ_{7-\delta} and SmBa2_{2}Cu3_{3}O7δ_{7-\delta} is analyzed within the well-known models for vortex dynamics. It is shown that attributing the observed response to vortex motion alone leads to inconsistencies in the as-determined vortex parameters (such as the vortex viscosity and the pinning constant). By contrast, attributing the entire response to field-induced pair breaking leads to a nearly quantitative description of the data.Comment: 6 pages, 4 figures, to be published in J. Supercond. as proceedings of 8th HTSHFF (May 26th-29th, 2004, Begur, Spain

    Anisotropic renormalized fluctuations in the microwave resistivity in YBCO

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    We discuss the excess conductivity above Tc due to renormalized order-parameter fluctuations in YBCO at microwave frequencies. We calculate the effects of the uniaxial anisotropy on the renormalized fluctuations in the Hartree approximation, extending the isotropic theory developed by Dorsey [Phys. Rev. B 43, 7575 (1991)]. Measurements of the real part of the microwave resistivity at 24 and 48 GHz and of the dc resistivity are performed on different YBCO films. The onset of the superconducting transition and the deviation from the linear temperature behavior above Tc can be fully accounted for by the extended theory. According to the theoretical calculation here presented, a departure from gaussian toward renormalized fluctuations is observed. Very consistent values of the fundamental parameters (critical temperature, coherence lenghts, penetration depth) of the superconducting state are obtained.Comment: RevTex, 8 pages with 5 figures included, to be published in Physical Review

    c-axis transport and phenomenology of the pseudo-gap state in Bi2Sr2CaCu2O8+δBi_2Sr_2CaCu_2O_{8+\delta}

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    We measure and analyze the resistivity of Bi2Sr2CaCu2O8+δBi_2Sr_2CaCu_2O_{8+\delta} crystals for different doping δ\delta. We obtain the fraction of carrier η(T,δ)=ng/nTOT\eta(T,\delta) = n_g/n_{TOT} that do not participate to the c-axis conductivity. All the curves η(T,δ)\eta(T,\delta) collapse onto a universal curve when plotted against a reduced temperature x=[TΘ(δ)]/Δ(δ)x=[T-\Theta(\delta)]/\Delta^{*}(\delta). We find that at the superconducting transition ngn_g is doping independent. We also show that a magnetic field up to 14 T does not affect the degree of localization in the (a,b) planes but widens the temperature range of the x-scaling by suppressing the superconducting phase coherence.Comment: 11 pages, 5 figures, submitted to Phys.Rev.

    Tunnel and thermal c-axis transport in BSCCO in the normal and pseudogap state

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    We consider the problem of c-axis transport in double-layered cuprates, in particular with reference to Bi2_{2}Sr2_{2}CaCu2_{2}O8+δ_{8+\delta} compounds. We exploit the effect of the two barriers on the thermal and tunnel transport. The resulting model is able to describe accurately the normal state c-axis resistivity in Bi2_{2}Sr2_{2}CaCu2_{2}O8+δ_{8+\delta}, from the underdoped side up to the strongly overdoped. We extend the model, without introducing additional parameters, in order to allow for the decrease of the barrier when an external voltage bias is applied. The extended model is found to describe properly the c-axis resistivity for small voltage bias above the pseudogap temperature TT^{*}, the c-axis resistivity for large voltage bias even below TcT_c, and the differential dI/dVdI/dV curves taken in mesa structures.Comment: 12 pages, 6 figures. Submitted to Superconductor Science and Technolog

    VORTEX-MOTION DISSIPATION IN HIGH-TC SUPERCONDUCTORS AT MICROWAVE-FREQUENCIES

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    Measurements of the microwave surface resistance on samples of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O at different frequencies (23 and 48 GHz) indicate a universal behavior of the dissipation due to the vortex motion as a function of temperature, at low magnetic field. A temperature T0 = (0.97 +/- 0.01)T(c) separates two regimes such that for T < T0 the dissipation increases with T while, for T0 < T < T(c) the dissipation decreases with increasing T. The role of fluctuations is expedient for explaining the experimental data near T(c)
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