143 research outputs found
Microwave surface resistance in BSCCO crystal: magnetic field and angular measurement.
No full textWe report on measurement of the microwave surface resistance R-s at 48 GHz on a BSCCO (2212 phase) crystal. We describe the procedure developed to perform measurements on crystals by the use of a resonant cavity with end-wall-replacement technique. The measurements are taken as a function of the temperature, magnetic field and angle theta between the field orientation and the (a,b) planes. The measured R-s is strongly anisotropic. The overall angular behavior reasonably follows the sin theta scaling rule, but deviation from this simple behavior appears approaching the parallel orientation. When the field is parallel to the (a,b) planes, a local maximum is observed in R-s, instead of a minimum. Finally, we show that the magnetic field dependence of R-s cannot be easily reconciled with existing theories for the motion of rigid flux lines
Scaling in the angular dependence of the critical current and temperature-dependent anisotropy ratio in Bi2Sr2CaCu2O8
No full textWe present measurements of the critical current in an epitaxial Bi2Sr2CaCu2O8 film as a function of the magnetic field, the temperature, and of the angle theta between the field and the a, b planes. The orientational study reveals an increasing anisotropy in J(c) with increasing temperature. The isothermal curves J(c)(H) taken at various angles 0-degrees less-than-or-equal-to theta less-than-or-equal-to 90-degrees are found to collapse to a single curve when the magnetic field is normalized to a scaling function f(theta): J(c)(H,theta)=J(c)[H/f(theta)]. The best fit for f(theta) is obtained using an expression originally derived for H(c2)(T,theta) by Tinkham. The increase in J(c)(0-degrees)/J(c)(90-degrees) with increasing temperature is reflected by the increase in the anisotropy ratio f(0-degrees)/f(90-degrees), consistent with the quasi-two-dimensional Tinkham expression. Consistently, the same model quantitatively describes the increasing anisotropy with increasing temperature
IV measurements in Bi:2212 film in magnetic fields: scaling behavior
No full textEds. L. Zhou, H.W.Weber, E.W.Colling
CONSISTENT EXPLANATION ON LORENTZ FORCE-FREE DISSIPATION IN H-PARALLEL-TO-L-PARALLEL-TO-C FOR VARIOUS HIGH-TC SUPERCONDUCTORS - COMMENT
No full textEffects of fluctuations and vortex glass-to-liquid transition on the magneto-dissipation in high-Tc superconductors
No full textRESISTIVE LOSSES AT MICROWAVE-FREQUENCIES IN GRANULAR HIGH-TC SUPERCONDUCTORS - FLUX-CREEP, FLUX-FLOW AND JOSEPHSON-JUNCTIONS
No full textThe resistive losses in a magnetic field H for granular superconductors can be attributed to three different processes: flux-flow, flux-creep and dephasing of Josephson junctions (JJ). The microwave absorption measurements are able to separate the three contributions to the losses, if the ranges of the magnetic field and the temperature are suitably selected. A calculation of the surface-resistance, based on the hypothesis of validity of the Bean model and which qualitatively explains the experimental results is given
MAGNETIC DISSIPATION IN HIGH-TC SUPERCONDUCTORS - EVIDENCE FOR A VORTEX-GLASS-TO-VORTEX-LIQUID TRANSITION
No full textThe experimental behaviors of the resistivity as a function of both magnetic field, rho(T)(H), and temperature, rho(H)(T), in Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O high-quality samples, are interpreted by means of a phenomenological theory based on two hypotheses: (i) the irreversibility line at zero frequency is the glass-to-liquid-vortex transition, (ii) the dissipation mechanism is that found by Ambegaokar and Halperin and applied by Tinkham to high-T(c) superconductors. The results of the fits performed on the whole range of resistivity variation (five decades) give strong support to the glass model
CRITICAL-FIELD FOR THE ONSET OF THE DISSIPATION AND 2-D BEHAVIOR IN BI-SR-CA-CU-O
No full textWe present measurements of the angular dependence of the critical field connected to the onset of the resistivity as a function of the magnetic field in Bi-Sr-Ca-Cu-O 2212. The measurements are performed by a four-probe dc resistance method. The sample is a highly c-axis oriented epitaxial film. When the measurements are carried out with the direction of the external magnetic field parallel to the Cu-O planes, the main result is the existence of a crossover temperature at which the superconductor goes from an anisotropic 3-D to a 2-D behavior with the lowering of the temperature
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