1,721,035 research outputs found
GLASSY BEHAVIOR IN RESISTIVE MEASUREMENTS IN BI2SR2CACU2OX
No full textWe present a large set of measurements of resistance as a function of magnetic field at fixed temperatures, and as a function of temperature at fixed magnetic field, in epitaxial highly-oriented Bi:2212 films. A new model of the glassy dynamics of the flux lines is developed, where the leading dissipative term is the phase slippage of the flux lines over a disordered network of highly-damped Josephson junctions, with an activation process given by a Vogel-Fulcher equation. The glass-to-liquid temperature obtained by the fits reproduces the irreversibility line reported in the literature. The proposed phenomenological model is able to fit all the data from low temperatures up to T(c), for the accessible magnetic field range
VORTEX-MOTION DISSIPATION IN HIGH-TC SUPERCONDUCTORS AT MICROWAVE-FREQUENCIES
No full textMeasurements 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)
2D TO 3D CROSSOVER IN BI-SR-CA-CU-O - COMPARISON WITH SYNTHETIC MULTILAYERED SUPERCONDUCTORS
No full textWe show that in a highly c-oriented 2:2:1:2 Bi-Sr-Ca-Cu-O film the angular-dependent magnetic field H* at the onset of the resistivity behaves experimentally in a way completely analogous to the critical field found in synthetic multilayered superconductors. In particular, on varying the temperature, the field H* exhibits a crossover from a 2D to an anisotropic 3D behavior as a function of the angle-curly theta between the external magnetic field and the a-b plane
Fluctuation-induced resistivity in YBCO across T-c from angular measurements in magnetic field.
No full textWe present various sets of resistive transitions in an YBCO thin film, as a function of the temperature, magnetic field and field orientation theta with respect to the (a,b) planes. We show that the resistivity undergoes an angular scaling only above a characteristic field-dependent temperature T-f(H), where T-f is below the mean-field transition temperature T-C(H). The scaling function found is that expected for a strongly coupled layered superconductor. It is shown that the interacting fluctuations theory describes with details the data for T>T-f(H), with a very reduced set of parameters. Comparison with data taken on untwinned samples reveals that the upper part of the transition is identical for films and single crystals, and that the same theory works well in both cases. In addition, Bardeen-Stephen flux flow is observed in the crystal only, and in a small region of H and T. We conclude that in a wide portion of the H-T plane the dissipation is due to intrinsic properties only (order parameter fluctuations), while only at lower temperatures the pinning becomes relevant, as supported by the breakdown of the angular scaling and by the fact that pure crystals and films appear to be different at low temperatures only
MAGNETIC-FIELD FOR THE ONSET OF RESISTIVITY - ANGULAR-DEPENDENCE AND TEMPERATURE-INDUCED DIMENSIONAL CROSSOVER IN BI-SR-CA-CU-O
No full textThe temperature-induced crossover from a two-dimensional (2D) to 3D behavior found in 2:2:1:2 Bi-Sr-Ca-Cu-O is studied by means of a large set of measurements of the magnetic field H * for the onset of dissipation. Some interesting features of the angular dependence near the crossover temperature are found; in particular, the H* values perpendicular to a-b planes lie on the irreversibility line. The angular behavior of H* is analogous to that of the upper critical field in conventional layered superconductors. A tentative explanation is given
ANGLE-DEPENDENT MICROWAVE MAGNETO-DISSIPATION IN BI2SR2CACU2O8 FILMS - QUASI-2D ANGULAR SCALING PROPERTIES
No full textWe have measured the orientational dependence of the magnetic-field induced microwave dissipation at 21 GHz in a Bi2Sr2CaCu2O8+x epitaxial film, by means of a cavity technique. The dissipation is measured as a function of the external magnetic field H and of the angle (curly theta) between H and the (a, b) planes, at fixed temperatures. Measurements were taken in the range 49-81 K. Apart from a narrow (Delta(curly theta)approximate to 0.5 degrees) angular range close to the parallel orientation, the strongly anisotropic dissipation can be successfully scaled over the orthogonal-field curve with a simple rescaling of the magnetic field: H --> H/f(curly theta). Best scaling is obtained with the quasi-two-dimensional (quasi-2D), thin-film expression for f(curly theta). One single parameter, the anisotropy ratio epsilon, is used in the scaling. It is found that epsilon increases with temperature, consistent with the quasi-2D result, which gives a quantitative fitting for the data. The anisotropy ratios so obtained are compared with those previously obtained by the angular scaling of the critical currents in a sample from the same batch. The quantitative agreement between the two sets is excellent, strongly indicating that the same scaling properties apply in Bi2Sr2CaCu2O8 for very different dissipative properties
EXPERIMENTAL-EVIDENCE OF A SHARP TRANSITION INTO A FROZEN STATE AT LOW-TEMPERATURE AND HIGH MAGNETIC-FIELDS IN GRANULAR HIGH-TC SUPERCONDUCTORS
No full textWe present a set of experimental results of the microwave magneto-absorption at various temperatures for granular samples of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O. The role of magnetic and thermal history is evident. In the frame in which the absorption, as a function of the magnetic field, is due to the decoupling of Josephson junctions (JJ), we show that the array of JJs is driven in a frozen state by the magnetic field at low temperature. The transition to the frozen state occurs in a narrow range of temperature (15-20 K for Y-Ba-Cu-O and 25-30 K for Bi-Sr-Ca-Cu-O). The superconducting glass model for an array of JJs is able to qualitatively explain the experimental data
EFFECTS OF THE MAGNETIC AND THERMAL HISTORY IN GRANULAR SAMPLES OF Y-BA-CU-O AND BI-SR-CA-CU-O - EXPERIMENTAL-EVIDENCE OF A SHARP TRANSITION INTO A FROZEN STATE AT LOW-TEMPERATURE
No full textNormal-state c-axis transport in Bi2Sr2CaCu2O8+delta: Interlayer tunneling and thermally activated dissipation
No full textWe systematically investigate the effect of doping on the temperature dependence of the c-axis resistivity in Bi2Sr2CaCu2O8+delta. We present simultaneous measurements of the resistivity tensor components rho(c) and rho(ab) at different doping from the underdoped to the overdoped regime. The c-axis resistivity behaviors as a function of temperature are interpreted, in the normal state (T>T*), through a single phenomenological model based on the existence of two energy barriers with different heights and widths. Two complementary processes are considered for each barrier: incoherent tunneling and thermal activation. The resistive measurements at different doping are well fitted with a small number of free parameters with well defined physical meanings. The analysis of the behaviors of the fitting parameters as a function of doping gives support and consistency to the two-barrier model
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