177,043 research outputs found
Change of strength of vortex pinning in YBCO due to BaZrO3 inclusions
No full textWe probe the short-range pinning properties with the application of microwave currents at very high driving frequencies (47.7 GHz) on YBa2Cu3O7-delta films with and without sub-micrometer BaZrO3 inclusions. We explore the temperature and field ranges 60 K, < T < T-c and 0 <mu H-0 < 0.8 T, with the field applied along the c-axis. The magnetic field induces a much smaller increase of the microwave resistivity, Delta rho(1)(H)+i Delta rho(2)(H), in YBa2Cu3O7-delta/BaZrO3 with respect to pure YBa2Cu3O7-delta.Delta rho(1)(H) is slightly superlinear in pure YBa2Cu3O7-delta (suggesting a possible contribution of thermal activation), but linear or sublinear in YBa2Cu3O7-delta/BaZrO3 (suggesting a possible suppression of thermal activation as a consequence of BaZrO3 inclusions). These features persist up to close to T-c. We discuss our data in terms of the ratio r = Delta rho(2)(H)/Delta rho(1)(H) in the framework of the models for the microwave surface impedance in the mixed state. Large r are found in YBa2Cu3O7-delta/BaZrO3, with little field dependence. By contrast, smaller values and stronger field dependences are found in pure YBa2Cu3O7-delta. We discuss the different field dependence of the pinning constant. (C) 2008 Elsevier B.V. All rights reserved
Effects of a magnetic field on the microwave surface impedance of Bi2Sr2CaCu2O8+x single crystals
No full textMicrowave properties of DyBCO monodomain in the mixed state and comparison with other RE-BCO systems
No full textpeer reviewedWe report on microwave measurements on DyBa 2Cu 3O 7-δ monodomains grown by the top-seeded melt-textured technique. We measured the field increase of the surface resistance R s(H) in the a-b plane at 48.3 GHz. Measurements were performed at fixed temperatures in the range 70 K-T c with a static magnetic field μ 0H < 0.8 T parallel to the c-axis. Low field steep increase of the dissipation, typical signature of the presence of weak links, is absent, thus indicating the single-domain behavior of the sample under study. The magnetic field dependence of R s(H) is ascribed to the dissipation caused by vortex motion. The analysis of X s(H) points to a free-flow regime, thus allowing to obtain the vortex viscosity as a function of temperature. We compare the results with those obtained on RE-BCO systems. In particular, we consider strongly pinned films of YBa 2Cu 3O 7-δ with nanometric BaZrO 3 inclusions. © 2011 Elsevier B.V. All rights reserved
Reduction in the field-dependent microwave surface resistance inYBa2Cu3O7-delta with submicrometric BaZrO3 inclusions as a function of BaZrO3 concentration
No full textIn order to study the vortex pinning determined by artificiallyintroduced pinning centers in the small-vortex displacement regime, wemeasured the microwave surface impedance at 47.7 GHz in the mixed stateof YBa2Cu3O7-delta thin films, where submicrometric BaZrO3 particleshave been incorporated. As a function of the BaZrO3 content, weobserved that the absolute losses slightly decrease up to a BaZrO3content of 5%, and then increase. We found that themagnetic-field-induced losses behave differently in that they are notmonotonic with increasing BaZrO3 concentration. At small concentration(2.5%) the field-induced losses increase, but large reduction in thelosses themselves, by factors up to 3, is observed upon furtherincreasing the BaZrO3 concentration in the target up to 7%. Usingmeasurements of both surface resistance and surface reactance, weestimate vortex pinning-related parameters. We found that BaZrO3inclusions introduce deep and steep pinning wells. In particular, theminimum height of the energy barrier for single vortices is raised. Atlarger BaZrO3 content (5% and 7%) the phenomenon is at its maximum, butit is unclear whether it shows a saturation or not, leaving room forfurther improvements. (C) 2009 American Institute of Physics. [DOI:10.1063/1.3056179
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Strong reduction of field-dependent microwave surface resistance in YBa2Cu3O7−δ with sub-micrometric BaZrO3 inclusions
No full textWe observe a strong reduction of the field induced thin film surface resistance measured at high
microwave frequency (nu = 47.7 GHz) in YBa2Cu3O7−d thin films grown on SrTiO3 substrates, as a
consequence of the introduction of submicrometric BaZrO 3 particles. The field increase of the
surface resistance is smaller by a factor of ϳ3 in the film with BaZrO3 inclusions, while the
zero-field properties are not much affected. Combining surface resistance and surface reactance
data, we conclude (a) that BaZrO3 inclusions determine very deep and steep pinning wells and (b)
that the pinning changes nature with respect to the pure film
Effects of a magnetic field on the microwave surface impedance of Bi2Sr2CaCu2O8+x single crystals.
No full textWe present measurements of the field-induced change of the microwave surface impedance in optimally doped Bi2Sr2CaCu2O8- crystals. Measurements are taken with microwave fields in the (a,b) planes. A moderate (<0.7 T) dc magnetic field is applied normal to the (a,b) planes. Measurements are taken for temperatures above 70 K. At fixed temperature, with increasing field the surface resistance presents a sharp onset at low fields, a steep rise then a plateau or a peak, followed by a second, slower rise with the field. The surface reactance presents similarly a steep raise at low fields above the onset, then a sudden decrease. We discuss the applicability of commonly established vortex motion models to the observed response, and we find that substantial inconsistencies emerge. Possible influences of the layered nature on the vortex response are investigated
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