ﻻ يوجد ملخص باللغة العربية
We present measurements of the magnetic field dependent microwave surface resistance in laser-ablated YBa$_2$Cu$_3$O$_{7-delta}$ films on SrTiO$_3$ substrates. BaZrO$_3$ crystallites were included in the films using composite targets containing BaZrO$_3$ inclusions with mean grain size smaller than 1 $mu$m. X-ray diffraction showed single epitaxial relationship between BaZrO$_3$ and YBa$_2$Cu$_3$O$_{7-delta}$. The effective surface resistance was measured at 47.7 GHz for 60$< T <$90 K and 0$< mu_0H <$0.8 T. The magnetic field had a very different effect on pristine YBa$_2$Cu$_3$O$_{7-delta}$ and YBa$_2$Cu$_3$O$_{7-delta}$/BaZrO$_3$, while for $mu_0H=$0 only a reduction of $T_c$ in the YBa$_2$Cu$_3$O$_{7-delta}$/BaZrO$_3$ film was observed, consistent with dc measurements. At low enough $T$, in moderate fields YBa$_2$Cu$_3$O$_{7-delta}$/BaZrO$_3$ exhibited an intrinsic thin film resistance lower than the pure film. The results clearly indicate that BaZrO$_3$ inclusions determine a strong reduction of the field-dependent surface resistance. From the analysis of the data in the framework of simple models for the microwave surface impedance in the mixed state we argue that BaZrO$_3$ inclusions determine very steep pinning potentials.
In order to study the vortex pinning determined by artificially introduced pinning centers in the small-vortex displacement regime, we measured the microwave surface impedance at 47.7 GHz in the mixed state of YBa$_{2}$Cu$_{3}$O$_{7-delta}$ thin film
We observe a strong reduction of the field induced thin film surface resistance measured at high microwave frequency ($ u=$47.7 GHz) in YBa$_{2}$Cu$_{3}$O$_{7-delta}$ thin films grown on SrTiO$_3$ substrates, as a consequence of the introduction of s
We probe the short-range pinning properties with the application of microwave currents at very high driving frequencies (47.7 GHz) on YBa$_2$Cu$_3$O$_{7-delta}$ films with and without sub-micrometer BaZrO$_3$ inclusions. We explore the temperature an
Microwave-field distribution, dissipation, and surface impedance are theoretically investigated for superconductors with laminar grain boundaries (GBs). In the present theory we adopt the two-fluid model for intragrain transport current in the grains
We report on the microwave surface resistance of two polycrystalline Mg11B2 samples; one consists of pristine material, the other has been irradiated at very high neutron fluence. It has already been reported that in the strongly irradiated sample th