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(1995)Journal ArticleThe scaling behaviour of vortex-glass superconductivity is studied, by measuring the resistive transition as well as the I-V curve under a variety of magnetic fields, in a series of V doped YBa2Cu307_y samples with different grain sizes. The equilibrium phase boundary line between the normal and superconducting phases in the H-T plane obtained by fitting the resistive transition is consistent with that obtained by the I-V curve measurements. As the magnetic field is lower than a certain value, Hs, the scaling exponents are magnetic-field independent, but at H = H s, they begin to increase with the magnetic field and gradually get saturation. The switch field, Hs, decreases with decreasing the grain size in the samples. The results show that the magnetic-field-dependent scaling behaviour of the I-V curve observed in weak-link containing systems originates from the transition of a "weak" vortex-glass state to a "strong" vortex-glass state.
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(1997)Journal ArticleA resistivity anomaly near the superconducting transition temperature is observed in the ab-plane of as-grown Bi2Sr2CaCu2O8 (Bi-2 2 1 2) single crystals. The resistivity at the peak is much larger than the normal state resistivity around 100 K. The peak vanished gradually with increasing the applied magnetic field. I---V curves of the Bi-2 2 1 2 samples also exhibit a peak close to the transition steps, vanishing gradually with increasing intrinsic granularity of high-Tc superconductors.
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(1997)Journal ArticleSamples of Bi1.7Pb0.3Sr2Ca2Cu3O10+y (2223) annealed in different atmospheres and having different value of Tc and oxygen contents were obtained and examined by a wide range of measurements as well as theoretical calculation. A roughly quantitative relationship among Tc, oxygen content, c direction thermal expansion coefficient, and mismatch factors are established. It is revealed that the mismatch is important for superconductivity.
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(1997)Journal ArticleSuperconducting transition temperature (Tc), hole concentration (nc), and crystal structure for Bi1.7Pb0.3Sr2Ca2Cu3Oy (2223) polycrystals and Bi2Sr2CaCu2Oy (2212) single crystals annealed in different atmospheres have been measured. It is found that the consequence of annealing in O2 is mainly the modification of the oxygen in Cu---O planes, which is different from that in N2 where the change is in the Bi-O planes. The result provides a good explanation for the complicated changes of the Tc with the annealing conditions.
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(1997)Journal ArticleVoltage noise of the Bi2Sr2CaCu2O3+x single crystal below Tc is by an asymptotic power spectrum method. The low-frequency noise, power, Sa(T), shows a peak at Y = Tp. This peak is found to be closely related to the vortex lattice melting temperature. Near the peak T = Tp the power spectrum, Sa(f), exhibits a power-law fall-off, while at much lower temperatures Sa(f) dramaticaily deviates from the power-law behaviour, showing some broad peaks which are superposed upon a background with an exponential-law characteristic. The estimated correlation dimension of the noise data reveals that the vortex motion is highly correlatas at the early stage of melting, then develops into an extended dissipative dynamic system with self-organized criticality, showing a 1/fa behaviour. The correlated motion disappears when the lattice completely melts.
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(1995)Journal Article
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