Anomalous magnetic behaviours of the cuprate superconductors-Meissner effect Hc1and Hc2

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Abstract
In order to elucidate whether the superconductivity of the cuprate HTSC is 'normal' or 'abnormal', systematic studies have been performed on the Meissner effect, lower and higher critical fields. The Meissner fraction is strongly dependent on the size of sample and on the field, which is explained by a novel model considering the sharp increase in the vortex pinning force while the flux expulsion process proceeds as T is lowered. Another new method has been proposed to determine Hc1 from the magnetization curve above Hc1, based on which the abrupt upturn of the Hc1-T curve frequently reported in the low T region has been attributed to the error induced by the strong pinning. The ambiguity associated with the Hc2-T curve is discussed in terms of the 'giant fluctuation' of superconductivity.