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Lower critical field Hc1 and barriers for vortex entry in Bi2Sr2CaCu2O8+delta crystals

M. Nideroest, R. Frassanito, M. Saalfrank, A. C. Mota, G. Blatter, V. N. Zavaritsky, T. W. Li, P. H. Kes

cond-mat.supr-conarXiv:cond-mat/9811187

Abstract

The penetration field Hp of Bi2Sr2CaCu2O8+delta crystals is determined from magnetization curves for different field sweep rates dH/dt and temperatures. The obtained results are consistent with theoretical reports in the literature about vortex creep over surface and geometrical barriers. The frequently observed low-temperature upturn of Hp is shown to be related to metastable configurations due to barriers for vortex entry. Data of the true lower critical field Hc1 are presented. The low-temperature dependence of Hc1 is consistent with a superconducting state with nodes in the gap function. [PACS numbers: 74.25.Bt, 74.60.Ec, 74.60.Ge, 74.72.Hs]

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