Phys. Rev. Lett. 81, 3231–3234 (1998)Lower Critical Field Hc1 and Barriers for Vortex Entry in Bi2Sr2CaCu2O8+δ CrystalsReceived 31 October 1997; published in the issue dated 12 October 1998 The penetration field Hp of Bi2Sr2CaCu2O8+δ 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. © 1998 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.81.3231
DOI:
10.1103/PhysRevLett.81.3231
PACS:
74.25.Bt, 74.60.Ec, 74.60.Ge, 74.72.Hs
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