Superconducting transition and phase diagram of single-crystal MgB2
Résumé
The superconducting phase diagram of MgB2 was determined from magnetization, magnetotransport, and single-crystal specific-heat measurements. A zero-temperature in-plane coherence length of 9.4 nm is determined. The superconducting anisotropy g increases from a value around 2 near Tc to above 4.5 at 22 K. For Hic a pronounced peak effect in the critical current occurs at the upper critical field. Evidence for a surface superconducting state is presented for Hic that might account for the widespread in reported values of g.
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