Superconducting transition and phase diagram of single-crystal (formula presented)

The superconducting phase diagram of (formula presented) 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 γ increases from a value around 2 near (formula presented) to above 4.5 at 22 K. For (formula presented) a pronounced peak effect in the critical current occurs at the upper critical field. Evidence for a surface superconducting state is presented for (formula presented) that might account for the widespread in reported values of γ.