High Upper Critical Fields and Evidence of Weak-Link Behavior in Superconducting LaFeAsO1-xFx Thin Films

Superconducting LaFeAsO1-xFx thin films were grown on single crystalline LaAlO3 substrates with critical temperatures (onset) up to 28 K. Resistive measurements in high magnetic fields up to 40 T reveal a paramagnetically limited upper critical field mu H-0(c2)(0) around 77 T and a remarkable steep slope of -6.2 TK-1 near T-c. From transport measurements we observed weak-link behavior in low magnetic fields and evidence for a broad reversible regime.