LaFeAsO$_{1-x}$F$_{x}$ thin films: high upper critical fields and evidence of weak link behavior

Abstract

High-quality superconducting LaFeAsO$_{1-x}$F$_{x}$ thin films were grown on single crystalline LaAlO$_{3}$ 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, $\mu_{0}H_{c2}$(0) around 77 T and a remarkable steep slope of -7.5 T/K near $T_{c}$. From transport measurements we observed a weak link behavior in low magnetic fields and the evidence for a broad reversible regime.