Clean-limit pair breaking and two-dimensional vortex dynamics in ferromagnet-superconductor heterostructures

Abstract

Superconductivity in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ films of thickness ${d}_{\mathrm{Y}}<500\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ sandwiched between ferromagnetic and nonmagnetic epitaxial layers has been probed. The irreversibility temperature ${T}_{\mathrm{irr}(\mathrm{H})}$ in the vortex state maps onto a clean-limit pair-breaking temperature ${T}_{\mathrm{c}(\mathrm{H})}$, and a universal relation exists between the pair-breaking field ${H}_{\mathrm{pb}}$ and an effective thickness ${d}_{\mathrm{eff}}(<{d}_{\mathrm{Y}})$ of the superconductor. The vortex response in these two-dimensional (2D) films indicates a crossover temperature $T*$, which separates two regimes of flux motion controlled by formation of dislocations $(T>T*)$, and migration of preexisting dislocations and dislocation pairs $(T<T*)$ in the 2D flux line lattice.