Intrinsic Size Effects In Type-2 Superconducting Films

Null-deflection torque-magnetometer measurements performed on well-annealed low-$\ensuremath{\kappa}$ type-II superconducting films in nearly parallel magnetic fields suggest that flux entry may be delayed to a field ${H}_{s}$ which can be greater than ${H}_{c}$. It is found that ${H}_{s}$ depends on the film thickness, the coherence length, and $\ensuremath{\kappa}$. Furthermore, our results indicate that in films having a thickness less than 20 coherence lengths, two critical fields ${H}_{s}$ and ${H}_{c3}$ are observed, but not ${H}_{c2}$. The Arbikosov mixed state may be therefore suppressed in favor of a new state which resembles a giant vortex. Such a state is magnetically hysteretic and has been postulated by a recent theory.