First vortex entry into a perpendicularly magnetized superconducting thin film

Abstract

In type-II superconductors, the flux-free state (Meissner state) may be invaded by vortices bearing quantized flux once $H$ is above the lower critical field ${H}_{c1}$. However, the actual first flux penetration does not occur at ${H}_{c1}$ due to the presence of a surface barrier and the fact that the Meissner state may also exist as a metastable state up to a larger (superheating) field. In this work we determine the field for the first vortex penetration in superconductors by directly imaging the first vortex threading a superconducting Pb film with antidots. We find that the first vortex penetration occurs when the surface superconducting currents reach the depairing current, locally breaking superconductivity and allowing a vortex to nucleate.