Nucleation of multiquantum flux bundles in a type I superconducting strip in a perpendicular magnetic field

With real-time flux read-out (in the microsecond range) one can separate reversible from irreversible flux penetration into a superconducting strip submitted to a perpendicular increasing magnetic field. This allows a non-ambiguous definition of three regimes of flux penetration. As usual, the irreversible regime is associated with the presence of an energy barrier. By comparing our experiments with magneto-optical observations, we establish that the range over which the flux irreversibly penetrates is indeed controlled by the existence of diamagnetic zones between the edges of the strip and the central intermediate state.