Transient vortex states in Bi₂Sr₂CaCu₂O_8+δ crystals

A high temporal resolution magneto-optical system is employed to observe the time evolution of the vortex structure in Bi₂Sr₂CaCu₂O_8+δ crystals after a sudden application of a magnetic field. The magneto-optical images reveal dynamic coexistence of two vortex phases: a quasiordered phase in the sample interior and a transient disordered phase near the sample edges. The border between these two phases, marked by an abrupt change in the gradient of the local induction, moves with time. This motion enables tracing the decay of the transient state and the concurrent growth of the thermodynamic vortex phases. The growth rate is sensitive to the location in the field-temperature phase diagram.