Self-organized structure of vortex droplets inBi2Sr2CaCu2O8single crystals induced by ac magnetic field

Abstract

In the paper [L. S. Uspenskaya and A. L. Rakhmanov, Phys. Rev. Lett. 100, 137002 (2008)] we reported the magneto-optic observation of droplets of vortex matter in ${\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8}$ single crystals pumped by the low-frequency ac magnetic field. This self-organized structure grows along planar defects in the temperature range $12<T<30\text{ }\text{K}$. The droplet arises at some ``weak'' point in the defect, grows with number of periods of the ac field, ``blows up,'' and shifts along the defect. Then, the next droplet arises at the same point. Here we present a detailed description of the phenomenon. In addition, we study evolution and relaxation of the droplets. The observed effect is interpreted in terms of the magnetic flux dynamics in the superconductor accounting for the energy of stray magnetic fields.