Flux turbulence in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ single crystals

We present magneto-optical imaging studies of flux turbulence in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ single crystals. When magnetic flux is trapped by pinning in a Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ single crystal and a moderate field of reverse direction is subsequently applied, a boundary of zero flux density will divide the regions of flux and antiflux. The propagation of this boundary shows turbulent behavior in narrow temperature ranges around 25 K. This is the first time that the flux turbulence is observed in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ single crystals. In addition, the flux turbulence was found to be strongly correlated with the second-peak flux penetration. The implication of this study to the available theoretical models will be discussed.