Instability of vortex-antivortex interface in optimally-doped   Ba(Fe_{1-x}Co_{x})_{2}As_{2}
  We explore the flux front patterns during virgin penetration and after remagnetization in the iron-based superconductor Ba(Fe_{1-x}Co_{x})_{2}As_{2}. After remagnetization we observe an instability characterized by turbulent dynamics at the vortex-antivortex boundary. Associated with the turbulent flux boundary a band of excess current density is observed. The turbulence is contrasted with the instability observed in the cuprate superconductors. Our results suggest turbulent instability at the vortex-antivortex interface may be a common feature in all remagnetized type-II superconductors. 
Shyam Mohan, Yuji Tsuchiya, Yasuyuki Nakajima, Tsuyoshi Tamegai
cond-mat.supr-con