The instability of the vortex antivortex system in hard superconductors

L.M. Fisher1, A. Rakhmanov2, V. Yampol'skii3, P.E. Goa4, 
M. Baziljevich4, T.H. Johansen4

1 All-Russian Electrical Engineering Institute, Moscow, Russian Federation
2 Institute for Theoretical and Applied Electrodynamics, Moscow, Russian Federation
3 Institute for Radiophysics and Electronics NASU, Kharkov 61085, Ukraine
4 Department of Physics, University of Oslo, Norway

The possible mechanism of the macroturbulence instability observed in fluxline systems during remagnetization of superconductors is proposed. It is shown that when a region with flux is invaded by antiflux the interface can become unstable if there is a relative tangential flux motion. This condition occurs at the interface owing to the anisotropy of the viscous motion of vortices. The phenomenon is similar to the instability of the tangential discontinuity in classical hydrodynamics. The obtained results are supported by magneto-optical observations of flux distribution on the surface of a YBCO single crystal with twins