Numerical simulation and experimental observation of magnetic flux distribution in high-temperature superconductors

A new procedure for the minimization of the free energy potential by means of Monte Carlo techniques has been used to calculate the equilibrium configurations of vortices inside the superconducting plate with pinning centres. The pictures of the magnetic flux distribution were obtained for cyclical changes of the external magnetic field at different temperatures and defective states of the superconductor. A sharp zone of zero magnetic field was found to exist between the regions of magnetic fields with opposite sign. It was shown that the zero field zone moves from the edges to the centre of the superconductor when the external field changes. We called this phenomenon 'annihilation waves'. The peculiarities of annihilation waves at different temperatures and defects concentrations have been investigated. The maps of the magnetic field distribution as well as the motion of the annihilation waves correlate well with the static and dynamic images which were observed in the our recent magneto-optical and scanning Hall sensor experiments. (author)