Modeling the Shape and Clarifying the Condition of a Moving S-N Border During Pulsed S-N Switching of YBCO Thin Films

Transition from the superconducting (S) to the normal (N) state in YBCO thin films (S-N switching) induced by nanosecond current pulses has been studied extensively. Still, the properties of the moving S-N border during N zone propagation have not yet been identified. This paper continues a theoretical and descriptive study aimed at modeling the real shape and condition of the moving border. The bent shape of the border is caused by the opposition between the Meissner and Lorentz forces. The equilibrium of these forces leads to bifurcations and the buckling of valleys. To better understand the dynamic changes in the border, we present two additional local propagation developments preceded by bifurcation and subsequent reconnection of the border’s S currents. The incompressibility of the Meissner currents intricately alters the border’s shape. Its other properties such as extreme flexibility and high tensile strength allow us to present its quasi-real fractalized form. The phase transition and the heat replenishing the energy loss ahead of the border indicate ultrafast N zone propagation exhibiting combustion wave properties. The discussion substantiates that during propagation, the S-N border is in a condition of constantly being in an unstable state, resembling a magnetohydrodynamic (MHD) Richtmyer–Meshkov instability.