Detailed look into the unstable S-N border during propagation of the N-zone into the thin YBaCuO film

Abstract

The focus is on the initial processes which change the shape of the bending S-N border during pulsed electrical S-N switching of thin YBaCuO films. These processes were noted on the SEM images of damaged films. The YBaCuO strip samples of high critical current densities were damaged by overcritical current pulses of nanosecond duration. The processes obtain different properties depending on the effective penetration length that the films have. During the N-zone propagation by the channel, led by the top unstable S-N border, an iterative transformation of the S-N border shape takes place. Two sets of the processes at the single transformation step, demonstrating weak and strong coherent jets action, are visualized and described. The origin of coherent jet formation, which is the driving force of the processes, is discussed. A peculiar interpretation of the moving top of the N-zone as a band in the state of Richtmayer-Meshkov instability is also proposed. It appears that devices with elements of the micro-scale dimensions should manifest the ultra-high speed of the S-N switching.