Investigating dynamic vortex transitions in 2d superconductors

Extensive molecular dynamics simulations were performed on superconducting samples with periodic square arrays of pinning centers where several strengths, sizes, and densities of the pinning centers were considered. By calculating the average speed of the vortices as the driving force increases, we defined two critical currents that divide the states of the vortices into three different states with respect to the magnitude of the driving current. These vortex states are a pinned state, a disordered flow state where only some of the vortices flow in some vortex channels, and an ordered flow state where all the vortices flow in an ordered and collective manner. We have clarified the roles of the number of vortices, the size, the strength, and the number of pinning centers in these three states at several temperatures.