Dynamics of vortices in type-II superconductors with periodic square columnar pins

Abstract

The dynamics of a two-dimensional vortex system with strong periodic square columnar pins is investigated. For the case vortex number matching pinning number, we find that the vortex liquid is frozen into square lattice via a continuous transition, and the freezing (melting) temperature T m is the same as the thermal depinning temperature of vortices, which are different from the first-order phase transition at weak pinning. The zero-temperature critical depinning force F c0 is exactly the same as the maximum pinning force, and the depinning property at T = 0 can be expressed by scaling v ∼ ( F − F c0 ) β with the exponent β close to 0.5. The v– F curves at temperatures below T m show that vortices are pinned at small driving force.