Flux Line Lattices in Artificially Layered Superconductors

The flux line lattice of superconductors has been investigated when there exists a periodicity in the underlying system, such as can occur in artificially layered structures. For small fields parallel to the layers the flux lines enter the sample in sequential rows, with the possibility of jumps in the magnetization as new rows are created. As the field is increased these discontinuities gradually decrease, but there still exist transitions between states that are aligned differently to the periodic direction. Increasing the magnitude of the periodic potential reduces the competition between differently aligned lattices and tends to lock in one particular alignment. The effect of transitions on the shear modulus is also discussed and related to the experiments of Theunissen et al.