Rotational transition, domain formation, dislocations and defects in vortex systems with combined six- and 12-fold anisotropic interactions*

We introduce a new model for a pairwise repulsive interaction potential of vortices in a type-II superconductor, consisting of superimposed six- and 12-fold anisotropies. Using numerical simulations we study how the vortex lattice configuration varies as the magnitudes of the two anisotropic interaction terms change. A triangular lattice appears for all values, and rotates through 30° as the ratio of the six- and 12-fold anisotropy amplitudes is varied. The transition causes the VL to split into domains that have rotated clockwise or counter-clockwise, with grain boundaries that are "decorated" by dislocations consisting of five- and seven-fold coordinated vortices. We also find intra-domain dislocations and defects, and characterize them in terms of their energy cost.