Domain Boundary Dissolution of Six and Twelve-fold Anisotropic Vortex Lattices

When superconductors are exposed to a magnetic field, it penetrates the material in the form of quantized vortices. These vortices are repulsive and, will organize themselves into an ordered lattice with a symmetry and orientation that depend on the form of their interaction potential. One such potential, manifested in the two-band superconductor MgB2, is a combined 6 and 12 fold anisotropy which produces a triangular lattice with various orientations based on the ratio of the two anisotropic terms. Here, a large ratio resulting in two distinct domains of vortices and a low ratio forming a single domain. We have investigated the phase transition between the two domain ordering to the single domain using a molecular dynamics simulation. It was found that the system does not evolve completely by only changing the aforementioned ratio, but requires the application of additional perturbation through oscillating the effective density of the vortices which facilitates the phase transition and reduces the difference in the relative angle of the two domains logarithmically with respect to time. This is in agreement with small-angle neutron scattering studies carried out by our group [Louden et al., Phys. Rev. B 99,144515 (2019)].