Real-space imaging of structural transitions in the vortex lattice of V3Si

The predictions of nonlocal London theory are confirmed by real-space measurements of the hexagonal-to-square transition in the vortex lattice structure of V₃Si. We observe that the lattice transforms from hexagonal to nearly square over the field range of 0–4 T for fields applied along the [001] direction. Above ≈0.75 T, we find that the lattice orientation is strongly linked to the symmetry of the underlying V₃Si crystal and has a (100) symmetry plane. Near the rhombus-to-square transition at 4 T, we observe anisotropic long-range translational order, consistent with predictions of the elasticity of the lattice near this transition.