Imaging the structure of the domain wall between symmetries   interconnected by a discontinuous transition
  We have been able to observe with single particle resolution the interface between two structural symmetries that cannot be interconnected by a continuous transition. By means of an engineered 2D potential that pins the extremity of vortex strings an square symmetry was imposed at the surface of a 3D vortex solid. Using the Bitter decoration technique and on account of the continuous vortex symmetry we visualize how the induced structure transforms along the vortex direction before changing into the expected hexagonal structure at a finite distance from the surface. 
Yanina Fasano, M. De Seta, M. Menghini, H. Pastoriza and F. de la Cruz