Hierarchical structure formation in layered superconducting systems with   multi-scale inter-vortex interactions
  We demonstrate formation of hierarchical structures in two-dimensional systems with multiple length scales in the inter-particle interaction. These include states such as clusters of clusters, concentric rings, clusters inside a ring, and stripes in a cluster. We propose to realize such systems in vortex matter (where a vortex is mapped onto a particle with multi-scale interactions) in layered superconducting systems with varying inter-layer thicknesses and different layer materials. 
Christopher N. Varney, Karl A. H. Sellin, Qingze Wang, Hans Fangohr,   and Egor Babaev
cond-mat.supr-con cond-mat.mes-hall