Dumping Topological Charges on Neighbors: Ice Manifolds for Colloids and   Vortices
  We investigate the recently reported analogies between pinned vortices in nano-structured superconductors or colloids in optical traps, and spin ice materials. The frustration of colloids and vortices differs essentially from spin ice. However, their effective energetics is made identical by the contribution of an emergent field associated to the topological charge, thus leading to a (quasi) ice manifold for lattices of even (odd) coordination. The equivalence extends to the local low-energy dynamics of the ice manifold, where the effect of geometric hard constraints can be subsumed into the spatial modulation of the emergent field, which mediates an entropic interaction between topological charges. There, as in spin ice materials, genuine ice manifolds enter a Coulomb phase, whereas quasi-ice manifolds posses a well defined screening length, provided by a plasma of embedded topological charges. The equivalence between the two systems breaks down in lattices of mixed coordination because of topological charge transfer between sub-latices. We discuss extensions to social and economical networks. 
Cristiano Nisoli
cond-mat.stat-mech