Magnetic-field-driven localization of light in a cold-atom gas
  We discover a transition from extended to localized quasi-modes for light in a gas of immobile two-level atoms in a magnetic field. The transition takes place either upon increasing the number density of atoms in a strong field or upon increasing the field at a high enough density. It has many characteristic features of a disorder-driven (Anderson) transition but is strongly influenced by near-field interactions between atoms and the anisotropy of the atomic medium induced by the magnetic field. 
S.E. Skipetrov and I.M. Sokolov
physics.optics cond-mat.quant-gas physics.atom-ph