Wigner crystallization in quantum electron bilayers
  The phase diagram of quantum electron bilayers in zero magnetic field is obtained using density functional theory. For large electron densities the system is in the liquid phase, while for smaller densities the liquid may freeze (Wigner crystallization) into four different crystalline phases; the lattice symmetry and the critical density depend on the the inter-layer distance. The phase boundaries between different Wigner crystals consist of both first and second order transitions, depending on the phases involved, and join the freezing curve at three different triple points. 
G. Goldoni(1) and F.M. Peeters(2) ((1) INFM, Dipartimento di Fisica,   Univ. of Modena, Italy (2) Departement Natuurkunde, U...