Polarization catastrophe in doped cuprates and metal-ammonia solutions. Metal-to-superconductor transition versus phase separation

Abstract
On doping polar dielectrics, such as cuprates (solid) or amonia (liquid), the polarization induces the formation of polarons or solvated electrons. However, the exact role of such entities in the metal-to-insulator transition (MIT) which occurs at some critical densities still remains unclear. We think that their formation together with their long-range Coulomb interactions are responsable for a polarization catastrophe leading to the MIT. Moreover, the accompanishing phenomena is the occurence of a negative sign of the static dielectric constant, which could yield either an insulator-to-superconductor transition in cuprates, either a phase separation in metal-ammonia solutions. The difference of hehavior possibly could come from the nature of the counter ions of the doping charges, which are essentially frozen in oxides, while they remain in a liquid state in metal-ammonia system.