Spontaneous Bose-Einstein condensation of excitons

Excitons are pairs of electrons and holes inside a solid material that together behave like a single particle. It has long been suspected that when many such excitons exist in the same piece of matter, they can form a single giant quantum state called a Bose-Einstein condensate - the same process which is responsible for a metal losing all its electrical resistance when it becomes a superconductor, for example. However, actually proving that Bose-Einstein condensation of excitons occurs in any r...