Half Full or Half Empty?

Excitons--that is, pairings of electrons with holes in a semiconductor--are examples of quantum particles called bosons. Like other bosons, such as those studied in ultracold atomic vapors, excitons should form under Bose condensation and fall into a single quantum state. In his Perspective, Eisenstein discusses recent efforts to observe excitonic Bose condensation in layered materials. The major obstacle has been the tendency of the electron and the hole to simply recombine and disappear. By applying a magnetic field, however, the excitons can be stabilized, leading to increased hopes that a clear case of condensation will eventually be observed.