The unique signatures of an excitonic insulating phase were observed in antimony Sb(110) nanoflakes.
The findings provide a novel strategy to search for more excitonic insulators which is potentially capable of carrying exicton superfluids, and further studies will be required to fully understand the rich physics of this new phase of matter.
"In the 1960s, it was proposed that in small indirect band-gap materials, excitons can spontaneously form because the density of carriers is too low to screen the attractive Coulomb interaction between electrons and holes."
In the insulator family, the first member is the bandgap, 'or 'trivial' insulator.
Besides bandgap insulators, other insulating states may arise through the effects of electron-electron interactions or disorder coupled with quantum interference, for example:
Anderson insulators, in which electrons are localized by quantum interference