2D excitonic insulators

Excitonic insulators are novel material systems exhibiting correlated electronic phases. Condensation of excitons to its ground state happens for a specific condition when the exciton binding energy (Eb) is larger than the band gap (Eg). The excitonic condensation in semiconductors occurs through a Bose-Einstein condensation process, while the condensation in semimetals occurs through the Bardeen-Cooper-Schrieffer (BCS) process.  The spontaneous band hybridization caused by the Coulomb attraction between the orthogonal conduction (electron) and valence (hole) bands opens the bandgap and drives the system into the insulating state