Monolayer excitonic insulator

According to electronic band structure calculations, monolayer 1T’-WTe2 is a topological semi-metal, in which electron and hole pockets of the two-dimensional bulk cross the Fermi level. On the other hand, electron transport experiments on this material reveal quantized conduction along the one-dimensional topological edge states, suggesting the presence of an electrically insulating monolayer bulk. We combined electrical transport with scanning tunneling microscopy experiments to solve this riddle. In our recent arXiv posting we argue that the attractive interaction between electrons and holes in the semi-metallic monolayer engenders an excitonic insulator phase with gapped electronic states at the Fermi level. Check it out!