Speaker
Description
A number of moiré bilayer semiconductors display insulating phases at a filling of one carrier per unit cell ("half-filling"). We understand these insulating states to be driven by strong electronic correlations. It is generally understood that electron screening reduces these correlations, and so these states have been seen in isolated flat band systems. In this work, I will describe recent experiments on twisted double bilayer WSe$_2$, which is an interesting moiré semiconductor that has two separate hole valleys near the zone center and zone boundary. The energy separation between the tops of these valleys can be sensitively controlled using an out of plane electric field. It is thus possible to realize situations where one of the valleys is half-filled, while the other valley has some arbitrary filling. We show that it is possible to have an insulating state formed in one valley while the other continues to remain itinerant - ie, to realize a valley-selective correlated insulator.