Richen Xiong

Abstract The emergence of charge-neutral collective modes is a hallmark of correlated quantum phases but is often challenging to probe. In two-dimensional flatband systems, charge responses have been intensively investigated, but neutral excitations have not been directly probed. In particular, the intervalley-coherent state has been proposed as a unifying theme across graphene- and semiconductor-based systems and features a neutral Goldstone mode due to spontaneously broken valley U(1) symmetry.

Abstract A panoply of unconventional electronic states has been observed in moiré superlattices. Engineering similar bosonic phases remains, however, largely unexplored. We report the observation of a bosonic correlated insulator in WSe2/WS2 moiré superlattices composed of excitons, i.e., tightly bound electron-hole pairs.