Strongly correlated electronic states and dielectric engineering in heterobilayer, heterotrilayer and bilayer-bilayer MoSe₂/WSe₂ heterostructures

Moiré heterostructures formed from twisted layers of transition metal dichalcogenides (TMDs) have been shown to host strongly correlated states including Mott insulators and Wigner crystals. However, experimental investigations have been mostly limited to two stacked monolayers. Here we use white light reflection spectroscopy to investigate the intralayer excitons in a unique device of stacked WSe₂/MoSe₂ where there are 1L/1L, 2L/1L, 1L/2L and 2L/2L regions with the same twist angle (~57 degrees).  Changing the carrier concentration we compare the correlated electron and hole states formed in each region. We observe, relative to the 1L/1L heterobilayer, correlations are suppressed in heterostructures using 2L MoSe₂, while they are enhanced using 2L WSe₂. Due to different dielectric environments we also observe an energetic splitting of the intralayer excitons localised in seperate layers of the bilayers. In 2L WSe₂/1L MoSe₂ we probe the effects of the correlated electronic insulating phases on each layer-localised exciton and find larger changes to the peak position and linewidth in the layer adjacent to the heterostructure interface. Our results introduce layer thickness as a new tuning knob for the formation of correlated electronic states in TMD moiré heterostructures.