Moir\'e excitons in MoSe$_2$-WSe$_2$ heterobilayers and heterotrilayers.

We report experimental and theoretical studies of excitons in twisted stacks of MoSe$_2$-WSe$_2$ heterobilayers and heterotrilayers. We observe distinct optical signatures for the heterobilayer and heterotrilayer regions of a MoSe$_2$-WSe$_2$ heterostack, and interpret our experimental findings in the framework of moir\'e modulated momentum direct and indirect interlayer excitons. Our results highlight the role of interlayer hybridization for exciton relaxation and formation in multi-layered semiconductor van der Waals heterostructures.