Thickness and twist angle tunable moiré excitons in InSe/GaSe heterostructures*

Moiré quantum systems have emerged as a materials framework displaying highly tunable electronic, optical and topological properties with an exquisite level of control. To date, the moiré physics has been constrained mainly by two factors i) the dimensionality, defined by the stacking of monolayers, and ii) the twist angle φ, which unveils novel phases only at quite precise values (e.g. superconductivity, orbital magnetism, correlated insulator states). Here, we overcome these practical limitations through a new class of heterostructures composed of γ-InSe on ε-GaSe that reveal strong evidence for the moiré potential even in thick stacked layers and at arbitrary values of φ. We detect a pronounced interlayer exciton composed of several superimposed emissions that are uniformly spaced in energy ΔE  with pronounced φ-dependence. In the interfacial area, similar behavior is displayed also by the intralayer exciton of GaSe. This strong correlation between φ and ΔE implies the localization of excitations at the moiré potential minima. But in contrast to transition metal dichalcogenides (TMDs), the moiré potential modulates the multi-component interlayer exciton over the entire range of φ due to their direct band-gap at the center of their Brillouin zone. γ-InSe/ε-GaSe interfaces offer an unprecedented level of moiré exciton tunability not yet achieved in any other van der Waals heterostructure. Our results demonstrate clear pathways for quantum optoelectronics while offering opportunities to study electronic correlations over a broad range of moiré periodicities and layer thicknesses.