Heterobilayers*

Fabricating moiré superlattices with sufficient uniformity and reproducibility, especially involving transition metal dichalcogenides (TMDs), has been a great challenge, severely hindering the progress of moiré system research. We present an assembly method that addresses this challenge well, and then report new finding on the properties of moiré excitons. By traditional dry transfer method of polycarbonate with specific assembling condition, including ultra-high vacuum and extremely low lamination speed, atomically clean interfaces can be achieved for Van der Waals heterostructures (vdWHs) such as TMD/TMD and TMD/hBN. Presentatively, we assemble atomic-clean monolayer MoSe₂/WSe₂ heterostructure with controlled angle encapsulated by hBN. Measuring by piezoresponse force microscopy, We find distortion of the moiré period is found to be only a few percentages across the sample area of about 5×10 μm². At low temperatures, we observe photoluminescence from the sample with high structural homogeneity. We observe homogeneous moiré exciton emissions across the whole heterostructure. Several samples with different twist angle shows reproductive spectra of moiré exciton. Without complex components enable us to further distribute the spectra of moiré exciton. We find twist-angle independent and dependent component of spectra, which could reveal the physical origin of moiré exciton.