  Highly customizable interfaces created by van der Waals stacked 2D materials
provide an extremely flexible opportunity for engineering and effectively
controlling material properties. The atomic-thin nature and strong scalability
of transition metal dichalcogenides (TMDs), the star family of two-dimensional
semiconducting materials, allow for the modulation of their inherent optical
and electrical characteristics by utilizing various environmental stimuli. In
such a material system, the stacking mechanism with spatial separation in the
structure enables recent observations of dipolar many-body complexes with the
interplay of multi-particles, leading to some exotic and novel excitonic
phenomena and enabling the closer study of high-correlated quantum physics. The
presence of powerful dipole-dipole interactions among long-lived interlayer
excitons can cause the system to enter unique classical and quantum phases with
multiparticle correlations, such as dipolar liquids, dipolar crystals and
superfluids. The strong binding energy of interlayer excitons in TMD-based
hetero-bilayers especially enhances the critical temperature of these exotic
phenomena. Here, we provide a concise summary of the recent frontier research
progress on dipolar complexes and many-body effects in TMD double layers,
encompassing fundamental theory and properties modulation. We reveal the
significance and current challenges of this research field and present the
potential developing directions of the hetero-bilayers in quantum physics and
quantum devices by adding new levels of external control or integration.
