Creating and tuning of interlayer exciton gases in transition metal dichalcogenides heterostructures

Stacking two-dimensional materials into van der Waals heterostructure offers a powerful approach toward creating artificial lattices with desired band structures and functionalities. In transition metal dichalcogenides heterostructures, interlayer exciton emerges due to band alignment of constituent layers and has been demonstrated to have long exciton lifetime [1] and valley lifetime [2], providing a platform to study degenerate Boson gases, rich valley physics, and possible optoelectronics applications. Here we report highly tunable interlayer excitons by an out-of-plane electric field in homobilayer WSe₂. Electric field can tune the interlayer exciton dipole orientation from negative to positive and induce a Stark shift of up to 100meV in the exciton resonance energy. Moreover, with applied electric field, the exciton lifetime is greatly enhanced by more than two orders of magnitude (from ~200ps to >20ns), allowing the creation of interlayer exciton gas with density as high as 1.2x10¹¹cm^-2 by moderate continuous-wave optical pumping. Furthermore, we can achieve high interlayer exciton density (~10¹²cm^-2) with a trilayer heterostructure by both optical pumping and electrical injection.
[1] Nat. Commun. 6, 6242 (2015).
[2] Sci. Adv. 3, (2017).