Bilayer WSe2 as a natural platform for interlayer exciton condensates in the strong coupling limit

Exciton condensates (ECs) are macroscopic coherent states arising from condensation of electron-hole pairs(1). Bilayer heterostructures, consisting of two-dimensional electron and hole layers separated by a tunnel barrier, provide a versatile platform to realize and study ECs2-4. The tunnel barrier suppresses recombination, yielding long-lived excitons(4-14). However, this separation also reduces interlayer Coulomb interactions, limiting the exciton binding strength. Here, we report the observation of ECs in naturally occurring 2H-stacked bilayer WSe2. In this system, the intrinsic spin-valley structure suppresses interlayer tunnelling even when the separation is reduced to the atomic limit, providing access to a previously unattainable regime of strong interlayer coupling. Using capacitance spectroscopy, we investigate magneto-ECs, formed when partially filled Landau levels couple between the layers. We find that the strong-coupling ECs show dramatically different behaviour compared with previous reports, including an unanticipated variation of EC robustness with the orbital number, and find evidence for a transition between two types of low-energy charged excitations. Our results provide a demonstration of tuning EC properties by varying the constituent single-particle wavefunctions.

Automated summary

Exciton condensates are macroscopic coherent states formed by the condensation of electron-hole pairs. Bilayer heterostructures provide a platform for studying and realizing exciton condensates, but the separation between layers limits the strength of exciton binding. This study observes exciton condensates in naturally occurring bilayer WSe2 and investigates their properties using capacitance spectroscopy.