Bilayer WSe$_2$ as a natural platform for interlayer exciton condensates in the strong coupling limit

TL;DR

This paper reports the observation of interlayer exciton condensates in naturally stacked bilayer WSe$_2$, revealing strong interlayer coupling effects and tunable properties via wavefunction manipulation, advancing understanding of excitonic quantum states.

Contribution

It demonstrates the realization of exciton condensates in 2H-stacked bilayer WSe$_2$ with strong coupling, highlighting the role of intrinsic spin-valley structure in suppressing tunneling and enabling new regimes.

Findings

Observation of exciton condensates in bilayer WSe$_2$

Identification of a transition between two types of low-energy charged excitations

Evidence of tunable exciton properties through wavefunction variation

Abstract

Exciton condensates (EC) are macroscopic coherent states arising from condensation of electron-hole pairs. Bilayer heterostructures, consisting of two-dimensional electron and hole layers separated by a tunnel barrier, provide a versatile platform to realize and study EC. The tunnel barrier suppresses recombination yielding long-lived excitons. However, this separation also reduces interlayer Coulomb interactions, limiting the exciton binding strength. Here, we report the observation of EC in naturally occurring 2H-stacked bilayer WSe$_2$. In this system, the intrinsic spin-valley structure suppresses interlayer tunneling 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-EC, formed when partially filled Landau levels (LL) couple between the layers. We find that the strong-coupling EC show dramatically different behaviour compared with previous reports, including an unanticipated variation of the 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.