Interlayer exciton phase diagram in atomically thin heterostructures

Interlayer excitons (IEs), bound electron-hole pairs, are optical excitations that can display rich phenomena such as superfluidity. In atomically thin semiconductor heterostructures, IEs exhibit remarkable electrical tunability due to their permanent out-of-plane dipole moments, enabling the design of optoelectronic excitonic devices. Here, we modulate the IE spatial distribution and control the electron-hole pair density via electrostatic gating. At high densities, we observe an exponential linewidth broadening that we interpret as the exciton-to-plasma ionization transition. The threshold density is independent of the applied electric field, and remains constant below 20 K. At higher temperatures, the critical density increases, consistent with a quantum degenerate ground state of IEs. With a new understanding of the IE phase diagram, we discuss the next steps towards attaining excitonic condensates on two-dimensional material platforms.

Associated work: A. Y. Joe^*, A. M. Mier Valdivia^* et al. “Controlled interlayer exciton ionization in an electrostatic trap in atomically thin heterostructures”. Nat. Commun. 15: 6743 (2024)