Organic-2D material heterostructures: A promising platform for Excitonic Bose-Einstein Condensation

The exotic state of Bose-Einstein condensation (BEC), generally observed at extremely low temperatures, occurs when all the bosons in the system occupy the ground state. Due to their smaller bosonic mass compared to atoms, Excitons, which are bound electron hole pairs generated in matter by the absorption of photons, can undergo BEC at higher temperatures. However, these excitons need to have long lifetimes, high densities, and small exciton momenta, in order to undergo BEC. While experiments on MoSe2/WSe2 bilayers exhibit excitonic BEC at high temperatures of ~100 K, precise alignment of the layers is required to maintain coherence and hence BEC [1]. Here, we predict that the lowest energy charge transfer excitons in ZnPc-MoS2 organic-2D material heterostructures are ideal candidates for BEC, using first principles GW-BSE calculations [2]. The lowest energy charge transfer excitons in these heterostructures arise from direct transitions, are strongly bound (localized in ~1-2 nm) and have long lifetimes of the order of nanoseconds, and achieving BEC transition temperatures of ~50-100 K.

References:

[1] Mak et al., “Evidence of high-temperature exciton condensation in two-dimensional atomic double layers”, Nature 2019, 574, 76.

[2] K. Ulman and S. Y. Quek, “Organic-2D Material heterostructures: A Promising Platform for Exciton Condensation and Multiplication”, Nano Letters 2021, 21, 8888.