"Engineering the Nanoscale via Modification of the Local Energy Environment for Excitons"

Van der Waals (vdW) 2D heterostructures are a promising platform for harnessing interlayer excitons (IXs). Typically, moiré superlattices in twisted 2D/2D heterostructures create a periodic energy landscape for IXs. This study presents an alternative method for creating a superlattice potential using a periodic array of "up" and "down" molecular dipoles. Our approach involves growing a few layers of titanyl phthalocyanine (TiOPc) molecules on a monolayer of molybdenum disulfide (MoS₂) through vdW epitaxy. Angle-resolved photoemission (ARPES) measurements indicate band narrowing in MoS₂ after molecule deposition. Moreover, time-resolved two-photon photoemission spectroscopy (TR-TPPE) reveals two long-lived IX states with an energy difference of approximately 0.1 eV, attributed to IX’s localization at "up" and "down" dipole sites. Density functional theory calculations indicate that this energy difference is consistent with the electrostatic potential modulation induced by the TiOPc bilayer. Because the symmetry and the period of this potential superlattice can be changed readily by using molecules of different shapes and sizes, molecule/2D heterostructures can be promising platforms for designing artificial exciton and electron lattices, which can be useful for hosting many body phases such as the Bose-Einstein condensate.