Transition between quadrupole and staggered dipole interlayer excitons inWSe2/MoSe2/WSe2heterotrilayers

Abstract

Recently, a new exciton species of quadrupole exciton (QX) has been discovered in two-dimensional (2D) transition-metal dichalcogenide (TMD) heterotrilayers, which has attracted increasing attention for its fascinating properties. Theoretically, it is predicted that QXs will be squeezed into energetically favored staggered dipole excitons (Stg-DXs) as the exciton density increases. Here, we report photoluminescence spectroscopy studies of this exciton transition between QXs and Stg-DXs in WSe2/MoSe2/WSe2 heterotrilayers. As the exciton density increases, we observe that the Stark effect curve gradually deforms from a hyperbola to a piecewise linear function, providing the first sign of the transition. At the same time, the initially dark QXs become radiative, reaffirming the transition from QXs to Stg-DXs, as the optical selection rules are lifted by breaking the mirror symmetry. Remarkably, we find that this transition can be tuned by introducing doping to change the screening and thus the interactions between excitons. Our results provide observations and understanding of QXs and Stg-DXs in TMD heterotrilayers.