Dipolar Attraction and Repulsion Between Indirect Excitons

We examine the attractive and repulsive dipolar interaction between indirect excitons (IXs) formed by electrons and holes in separated layers. Repulsive dipolar IX interactions have been studied thoroughly in the past but attractive interaction have yet to be similarly explored. Each layer of IXs forms in a single pair of couple quantum wells (CQW) where the out-of-plane IX electric dipoles lead to the repulsive interaction between IXs. The attractive interaction appears between IXs in different IX layers created in 2-CQW heterostructures with 2 layers of IX dipoles. In both experimental measurements and theoretical simulations, we found that increasing the density of IXs in one layer causes a monotonic energy reduction for IXs in the other layer. Additionally, we found an in-plane shift of a cloud of IXs in one layer toward a cloud of IXs in the other layer. This behavior is qualitatively consistent with attractive dipolar interaction. The measured IX energy reduction and IX cloud shifts are higher than the values given by the correlated liquid theory.