Attractive interactions, molecular complexes, and polarons in coupled dipolar exciton fluids

Abstract

Dipolar (or spatially indirect) excitons (IXs) in semiconductor double quantum well (DQW) subjected to an electric field are neutral species with a dipole moment oriented perpendicular to the DQW plane. Here, we theoretically study interactions between IXs in stacked DQW bilayers, where the dipolar coupling can be either attractive or repulsive depending on the relative positions of the particles. By using microscopic band structure calculations to determine the electronic states forming the excitons, we show that the attractive dipolar interaction between stacked IXs deforms their electronic wave function, thereby increasing the inter-DQW interaction energy and making the IX even more electrically polarizable. Many-particle interaction effects are addressed by considering the coupling between a single IX in one of the DQWs to a cloud of IXs in the other DQW, which is modeled either as a closed-packed lattice or as a continuum IX fluid. We find that the lattice model yields IX interlayer binding energies decreasing with increasing lattice density. This behavior is due to the dominating role of the intra-DQW dipolar repulsion, which prevents more than one exciton from entering the attractive region of the inter-DQW coupling. Finally, both models shows that the single IX distorts the distribution of IXs in the adjacent DQW, thus inducing the formation of an IX dipolar polaron di-polaron. While the interlayer binding energy reduces with IX density for lattice di-polarons, the continuous polaron model predicts a non-monotonous dependence on density in semi-quantitative agreement with a recent experimental study [cf. Hubert et al., Phys. Rev. X9, 021026 (2019)].

Confinement of long-lived interlayer excitons in WS$_2$/WSe$_2$ heterostructures

“…Atomic realizations of dipolar ensembles include Rydberg atoms [16][17][18], ultracold polar molecules [19][20][21] and high magneticmoment atoms [22][23][24][25][26]. For semiconductors, long-range interactions can be achieved via spatially indirect excitons, where electrons and holes have finite separation [27,28] yielding a permanent electric dipole moment [29][30][31]. Most progress in realizing such states has been in AlGaAs/GaAs double quantum wells [30,[32][33][34][35], while heterostructures of transition metal dichalcogenide (TMD) monolayers [36] have recently emerged as a promising alternative [37][38][39][40].…”