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 (dipolaron). While the interlayer binding energy reduces with IX density for lattice dipolarons, the continuous polaron model predicts a nonmonotonous dependence on density in semiquantitative agreement with a recent experimental study [cf. Hubert et al., Phys. Rev. X 9, 021026 (2019)].
Physical Review B
We thank W. Kaganer for discussions and for comment on the manuscript. We acknowledge the financial support from the German-Israeli Foundation (GIF), grant agreement I-1277-303.10/2014. M.L. acknowledges support by the Austrian Science Fund (FWF), under project No. P29902-N27, and by the European Research Council (ERC) Starting Grant No. 801770 (ANGULON). A.G. acknowledges support by the European Unions Horizon 2020 research and innovation program under the Marie Skodowska-Curie grant agreement No 754411. P.V.S acknowledges financial support from the Deutsche Forschungsgemeinschaft (DFG) under Project No. SA 598/12-1.
Hubert C, Cohen K, Ghazaryan A, Lemeshko M, Rapaport R, Santos PV. Attractive interactions, molecular complexes, and polarons in coupled dipolar exciton fluids. Physical Review B. 2020;102(4). doi:10.1103/physrevb.102.045307
Hubert, C., Cohen, K., Ghazaryan, A., Lemeshko, M., Rapaport, R., & Santos, P. V. (2020). Attractive interactions, molecular complexes, and polarons in coupled dipolar exciton fluids. Physical Review B. American Physical Society. https://doi.org/10.1103/physrevb.102.045307
Hubert, C., K. Cohen, Areg Ghazaryan, Mikhail Lemeshko, R. Rapaport, and P. V. Santos. “Attractive Interactions, Molecular Complexes, and Polarons in Coupled Dipolar Exciton Fluids.” Physical Review B. American Physical Society, 2020. https://doi.org/10.1103/physrevb.102.045307.
C. Hubert, K. Cohen, A. Ghazaryan, M. Lemeshko, R. Rapaport, and P. V. Santos, “Attractive interactions, molecular complexes, and polarons in coupled dipolar exciton fluids,” Physical Review B, vol. 102, no. 4. American Physical Society, 2020.
Hubert C, Cohen K, Ghazaryan A, Lemeshko M, Rapaport R, Santos PV. 2020. Attractive interactions, molecular complexes, and polarons in coupled dipolar exciton fluids. Physical Review B. 102(4), 045307.
Hubert, C., et al. “Attractive Interactions, Molecular Complexes, and Polarons in Coupled Dipolar Exciton Fluids.” Physical Review B, vol. 102, no. 4, 045307, American Physical Society, 2020, doi:10.1103/physrevb.102.045307.