Abstract
Due to a strong Coulomb interaction, excitons dominate the excitation kinetics in 2D materials. While Coulomb-scattering between electrons has been well studied, the interaction of excitons is more challenging and remains to be explored. As neutral composite bosons consisting of electrons and holes, excitons show a non-trivial scattering dynamics. Here, we study on microscopic footing exciton-exciton interaction in transition-metal dichalcogenides and related van der Waals heterostructures. We demonstrate that the crucial criterion for efficient scattering is a large electron/hole mass asymmetry giving rise to internal charge inhomogeneities of excitons and emphasizing their cobosonic substructure. Furthermore, both exchange and direct exciton-exciton interactions are boosted by enhanced exciton Bohr radii. We also predict an unexpected temperature dependence that is usually associated to phonon-driven scattering and we reveal an orders of magnitude stronger interaction of interlayer excitons due to their permanent dipole moment. The developed approach can be generalized to arbitrary material systems and will help to study strongly correlated exciton systems, such as moire super lattices.
Highlights
We predict an unexpected temperature dependence that is usually associated with phonon-driven scattering, and we reveal an orders of magnitude stronger interaction of interlayer excitons due to their permanent dipole moment
The emergence of atomically thin two-dimensional (2D) materials, such as graphene and monolayer transition metal dichalcogenides (TMDs), has initiated a new research field offering a platform for the investigation of many-body correlations and quantum phenomena [1,2,3,4]
We investigate exciton-exciton scattering in TMD monolayers and van der Waals heterostructures based on a microscopic and quantum-mechanic approach
Summary
The emergence of atomically thin two-dimensional (2D) materials, such as graphene and monolayer transition metal dichalcogenides (TMDs), has initiated a new research field offering a platform for the investigation of many-body correlations and quantum phenomena [1,2,3,4]. While scattering between electrons has been treated extensively in literature [26,27], a microscopic treatment of the Coulomb interaction of excitons as neutral cobosonic quasiparticles has proven to be challenging [28,29,30]. We reveal an intriguing temperature and screening dependence of EID and provide microscopic insights into the fundamental nature of scattering between intralayer and interlayer excitons. The latter exhibit a permanent out-of-plane dipole moment, and their interaction can be considered as an efficient dipoledipole coupling [Fig. 1(a)] resulting in an EID in the range of a few meV. The gained microscopic insights are applicable to a broader class of excitonic, multi-valley materials
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