Interlayer Excitons in van der Waals Heterostructures in a Magnetic Field*

We investigate particle-hole excitations in bilayer 2D van der Waals heterostructures in a magnetic field. Such systems are interesting because the two constituents of the excitons can reside in band environments of very different Berry’s curvatures. This allows the neutral excitations to carry signatures of the fermionic electronic structures of the individual materials. Moreover, the heterostructures can give rise to a large moiré unit cell. The effective periodicity relaxes momentum conservation so that the exciton dispersion at finite momentum could be detected by light absorption. As an example, we study an MoS₂-graphene heterostructure, for which both valleys host Berry’s curvature in only one layer. We consider variational single particle-hole pair wavefunctions, both in terms of the Landau levels and eigenstates of magnetic translation operators. The formalism allows one to identify how wavefunction overlaps determine the exciton state and energy. We show for this heterostructure that the energy disperses remarkably slowly. The impacts of many-body effects and the quasi-periodic tunneling between the layers associated with the moiré pattern on exciton dispersions and light absorption are also considered.