Dipole-dipole interactions between localized interlayer excitons in WSe₂/MoSe₂ heterobilayer

We explored localized interlayer excitons in WSe₂/MoSe₂ heterobilayer by low temperature (~ 4K) photoluminescence spectroscopy. With type-II band alignment, the localized interlayer exciton compromises of an electron from MoSe₂ and a hole from WSe₂, forming an out-of-plane electric dipole moment. We thus tuned its energy by hundreds of its linewidth via an external electric field. In addition to the field-tuneability, the permanent dipoles have repulsive dipolar interaction scaled as ~ 1/r_ex³ where r_ex is the interexcitonic distance. Here we observed a peak blueshifted from the localized interlayer exciton peak by ~ 2 meV with increasing incident power. The blue peak is assigned to be the biexciton peak due to the same synchronized jittering as the exciton and its superlinear power dependence. The similar g factor and gate dependence of biexciton and exciton imply that the second excitation has negligible impact on the exciton wavefunction. The polarization of the biexciton and exciton under finite magnetic field is consistent with the spin-valley singlet nature of the dipolar molecule states. With the singlet configuration and dipolar interaction ~ 2 meV, the confinement length of the localized interlayer exciton is calculated to be ~ 5 nm.