Moire trions in MoSe2/WSe2 heterobilayers

Transition metal dichalcogenide moire bilayers with spatially periodic potentials have emerged as a highly tunable platform for studying both electronic(1-6) and excitonic(4,7-13) phenomena. The power of these systems lies in the combination of strong Coulomb interactions with the capability of controlling the charge number in a moire potential trap. Electronically, exotic charge orders at both integer and fractional fillings have been discovered(2,5). However, the impact of charging effects on excitons trapped in moire potentials is poorly understood. Here, we report the observation of moire trions and their doping-dependent photoluminescence polarization in H-stacked MoSe2/WSe2 heterobilayers. We find that as moire traps are filled with either electrons or holes, new sets of interlayer exciton photoluminescence peaks with narrow linewidths emerge about 7 meV below the energy of the neutral moire excitons. Circularly polarized photoluminescence reveals switching from co-circular to cross-circular polarizations as moire excitons go from being negatively charged and neutral to positively charged. This switching results from the competition between valley-flip and spin-flip energy relaxation pathways of photo-excited electrons during interlayer trion formation. Our results offer a starting point for engineering both bosonic and fermionic many-body effects based on moire excitons(14).