moiré superlattices

Van der Waals heterobilayers with small twist angles exhibit moiré potentials that not only confine excitons and electrons, but also enhance their mutual interactions. Such strong correlation has been demonstrated for hole-doped WSe₂/WS₂ heterobilayers, as manifested in enhanced antiferromagetic interactions between the correlated holes and excitons. Here, we show such interactions with a ferromagnetic character for electron-doped MoSe₂/WS₂ heterobilayers. We observed a large enhancement of exciton g factors over g₀ (=4.5), with maxima approaching 100. The magnetic interactions peak at a filling factor of 1 electron per moiré site (ν=1) for R-stacked samples, but at ν=1.5 & 2.3 for H-stacking. At these filling factors, the temperature dependence of the g factors follows a Curie-Weiss law, yielding Weiss constants ~ 2 K and suggesting ferromagnetic interactions. Our results imply a phase diagram that differs from that of WSe₂/WS₂, expanding the range of correlated electron physics in moiré superlattices.