  Semiconductor moir\'e heterostructures exhibit rich correlation-induced
many-body phenomena with signatures of emergent magnetism, Mott insulating
states or generalized Wigner crystals observed in optical spectroscopy by
probing intralayer excitons. However, as the staggered band alignment in the
underlying WSe$_2$/WS$_2$ heterobilayer system separates photoexcited electrons
and holes to form lowest-energy interlayer excitons, direct access to
interactions between correlated charge states and ground state moir\'e excitons
remained elusive. Here, we use MoSe$_2$/WS$_2$ heterostacks with type-I band
alignment to probe Coulomb interactions of elementary charges with the ground
and excited states of moir\'e excitons. In addition to positive and negative
moir\'e trions reminiscent of their canonical counterparts in monolayer
MoSe$_2$, we reveal novel many-body states formed between moir\'e excitons and
charges at fractional filling factors of the periodic moir\'e lattice. For both
electrons and holes, these states exhibit doping-dependent Land\'e factors as a
hallmark of correlation-induced magnetism, identifying the MoSe$_2$/WS$_2$
heterobilayer as a unique system for studies of correlated phenomena in
ambipolar doping regimes.
