  The discovery of monolayer graphene has initiated two fertile fields in
modern condensed matter physics, Dirac semimetals and atomically-thin layered
materials. When these trends meet again in transition metal compounds, which
possess spin and orbital degrees of freedom and strong electron correlations,
more exotic phenomena are expected to emerge in the cross section of
topological states of matter and Mott physics. Here, we show by using ab initio
calculations that a monolayer form of transition metal trichalcogenides (TMTs),
which has a honeycomb network of transition metal cations, may exhibit multiple
Dirac cones with tunable gaps in the electronic structure. Furthermore, we
elucidate that electron correlations and carrier doping turn the multiple-Dirac
semimetal into a topological ferromagnet with high Chern number. Our findings
raise the honeycomb-monolayer TMTs to a new paradigm to explore correlated
Dirac electrons and topologically-nontrivial magnetism. In turn, the unique
wide-ranging properties of the materials will deliver new building blocks for
atomically thin heterostructures.
