  We theoretically investigate detuning-dependent properties of high-order
harmonic generation (HHG) in monolayer transition metal dichalcogenides
(TMDCs). In contrast to HHG in conventional materials, TMDCs show both parallel
and perpendicular emissions with respect to the incident electric field. We
find that such an anomalous emission can be artificially controlled by the
frequency detuning of the incident electric fields, i.e., the parallel and
perpendicular HHG can be strongly enhanced by multiphoton resonances. This
peculiar phenomenon would provide a way for controlling HHG in TMDCs and
stimulate the realization of novel optical devices.
