  In this paper we develop the excitonic theory of Kerr rotation angle in a
two-dimensional (2D) transition metal dichalcogenide at zero magnetic field.
The finite Kerr angle is induced by the interplay between spin-orbit splitting
and proximity exchange coupling due to the presence of a ferromagnet. We
compare the excitonic effect with the single particle theory approach. We show
that the excitonic properties of the 2D material lead to a dramatic change in
the frequency dependence of the optical response function. We also find that
the excitonic corrections enhance the optical response by a factor of two in
the case of MoS2 in proximity to a Cobalt thin film.
