  We have studied helicity dependent photocurrent (HDP) in Bi-based Dirac
semimetal thin films. HDP increases with film thickness before it saturates,
changes its sign when the majority carrier type is changed from electrons to
holes and takes a sharp peak when the Fermi level lies near the charge
neutrality point. These results suggest that irradiation of circularly
polarized light to Dirac semimetals induces an effective magnetic field that
aligns the carrier spin along the light spin angular momentum and generates a
spin current along the film normal. The effective magnetic field is estimated
to be orders of magnitude larger than that caused by the inverse Faraday effect
(IFE) in typical transition metals. We consider the small effective mass and
the large $g$-factor, characteristics of Dirac semimetals with strong spin
orbit coupling, are responsible for the giant IFE, opening pathways to develop
systems with strong light-spin coupling.
