  The concept of the chiral gauge field (CGF), originally developed in
theoretical particle physics, has now emerged in condensed matter systems in
materials known as Weyl semimetals. In general, Weyl semimetals emerge from
Dirac semimetals when time-reversal or spatial-inversion symmetries are broken.
Recently, it has gained a growing interest to manipulate such topological
states of matter by implementing the CGF by shining light to materials. Here we
have demonstrated the emergence of CGF in a massive 3D Dirac electron system in
the paramagnetic phase of Co3Sn2S2, which exhibits a ferromagnetic Weyl
semimetal phase at low temperatures. We first show theoretically that the
illumination of circularly polarized light implements the CGF in the
paramagnetic state of Co3Sn2S2 and gives rise to a topological Weyl state,
which can be realized only in the nonequilibrium state. Then we demonstrated
that the presence of light-induced CGF through the observation of light-induced
anomalous Hall effect, the behavior of which quantitatively agrees with the
calculation from the Floquet theory. The light-induced AHE manifests the Berry
curvature which becomes nonzero as the bands split due to the light-induced
CGF. Our demonstration paves a new pathway for ultrafast manipulation of
topological phases in 3D Dirac semimetals and for further exploring new quantum
matter phases which can be only achieved by light.
