Light-induced chiral gauge field in a massive 3D Dirac electron system

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.