Optical Control of Chiral Charge Pumping in a Topologcial Weyl Semimetal

Solids with topologically robust electronic states exhibit unusual electronic and optical transport properties not seen in other materials. A peculiar example is chiral charge pumping (also called chiral anomaly) in recently discovered topological Weyl semimetals, where simultaneous application of parallel static electric and magnetic fields causes an imbalance in the number of topological chiral carriers. Here, using time-resolved terahertz measurements on the Weyl semimetal tantalum arsenide (TaAs) in a magnetic field, we uncover the optical control of chiral anomaly by dynamically pumping the chiral charges and monitor their relaxation. Rigorous theory based on Boltzmann transport shows that the observed optically-induced control of chiral anomaly is governed by the optical nonlinearity in the chiral charge pumping process. Our measurements reveal that the chiral pumping relaxation is much longer than 1 ns. The optically-controlled long-lived chiral carriers observed here in a Weyl semimetal exhibit similar behavior to the valley-polarized carriers in 2D semiconductors, but with the extra feature of topological protection, suggesting possible valleytronic applications of Weyl semimetals.