Ultrafast Photocurrents in the Weyl Semimetal TaAs

We investigate polarization-dependent, ultrafast photocurrents in the Weyl semimetal TaAs using terahertz (THz) emission spectroscopy. Our results reveal that highly directional, transient photocurrents are generated along the non-centrosymmetric c-axis regardless of incident light polarization, while helicity-dependent photocurrents are excited within the ab-plane. This is consistent with both the bulk photovoltaic effect and the circular photogalvanic effect observed in direct photocurrent experiments, and provides additional insight into their microscopic origin by way of the dynamical information gained from the emitted THz waveform.