Ultrafast Processes in Weyl semimetals

We theoretically study the electron dynamics of topological Weyl semimetals in both linear and circularly ultrafast optical pulse. We use the effective model in the reciprocal space near the Weyl points. We present the results for TaAs. For linear optical pulse, the electron dynamics for each set of Weyl point is different and strongly depends on the polarization direction of the pulse. In circularly polarized ultrafast pulse, we predict that the electron dynamics is coherent and highly irreversible. For a pulse propagating in the z-direction, the conduction band (CB) population in reciprocal space not only depends on the profile of the dipole matrix elements but also depends on the band gap. For small band gaps, the system behaves similarly to graphene with a localized dipole matrix near (k_x,k_y)=(0,0) point which causes a large CB population along the separatrix which is defined as a mirror-symmetric of the electron trajectory in the reciprocal space. However, for large k_z, the system is similar to the gapped graphene with delocalized interband dipole matrix, and therefore the CB population is not confined within a narrow region. We also show that both linear and circularly polarized pulse causes an electrical current and net charge transfer through the system during the pulse.