  In recent years, coherent electrons driven by light fields have attracted
significant interest in exploring novel material phases and functionalities.
However, observing coherent light-field-driven electron dynamics in solids is
challenging because the electrons are scattered within several ten femtoseconds
in ordinary materials, and the coherence between light and electrons is
disturbed. However, when we use Weyl semimetals, the electron scattering
becomes relatively long (several hundred femtoseconds - several picoseconds),
owing to the suppression of the back-scattering process. This study presents
the light-field-driven dynamics by the THz pulse to Weyl semimetal Co3Sn2S2,
where the intense THz pulse of a monocycle electric field nonlinearly generates
direct current (DC) via coherent acceleration without scattering and
non-adiabatic excitation (Landau-Zener Transition). In other words, the
non-Ohmic current appears in the Weyl semimetal with a combination of the long
relaxation time and an intense THz pulse. This nonlinear DC generation also
demonstrates a Keldysh crossover from a photon picture to a light-field picture
by increasing the electric field strength.
