  We investigated ultrafast carrier dynamics in graphene with near-infrared
transient absorption measurement after intense half-cycle terahertz pulse
excitation. The terahertz electric field efficiently drives the carriers,
inducing large transparency in the near-infrared region. Theoretical
calculations using the Boltzmann transport equation quantitatively reproduce
the experimental findings. This good agreement suggests that the intense
terahertz field should promote remarkable impact ioniza- tion process, which
leads to suppression of optical phonon emission and results in efficient
carrier transport in graphene.
