Ultrafast nonlinear electron dynamics in gapped graphene*

We theoretically study the ultrafast electron dynamics in gapped graphene. Graphene consists of two equivalent sublattices and has both inversion and time-reversal symmetries. Breaking the inversion symmetry in graphene opens the bandgap and makes sublattices inequivalent. Gapped graphene is used as a model for a broad class of two-dimensional materials, including transition metal dichalcogenides. The ultrafast electron dynamics in gapped graphene is induced by a linearly polarized ultrafast optical pulse applied perpendicular to graphene monolayer. Our results show that the residual, i.e., after the pulse, conduction band (CB) population, which characterizes the irreversibility of the electron dynamics, is large and shows interference fringes in the reciprocal space. The finite bandgap in graphene makes the electron dynamics partially reversible, which manifests itself in smearing of the interference fringes in the CB population distribution.