Topological properties of graphene on a nanowire superlattice subjected to ultrafast circular pulses

We report on the direct manifestation of topological nature of graphene in the conduction band population distribution without a magnetic field. The crystalline structure of graphene coupled to a nanowire superlattice, and driven by a few-cycle circularly polarized optical field, reduces the symmetry of the states and allows for observing the Berry phase in the reciprocal space. Such an effect can be read-out with time- and angle-resolved photoelectron emission spectroscopy (Tr-ARPES).