Ultrashort laser-driven dynamics of massless Dirac electrons generating valley polarization in graphene

Abstract

We identify and describe how intense short light pulses couple to massless Dirac fermions in two-dimensional systems. The ensuing excitation dynamics exhibits unusual scaling with the wavelength of the light due the linear dispersion of the band structure and the fact that light coupling is efficient only close to the Dirac points. We exploit these features to achieve valley polarization of more than 70% with simple pulse shapes. Thereby, we demonstrate that substantial valley polarization at moderate excitation can be achieved with a suitable linearly polarized pulse in gapless systems. Quantitative results are given for pristine graphene.