Light-induced valleytronics in pristine graphene

Electrons in two-dimensional hexagonal materials have valley degree of freedom, which can be used to encode and process quantum information. The valley-selective excitations, governed by the circularly polarised light resonant with material's band-gap, continues foundation valleytronics. It is often assumed that achieving selective excitation pristine graphene all-optical means not possible due inversion symmetry system. Here we demonstrate both high-harmonic generation achieved using combination two counter-rotating polarized fields, fundamental its second harmonic. Controlling relative phase between colours allows us select valleys where electron-hole pairs higher-order harmonics are generated. We also describe an method for measuring polarization a weak probe pulse. This work offers robust recipe write read electron excitations zero bandgap Berry curvature.