Angle-resolved photoemission spectroscopy study on graphene using circularly polarized light

We have investigated graphene using circularly polarized light via angle-resolved photoemission spectroscopy. We observe that photoelectron intensity rotates around a constant energy contour towards the opposite direction upon changing the chirality of light. Interestingly, the circular dichroism is found to be asymmetric with respect to the Dirac energy, which is not explained by the Berry phase effect (Liu et al 2011 Phys. Rev. Lett. 107 166803). We also report that the energy spectra taken using the light with different chiralities show a finite separation from each other. We discuss possible origins of the unusual circular dichroism observed in graphene.