Response of electronic systems in intense lights (AC electric fields) to DC source-drain fields is formulated with the Floquet method. We have then applied the formalism to graphene, for which we show that a non-linear effect of a circularly polarized light can open a gap in the Dirac cone, which leads to a photo-induced dc Hall current. This is numerically confirmed for a graphene ribbon attached to electrodes with the Keldysh Green's function.
@article{arxiv.0807.4767,
title = {Photovoltaic Hall effect in graphene},
author = {Takashi Oka and Hideo Aoki},
journal= {arXiv preprint arXiv:0807.4767},
year = {2009}
}