  We observe that the illumination of unbiased graphene in the quantum Hall
regime with polarized terahertz laser radiation results in a direct edge
current. This photocurrent is caused by an imbalance of persistent edge
currents, which are driven out of thermal equilibrium by indirect transitions
within the chiral edge channel. The direction of the edge photocurrent is
determined by the polarity of the external magnetic field, while its magnitude
depends on the radiation polarization. The microscopic theory developed in this
paper describes well the experimental data.
