Terahertz ratchet effects in graphene with a lateral superlattice

Abstract

This paper reports on the experimental realization of ratchet effects in graphene, excited by alternating electric fields of terahertz frequency range. Such ratchet effects were previously seen in semiconductors. Two types of graphene lateral superlattices are studied: epitaxially grown and exfoliated graphene with an asymmetric lateral periodic potential. Laser radiation shining on the modulated devices results in the excitation of a direct electric current being sensitive to the radiation's polarization state. This ratchet current consists of a few linearly independent contributions including the Seebeck thermoratchet effect as well as ``linear'' and ``circular'' ratchets. The results are analyzed with a theoretical model. Further development of the theory is required for a quantitative analysis.