Graphene superlattices formed by periodic strain are considered theoretically. It is shown that an electron energy spectrum consists of minibands obtained by folding of the cone at the boundaries of the superlattice Brillouin zone with very narrow anticrossing regions. Light absorption under direct interminiband transitions is shown to be frequency dependent and dichroic. Giant dichroism of absorption is demonstrated for doped graphene superlattices. Asymmetrical graphene superlattices act as quantum ratchets allowing for the generation of photocurrents at absorption of normally incident light. The helicity-dependent photocurrent spectrum is calculated for doped superlattices with various asymmetries.

• Received 3 November 2011

DOI:https://doi.org/10.1103/PhysRevB.84.235440