Dynamical Floquet spectrum of Kekulé-distorted graphene under normal incidence of electromagnetic radiation

Electromagnetic dressing by a high-frequency field drastically modifies the electronic transport properties on Dirac systems. Here its effects on the energy spectrum of graphene with two possible phases of Kekul\'e distortion (namely, Kek-Y and Kek-O textures) are studied. Using Floquet theory it is shown how circularly polarized light modifies the gapless spectrum of the Kek-Y texture, producing dynamical band gaps at the Dirac point that depends on the amplitude and the frequency of the electric field, and breaks the valley degeneracy of the gapped spectrum of the Kek-O texture. To further explore the electronic properties under circularly polarized radiation, the dc conductivity is studied by using the Boltzmann approach and considering both inter-valley and intra-valley contributions. When linearly polarized light is considered, the band structure of both textures is always modified in a perpendicular direction to the electric field. While the band structure for the Kek-Y texture remains gapless, the gap for the Kek-O texture is reduced considerably. For this linear polarization it is also shown that non-dispersive bands can appear by a precise tuning of the light field parameters thus inducing dynamical localization. The present results suggest that optical measurements will allow to distinguish between different Kekul\'e bond textures.
Comment: 14 pages, 5 figures