Exploring interacting Floquet states in black phosphorus: Anisotropy and bandgap laser tuning

Abstract

Non-adiabatic interacting Floquet (or dressed) states arising from the intrinsic coupling between electrons and holes with off-resonant electromagnetic radiation have been investigated for recently synthesized ultrathin gapped and anisotropic black phosphorus. Our analytical calculations were carried out for the low-energy electronic subbands near the Γ point. Optical dressed states for both linear and circular polarizations of the incoming radiation have been obtained and analyzed. We focus our attention on linearly polarized light with arbitrary polarization direction since this case has not been considered for dressing fields imposed on initially anisotropic structures. We have examined and compared various cases for one- and few-layer phosphorus, including massless Dirac fermions with laser tunable in-plane anisotropy. The electronic properties, such as bandgaps, Fermi velocities, and effective masses, are renormalized in a very different way compared to those for the previously studied gapped Dirac structures. More importantly, material anisotropy and angular dependence of energy dispersions could be tuned by incident polarized light in the individual direction. The interaction of electrons with photons brings out a product term for two wave-vector components in energy dispersions, which leads to non-vanishing off-diagonal elements in inverse effective-mass and momentum-relaxation-time tensors and is expected to have a significant effect on the conductivities of electrons and holes. Such unique features in the band structure can be applied to new designs and fabrications of optical transistors and logic devices used in optical computers and communications.