Photoinduced topological phase transition and optical conductivity of black phosphorene

Abstract

We theoretically study the photoinduced topological phase transition of black phosphorene induced by laser light with moderate intensity, which can satisfy the experimentally realistic requirement to preserve the quality of the sample. By deriving the effective Floquet Hamiltonian in terms of pseudospin $S=1/2$ degrees of freedom, we calculate the Chern number and the optical conductivity of the system with varying laser frequency $\mathrm{\ensuremath{\Omega}}$. As one can expect from the photon-assisted transport, the longitudinal optical conductivity has a threshold frequency at $\mathrm{\ensuremath{\Omega}}=\mathrm{\ensuremath{\Delta}}/\ensuremath{\hbar}$, with $\mathrm{\ensuremath{\Delta}}$ being the band gap of black phosphorene. Unlike the longitudinal optical conductivity, the optical Hall conductivity sharply increases when $\ensuremath{\hbar}\mathrm{\ensuremath{\Omega}}$ goes beyond one-half of the band gap $\mathrm{\ensuremath{\Delta}}/2$. We also show that the Chern number changes from trivial to nontrivial upon increasing frequency $\mathrm{\ensuremath{\Omega}}$ beyond $\ensuremath{\hbar}\mathrm{\ensuremath{\Omega}}=\mathrm{\ensuremath{\Delta}}/2$.