  Photoinduced topological phase transitions (TPTs) in black phosphorous (BP)
under compressive strain were investigated by combining Floquet theory and
first-principles calculations. Intriguing photo-dressed electronic states
including Floquet-Dirac semimetals and Floquet topological insulators have been
identified, which can be feasibly engineered by changing the direction,
intensity and frequency of incident laser. Remarkably, tunable TPT from type-I
to type-II Floquet-Dirac fermions can be realized by irradiating circularly
polarized laser (CPL), with an origin rooted in optical Stark effect.
Furthermore, the photoinduced Floquet-Dirac phases is shown to host topological
surface states that exhibit nonequilibrium electron transport in a direction
locked by the helicity of CPL. This work provides useful guidance for
experimental observation of Floquet TPTs, and extends optoelectrionic
applications of BP to nonequilibrium regime.
