Floquet-Weyl semimetals generated by an optically resonant interband-transition

Abstract

Floquet-Weyl semimetals (FWSMs) generated by irradiation of a continuous-wave laser with lefthand circular polarization (rotating in counterclockwise sense with time) on II3-V2-type narrow gap semiconductor Zn3As2 are theoretically investigated, where the frequency of the laser is set nearly resonant with a band gap of the crystal. It is found that the excitation of the crystal by such a laser induce two types of FWSM phases that differ absolutely in characters. To be specific, the associated two pairs of Weyl points are stably formed by band touching between Floquet sidebands ascribable to a valence band labeled as Jz = ±3/2 and a conduction band labeled as Jz = ±1/2, where Jz represents the z-components of total angular momentum quantum number of Γ-point and a double sign corresponds. Here, one FWSM state composed of the up-spin Floquet sidebands relevant to Jz = 3/2 and 1/2 shows almost quadratic band-touching in the vicinity of the associated pair of Weyl points, while the other FWSM state composed of the down-spin Floquet sidebands relevant to Jz = −3/2 and −1/2 shows linear band-touching. Further, it is revealed that both up-spin and down-spin sidebands host nontrivial two-dimensional surface states that are pinned to the respective pairs of the Weyl points. Both surface states also show different energy dispersions and physical properties. More detailed discussion is made in the text on the origin of the above findings, chirality of the FWSM phases, laser-induced magnetic properties, and so on.