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

TL;DR

This paper theoretically predicts the generation of Floquet-Weyl semimetals in Zn$_3$As$_2$ via resonant circularly polarized laser irradiation, revealing two distinct phases with unique band-touching and surface state properties.

Contribution

It introduces a novel mechanism for creating Floquet-Weyl semimetals through resonant optical excitation, detailing two different phases with distinct topological and electronic characteristics.

Findings

Two types of Floquet-Weyl semimetal phases identified

One phase exhibits quadratic band-touching, the other linear

Both phases host nontrivial surface states with different dispersions

Abstract

Floquet-Weyl semimetals (FWSMs) generated by irradiation of a continuous-wave laser with left-hand circular polarization (rotating in counterclockwise sense with time) on the group II-V narrow gap semiconductor Zn$_3$As$_2$ are theoretically investigated, where the frequency of the laser is set nearly {\it 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 $J_z=\pm3/2$ and a conduction band labeled as $J_z=\pm 1/2$, where $J_z$ represents the $z$-component of total angular momentum quantum number of $\Gamma$-point and a double sign corresponds. Here, one FWSM state composed of the up-spin Floquet sidebands relevant to $J_z=3/2$ 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 $J_z=-3/2$ 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, alteration of topological order, laser-induced magnetic properties, and so on.