Floquet-Weyl states at one-photon resonances in three-dimensional topological insulators

Quantum materials exhibit exotic phases and electronic responses under irradiation by circularly polarized light, which breaks time-reversal symmetry and generates Floquet replica bands. Recently, Floquet topological states arising from direct resonances have attracted much attention, e.g., the emergence of Floquet-Weyl points at a one-photon resonance, rather than topological features within the modulated original bands via high-frequency expansion. In this study, we investigate the effects of a one-photon resonance in a representative three-dimensional topological insulator, Bi$_2$Se$_3$, applying Floquet theory under circularly polarized light. We find that four pairs of Floquet-Weyl points emerge in the intermediate-frequency regime, mediated by hybridization between the original and one-photon-resonant Floquet bands, preserving the threefold rotational symmetry of the crystalline structure. Our numerical calculations demonstrate that tuning the chemical potential via hole doping yields a large anomalous Hall conductivity, directly associated with these Floquet-Weyl points. This work provides a highly accessible route toward the experimental realization of one-photon-resonant Floquet-Weyl semimetals.