Ultrafast active 3D Dirac terahertz metadevice

Cadmium arsenide (Cd3As2), a three-dimensional Dirac semimetal and analog of graphene, exhibits ultrafast optical modulation of its metallic and dielectric properties. Benefiting from the linear band dispersion and ultrahigh electronic mobility, Cd3As2 supports ultrafast carrier dynamics and tunable terahertz (THz) electromagnetic responses. In this work, ultrathin (130 nm) Cd3As2 films are patterned with a periodic hole array to engineer geometric resonances and realize an optically switchable ultrafast THz metadevice. Optical pump–THz probe spectroscopy reveals that small pump fluence induces significant changes in conductivity, enabling the emergence and active tuning of resonance features on picosecond timescales. The device demonstrates ultrafast carrier relaxation time of 25 ps, low power operation, and all-optical THz modulation with a switching speed of up to 40 GHz. These results highlight the advantages of Cd3As2 for next-generation THz optoelectronic devices and open pathways for scalable, high-speed metadevices based on topological 3D Dirac materials.