Active terahertz spin Hall effect in vanadium dioxide metasurfaces

Insulator-to-metal transition induces large material property variations in vanadium dioxide (VO₂) over a broad frequency band. VO₂, therefore, has been introduced into metallic resonating structures to realize reconfigurable metadevices from microwave to optical wavelengths. Beyond enabling metal/VO₂ hybrid meta-atoms, in the THz regime metallic-phase VO₂ microstructures can support strong electromagnetic resonances, offering great potential in active manipulation of THz radiation. In this paper, we show that VO₂ dipole antennas can be used to realize geometric phase coded metasurfaces for wave-front shaping and polarization rotation of THz waves. Moreover, we demonstrate that the corresponding efficiency of the THz spin Hall effect is closely related to VO₂'s THz electrical conductivity. In light of the dispersionless nature of the geometric phase, our study indicates that metasurfaces constructed by VO₂ subwavelength resonators are good candidates for active control of broadband THz radiation.