Tunable chiral metasurface for spin-selective absorption and reflective focusing effect for terahertz wave based on vanadium dioxide (VO2)

• This paper proposes a tunable chiral metasurface (CMS) composed of double-asymmetric-split-rings (DASRs) structure integrated with VO 2 pads adhered on a dielectric substrate backed with a metal ground plane. • The designed tunable CMS with VO 2 at insulating state ( σ VO₂ = 2×10 2 S/m) can achieve absorbance of 99.5% for RHCP wave and 93.0% for LHCP wave at 2.39 THz and 3.07 THz, respectively. • Increasing the conductivity of VO 2 from 2×10 2 S/m to 2×10 5 S/m allows continuous adjustment of the CD value at 2.39 THz and 3.07 THz within ranges of 0 to 0.75 and 0 to -0.86. • The designed MS can achieve a reflective focusing effect with tunable efficiency for the incident LHCP wave and high absorption for the RHCP wave at 3.07 THz. In this paper, a tunable reflective chiral metasurface (CMS) based on vanadium dioxide (VO₂) is proposed for spin-selective absorption and reflective wavefront manipulation in the terahertz (THz) regime. The CMS unit cell comprises a double-asymmetric-split-rings (DASRs) structure integrated with VO₂ pads, adhered to a dielectric substrate and backed by a metallic ground plane. Numerical simulations reveal that, in the insulating state of VO₂ (σ VO₂ = 2×10² S/m), the CMS achieves exceptional spin-selective absorption efficiency with absorbance of 99.5% for right-handed circularly polarized (RHCP) waves at 2.39 THz and 93.0% for left-handed circularly polarized (LHCP) waves at 3.07 THz. This performance yields notable circular dichroism (CD) values of ±0.74 and ±0.86 at 2.39 THz and 3.07 THz, respectively. Leveraging the Pancharatnam–Berry (PB) phase principle, the design enables full 360 ° reflection phase modulation through DASR orientation angle adjustment. Theoretical analyses confirm simultaneous realization of high spin-selective absorption and independent wavefront control for orthogonal circular polarization at identical frequencies. As a proof-of-concept, a CMS prototype is numerically validated to exhibit high LHCP absorption and RHCP reflected focusing at 3.07 THz. This multifunctional CMS platform offers promising potential for advancing wireless communication systems, polarization-encoded signal processing, and chiral spectroscopy applications.