Multiband and continuously tunable circular dichroism in twisted terahertz chiral metasurface absorbers

Circular dichroism (CD) in chiral metasurface absorbers arises from the different absorption responses to left-handed and right-handed circularly polarized waves. However, many existing designs are mainly optimized for a single spectral band and exhibit limited tunability. Here, we introduce a twist-angle-controlled terahertz chiral metasurface absorber, in which geometric rotation enables multiband spin-selective absorption with twist-dependent resonance shifts and pronounced CD responses. Simulations show that the proposed metasurface supports multiband spin-selective absorption, with the maximum CD reaching 0.96 at 1.162 THz. Moreover, we confirm such strong CD value stemming from the electric dipole response by utilizing the method of charge-current multipole expansion. Our designs offer a twist-angle-based strategy for developing multiband chiral metasurface absorbers beyond conventional fixed-geometry designs, which may benefit the development of polarization-selective terahertz devices.