Dual-band circular dichroism in chiral metamaterial absorber based on vanadium dioxide

Chiral metamaterial absorbers are instrumental in a wide array of applications, encompassing multifaceted optoelectronic devices, information-encrypting metamaterials, and thermal-controlled imaging and detection systems. In this study, we showcase a Ꞩ-shaped chiral metamaterial integrated with a vanadium dioxide substrate, which enables dynamic tuning of THz dual-band circular dichroism. This absorber boasts spin-selective absorption, stemming from the selective excitation of the plasmon polaron mode on its horizontal microrod. Notably, right-handed circularly polarized light experiences near-perfect absorption at resonance, whereas left-handed circular polarization is absorbed to a much lesser degree, yielding pronounced circular dichroism. This exceptional chiral selectivity facilitates dual-band circular dichroism effects, with peak values reaching 0.814 and 0.784. Furthermore, by manipulating the conductivity of vanadium dioxide, we can dynamically adjust both the circular dichroism and absorption peaks of the chiral metamaterial. The maximum modulation depth of the circular dichroism response can attain values as high as 0.807 and 0.776. Our work presents a novel design strategy for the active control and modulation of circularly polarized light, thereby expanding the horizons of metamaterial absorber applications within the THz spectrum.