Dynamically reconfigurable dual-band circular dichroism in a terahertz hybrid dielectric-graphene metasurface

Circular dichroism (CD) is a crucial physical quantity characterizing the differential response of chiral systems to circularly polarized light, holding broad application value in polarization control, chiral recognition, and high-sensitivity sensing. However, existing metasurface devices predominantly operate in single-band or static regimes, failing to meet the demands for multiband coordinated control and dynamic tunability. To overcome these limitations, we numerically investigate a dynamic metasurface based on a polymethylpentene (TPX)–LiTaO3–graphene hybrid platform. By introducing multiple geometric symmetry breakings, two strong and spectrally distinguishable CD resonances are achieved within the target spectral range, thereby enabling a dual-band CD response. The corresponding maximum CD values reach 0.89 and 0.99, with Q factors of 36,283 and 9,202, respectively. The CD enhancement mechanism is elucidated through k-space analysis, multipole decomposition, and electric field distributions. Furthermore, dynamic modulation of the dual-band CD is achieved via Fermi level tuning of graphene, which modifies its surface conductivity. The two resonances exhibit distinct absolute CD modulation amplitudes of 0.86 and 0.54, respectively. The sensing performance of the proposed chiral metasurface is evaluated, and the results show that the dual-band CD resonances exhibit different sensitivities to changes in the surrounding refractive index, providing two distinguishable sensing channels. This work presents a novel strategy for dynamically controlling multi-band chiral light fields, with potential applications in electrically tunable terahertz chiral devices and dual-resonance refractive-index sensing.