Multipole resonances-mediated dual-band tunable circular dichroism via vanadium dioxide chiral metamaterials

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Chiral response based on phase transition metamaterial of vanadium dioxide (VO2) is a promising candidate for chirality-related applications such as biochemical sensing, spectral detection, and advanced imaging. However, chiroptical peaks of VO2 chiral metamaterials are usually vanished after VO2 undergoes the phase transition from metallic state to dielectric state, which limits the dynamic control of their chiral properties. Herein, we propose a complementary z-shaped VO2 chiral metamaterial to achieve dual-band circular dichroism (CD) responses, and the two resonant CD peaks can be maintained in both metallic and dielectric states of VO2. The mechanisms of the novel robust CD responses are associated with the excitations of hybrid multipole resonances according to the far-field multipole decomposition and the near-field distribution of the device, and their peak values as well as their resonance locations can be dynamically tuned in the mid-infrared region by changing the volume fraction. In addition, the variations of the length and the width of the proposed device slightly alter the CD responses particular the resonance location, but the CD responses are almost immune to the variation of its height. Highlights The concept of multipole resonances-mediated tunable CD is proposed via the VO2-based chiral metamaterials. Robust dual-band CD responses associated with the excitation of hybrid multipole resonances are demonstrated. The peak value, frequency and bandwidth of CD response can be dynamically tuned by changing volume fraction. Good CD performances can be maintained even if the geometrical parameters are significantly altered.