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Inspired by the chiral structure from mode interaction, a chiral terahertz metamaterial and its complementary structure with the coexistence of asymmetric transmission and circular dichroism response are designed. The asymmetric transmission happens in the presence of electric and magnetic modes perpendicular to each other, resulting from intrinsic chirality under normal incidence. Circular dichroism exists in the presence of electric and magnetic modes parallel to each other under oblique incidence because of extrinsic chirality. Both asymmetric transmission and circular dichroism are enhanced by complementary structures, benefitting from the coupling between adjacent units. The maximum of chiral parameter κ can achieve 450, which is one hundred times higher than previously reported. The chiral response can be tuned by the incident angle and is sensitive to the environmental refractive index. The results highlight the potential applications of these metamaterials in chiral sensing and polarization transformation devices. [ABSTRACT FROM AUTHOR]

Giant plasmonic mode splitting has been observed in THz metamaterials due to the mediation by the Lorentz phonon dielectric material. This splitting mode is confirmed by the surface current distribution, indicating that plasmonic modes behave like dipole resonances, while the phonon mode behaves like multipole resonance due to coupling. The splitting of the plasmonic modes demonstrates an anti-crossing behavior with the change in Lorentz central frequency, which suggests that there is energy redistribution between plasmon and phonon modes. Similar to the Stark effect, the splitting frequency difference increases with the increasing direct current dielectric function. We also propose an interaction Hamiltonian to understand the physical mechanism of the plasmonic splitting. Furthermore, the splitting is convincible for small Lorentz dielectrics such as sugar and amino acid in the THz region, which could be used for biomolecular sensing applications. [ABSTRACT FROM AUTHOR]

Chirality, as the core code of life forms, connects the ultimate secret of life and universe evolution. In article number 1900398, Changji Liu and co-workers propose an intrinsic chiral metamaterial and its complementary structures with coexistence of circular asymmetric transmission and circular dichroism in the THz region. The analysis reveals the chirality in metamaterials mainly comes from mode interaction and can be tuned by the incident angle. [Extracted from the article]

Two-dimensional chirality induced polarization conversion and asymmetric transmission have great potential for polarization applications. We propose graphene-based planar chiral metamaterial and its complementary structure with dual functionality of both circular polarization conversion and asymmetric transmission in terahertz (THz) region. The conversion efficiency of chiral structure can reach up to 37.33/λ, which is comparable with three-dimensional chiral structure made of metal due to the unique optoelectronic properties of graphene. The transmission asymmetry of complementary chiral metamaterial originating from the high order plasmonic resonance can be tuned from 0.049% to 3.504% by changing Fermi energy, and the asymmetry can also be enhanced via geometrical optimization. This work raises the prospect of switchable, compact, and on-chip THz polarized devices with graphene materials. [ABSTRACT FROM AUTHOR]