Figure 1 | Chiral metasurface enabled by zero-topological-charge (ZTC) merging BICs with wide k-domain chirality. (IMAGE)
Caption
Figure 1 | Chiral metasurface enabled by zero-topological-charge (ZTC) merging BICs with wide k-domain chirality. a, Schematic of a planar chiral metasurface composed of square island meta-atoms perforated by a pair of holes (P = 836 nm, L = 746 nm, R = 70 nm, t = 220 nm). The inset displays measured Q-factors and circular dichroism (CD) versus incidence angle. b,c, Comparison between a conventional chiral symmetry-protected (SP) BICs (b) and the proposed ZTC BICs design (c). In contrast to SP-BICs, which exhibit rapid Q-factor decay away from the Γ point, the ZTC merging BICs concept supports high-Q chiral resonances across broader momentum and parameter ranges. d, Schematic of the 2×2 unit cell of the initial degenerate parabolic bands at the Γ point prior to symmetry breaking. e, Band structure illustrating that the reduction from C4 to C2 symmetry lifts the degeneracy, generating a pair of Dirac points along kx. f, Dissociation of the ZTC merging BICs into multiple accidental BICs distributed around the Γ point, achieved by tuning the in-plane parameter dy. g, Mechanism for establishing the chiral domain. Breaking out-of-plane symmetry (substrate ns > 1) splits the integer-charge accidental BICs into pairs of half-integer C-points. A subsequent lateral perturbation dx triggers topological charge inversion via interaction with the Dirac points, while simultaneously rotating the singularity distribution in k-space and segregating left-handed C-points, resulting in a robust, broad intrinsic chiral domain.
Credit
Jinhui Shi et al.
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CC BY