What is it about?
In this Letter, we utilize two accidental BICs to demonstrate dual-frequency intrinsic chirality without breaking σz symmetry. By carefully tuning structural parameters, we can manipulate the circularly polarized states (C points) located at the Γ-point in k-space, leading to the achievement of intrinsic chiral quasi-BICs. The dual-frequency intrinsic chirality can be dynamically controlled through changing the Fermi level of the graphene sustrate. Our studies provide an alternative approach for detecting and manipulating circularly polarized waves in the THz band and hold promising prospects for an array of applications including spin detectors, radar stealth, wave plates, and other chiroptical devices.
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Why is it important?
Terahertz (THz) bound states in the continuum (BICs) present a significant opportunity to achieve ultra-high quality (Q) factors in chiroptical responses, which are essential for high-resolution spin-selective devices. However, most high-Q chiroptical resonances rely on symmetryprotected BICs, attained either via electromagnetic oblique incidence or structural anisotropy to obtain extrinsic chirality (false chirality). Additionally, slight variations in the incident angle can significantly reduce the resonance Q-factor in spectral responses, and meticulous control of the degree of structural symmetry breaking is required to ensure both high-Q performance and strong CD signals, as fabrication imperfections can introduce additional scattering losses. Unlike SPBICs, ACBICs (accidental BICs) are tunable BICs that can be found in highly symmetrical systems. By carefully tuning parameters, one can manipulate the circularly polarized states (C points) located at the C-point in k-space. Consequently, ACBICs offer an effective method to realize ultra-high Q-factor intrinsic chirality without breaking C2 or σz symmetry or requiring EM oblique incidence.
Perspectives
Bound states in the continuum (BICs), identified as radiation singularities (V point) within continuous spectra that exhibit zero leakage, can achieve an infinite Q-factor and significantly enhance light–matter interactions. Our findings provide an effective method for achieving ultra-high Q-factor intrinsic chirality, which may have significant inspirations for the optical merging of BICs and high-harmonic generation.
rui zhang
Shanghai Jiao Tong University
Read the Original
This page is a summary of: Tunable terahertz intrinsic chiroptical absorption empowered by accidental bound states in the continuum, Applied Physics Letters, November 2024, American Institute of Physics,
DOI: 10.1063/5.0237546.
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