Magnetically induced high Q quasi-bound state in the continuum mode via fundamental lattice mode coupling in complementary terahertz metasurface

Metasurfaces have emerged as powerful platforms for controlling electromagnetic waves through field confinement and resonance engineering. This work investigates the interplay between magnetic field-driven quasi-Bound State in the Continuum (quasi-BIC) resonance and lattice mode coupling in a complementary metasurface comprising coupled bar resonators. By introducing opposite tilts in the bar resonators, we observe the emergence of sharp resonance resulting from anti-symmetric current distributions, forming a quasi-BIC mode with strong field confinement. It is observed that the strategic change in periodicity significantly enhances the quality factor of the resonance, reaching maximum when the quasi-BIC mode couples to the fundamental lattice mode. We performed terahertz time domain spectroscopy of the fabricated samples and observed that the results are consistent with simulations, further confirming a strong interaction between the modes. These findings opens up an avenue for designing high-Q low loss metasurfaces with potential applications in sensing, filtering, and terahertz photonic devices.