Actively Tunable Terahertz Slow-Light via Plasmon-Induced Transparency in Graphene Metasurface

Abstract Plasmon-induced transparency (PIT) metasurfaces provide a compact and efficient route to slow-light operation and dispersion engineering in the terahertz (THz) regime. In this work, we propose and numerically investigate a THz graphene metasurface composed of a circular disk and a ribbon resonator, where a pronounced PIT response is enabled by near-field coupling between a radiative bright mode and a weakly radiative dark mode. By combining three-dimensional finite-difference time-domain (FDTD) simulations with coupled-mode theory (CMT), the physical origin of the PIT window and its spectral evolution are systematically elucidated, showing excellent agreement in both resonance positions and line-shape characteristics. Through synchronous modulation of the graphene Fermi level from 0.5 eV to 1.1 eV, the PIT window exhibits continuous frequency reconfiguration and enhanced spectral selectivity, with the quality factor (Q) increasing from 9.8441 to 11.8714. Further geometric optimization reveals that tailoring the disk radius and ribbon width can significantly sharpen the PIT response, yielding a maximum Q of 15.6865. Moreover, the PIT feature remains nearly unchanged under moderate inplane misalignment, indicating good fabrication tolerance. Benefiting from the steep phase dispersion near the PIT window, the proposed design exhibits an enhanced slow-light effect with a maximum group index of 1.882 × 10 4 and a group delay of 188.28 ps. These results provide a practical strategy for compact and electrically tunable THz slow-light and phasemanipulation devices.