Abstract

Terahertz metasurfaces capable of dynamic modulation face a fundamental trade-off: high-quality-factor resonances require structural symmetry, but active tuning typically relies on symmetry-breaking that inevitably introduces radiative losses. This study presents a theoretical analysis of tunable terahertz metasurfaces utilizing vanadium dioxide (VO2) as an active component that circumvents this trade-off through current-loop-mediated symmetry control. Based on the current-loop-mediated coupled-mode theory, we establish a quantitative relationship between VO2’s conductivity and resonant mode characteristics through the symmetry-breaking parameter α(σ)∝∮(r×K(σ))⋅dl. The proposed theoretical framework describes the conversion mechanism between non-radiative bound states in the continuum (BIC) and radiative quasi-BIC (qBIC), where VO2’s metal–insulator phase transition modulates surface current distributions and activates radiation channels. Through systematic analysis of multiple metasurface designs, we demonstrate that conductivity-dependent current-loop formation governs the switching between high-Q dark modes and radiative states, achieving modulation depths up to 243%—providing a robust approach for dynamic terahertz wave manipulation with explicit physical linkage between materials parameters and modal properties.

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