Tip-induced nanoscale control of an electromagnetically induced transparency analog in a single terahertz metamolecule

In metamaterial analogs of electromagnetically induced transparency (EIT), near-field coupling between a radiative bright resonator and a subradiant dark resonator produces a narrow transparency window with steep dispersion. However, the direct observation and manipulation of this coupling in a single terahertz (THz) metamolecule is fundamentally challenged by the diffraction limit. Scattering-type scanning near-field optical microscope (s-SNOM) exploits strong field confinement at its tip to enable both super-resolution imaging and nanoscale modulation. Here, we utilize the s-SNOM tip as a nano-actuator to control the EIT-like response within a single metamolecule. By acquiring spatially resolved nano-spectra, we uncover a strong asymmetric response in the near-field across the dark mode resonator. We develop a coupled tri-oscillator model (CTOM) that decouples and quantifies two contributions: the inhomogeneous intrinsic bright–dark coupling and the tip-induced local field, which continuously modulate the transparency window up to full on–off switching. Our results establish the s-SNOM tip as both a quantitative nano-probe and a tuning element, opening new pathways for designing reconfigurable nanophotonic and biosensing devices.