The “artificial magnetic” resonance in the plasmonic metamolecule extend the potential application of magnetic resonance from terahertz to optical frequency bypassing the problem of the magnetic response saturation by replacing the conduction current with the ring displacement current. So far the magnetic Fano resonance-induced nonlinearity enhancement in the plasmonic metamolecule rings have not been reported. Here we use the magnetic Fano resonance to enhance the second-harmonic generation (SHG) in plasmonic metamolecule rings. In the spectra of the plasmonic matamolecule, an obvious Fano dip appears in the scattering cross cection, while the dip does not appear in the absorption cross section. It indicates at the Fano dip the radiative losses are suppressed while the optical absorption efficiency is at a high level. The largely enhanced SHG signal is observed as the excitation wavelength is adjusted at the magnetic Fano dip of the plasmonic metamolecule rings with stable and tunable magnetic responses. We also compare the magnetic Fano dip with the electric case to show its advantages in enhancing the fundamental and the second harmonic responses. Our research provides new thought for enhancing the optical nonlinear processes by the magnetic modes.
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