Magnetic quadrupolar resonance in a symmetric three-layered plasmonic metasurface

Dark plasmon mode with even symmetry presents an effective way for manipulating light-matter interactions due to its attractive properties of small radiative loss and strongly intensified near-field, which opens up space for both fundamental explorations and optoelectronic device developments. In this paper, we demonstrate magnetic quadrupolar resonance in a symmetric plasmonic metasurface under oblique light incidence. In a three-layered metasurface made of a cross-shaped gold array on top of a magnesium fluoride film backed with a copper ground plane, a magnetic quadrupolar resonance is excited at 37.3 THz with a quality factor of 34, which is four times of the regular magnetic dipolar resonance excited in the same structure. By increasing the incident angle, asymmetry perturbation on the magnetic quadrupolar mode becomes more pronounced as evidenced from its decreased quality factor. In addition, due to the structure symmetry of the used metal cross, the metasurface exhibits polarization-selective excitation of two separate magnetic quadrupolar modes at 37.3 THz and 42.3 THz for the electric field along four symmetry axes of the structure. Our demonstrated distinctive magnetic quadrupolar resonance offers an alternative mode design in plasmonic metamaterials with an improved quality factor, which could be beneficial for metamaterial applications in sensing, optical filtering and infrared emission manipulation etc.