Strong Magnetic Plasmon Resonance in a Simple Metasurface for High-Quality Sensing

We present a simple metasurface consisting of a periodic array of two closely spaced Ag nanowires standing on Ag substrate, to achieve a very strong magnetic plasmon (MP) resonance. We show that the strong MP resonance in the simple metasurface is essentially an antisymmetric resonance caused by the near-field plasmon hybridization in the pair of metallic nanowires. The magnetic field intensity and the spectral linewidth of the MP resonance can be effectively tuned by changing the height of nanowires and the spacing between the two closely spaced nanowires. More importantly, owing to the huge magnetic field enhancement, the ultra-narrow linewidth and the nearly-zero reflection at the strong MP resonance, the metasurface has very high sensitivity (S = 750 nm/RIU, S
_*
= 45/RIU) and figure of merit (FOM = 94, FOM
_*
= 750000). The results suggest that the proposed simple metasurface may find great potential applications in label-free biosensing.