Abstract
We theoretically study the plasmonic coupling between magnetic plasmon resonances (MPRs) and propagating surface plasmon polaritons (SPPs) in a three-dimensional (3D) metamaterial consisting of vertical Au split-ring resonators (VSRRs) array on Au substrate. By placing the VSRRs directly onto the Au substrate to remove the dielectric substrates effect, the interaction between MPRs of VSRRs and the SPP mode on the Au substrate can generate an ultranarrow-band hybrid mode with full width at half maximum (FWHM) of 2.2 nm and significantly enhanced magnetic fields, compared to that of VSRRs on dielectric substrates. Owing to the strong coupling, an anti-crossing effect similar to Rabi splitting in atomic physics is also obtained. Our proposed 3D metamaterial on a metal substrate shows high sensitivity (S = 830 nm/RIU) and figure of merit (FOM = 377), which could pave way for the label-free biomedical sensing.
Highlights
Plasmonic and metamaterial structures allow the coherent oscillations of free electrons, known as surface plasmons [1,2,3]
The ultranarrow reflection dip with its full width at half maximum (FWHM) of 2.2 nm arises from the hybridization of propagating surface plasmon polaritons and magnetic resonances
The Fano-like transmission window is weak and the bandwidth is much broader than the reflection dip II of Au vertical Au split-ring resonators (VSRRs) on Au substrate because of the reduced dielectric substrate effect
Summary
Plasmonic and metamaterial structures allow the coherent oscillations of free electrons, known as surface plasmons [1,2,3]. Metamaterial composed of periodic arrays of sub-wavelength metallic split-ring resonators (SRRs) with the capability of enhancing magnetic field has been developed to give rise to novel electromagnetic properties and potential applications such as optical nonlinearity and magnetic biosensors [19,20,21,22,23,24]. The magnetic resonance of the conventional planar SRRs usually has a relatively broad bandwidth and a relatively weak enhancement of electromagnetic fields due to the fast radiation damping [25]. One effective method to enhance magnetic fields of the magnetic resonance and narrow the broad bandwidth is through coupling the MP resonance to other optical narrow-band resonance modes with high-quality factors, such as surface lattice resonances [26,27,28], Fabry-Perot cavity resonances [29,30], optical waveguide mode [31,32], or Tamm plasmons [33,34]
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