Magnetic field enhancement at optical frequencies through diffraction coupling of magnetic plasmon resonances in metamaterials

Abstract

We studied theoretically the diffraction coupling of magnetic resonances in metamaterials consisting of a planar rectangular array of metal rod pairs with a dielectric spacer. A narrow-band mixed mode was observed due to a strong interaction between magnetic resonances in individual pairs of metal rods and an in-plane propagating collective surface mode arising from the array periodicity. Upon the excitation of this mixed mode, a five-fold enhancement of magnetic field in the dielectric spacer was achieved as compared with the purely magnetic resonance. It was also found that only a collective surface mode with its magnetic field parallel to the array plane could mediate the excitation of such a mixed mode.Metallic nanoparticles exhibit rich optical properties and have many applications because they support surface plasmon (SP) resonances associated with a huge enhancement of electric fields in their vicinity. 1 Due to radiative or nonradiative (absorptive) damping, however, the particle SP resonances usually have a broad bandwidth or short lifetime, which will limit their applications in some cases. Now recent studies have shown that the SP bandwidth could be tuned through interparticle near-field interaction 2,3 or far-field diffraction coupling 4-8 in periodic arrays of metallic nanoparticles. In the later case, a narrow-band plasmon mode near particle SPs was predicted 4,5 and observed experimentally, 6-8 when the array period is close to the particle resonance wavelength. It is well known that the arrangement of metallic nanoparticles into a periodic lattice can give rise to an in-plane propagating collective surface mode (also referred to as lattice resonance), which appears near the Wood anomaly. 9 The narrow-band mode steps from the interaction between a particle SP mode and this type of collective surface mode. 4-9 Because of a narrow bandwidth, such a hybridized plasmon mode is anticipated to find potential applications. For example, it has been used to enhance and direct fluorescent emission in periodic plasmonic nanoantenna arrays. 8 In metamaterials, specially shaped metallic nanoparticles, like split-ring resonators (SRRs) 10 and paired rods 11,12 or nanodisks, 13 can induce a magnetic moment counteracting the external magnetic field and thus produce diamagnetic responses, termed magnetic SP resonances to differentiate them from electric SP resonances observed in usual metallic nanoparticles. These metallic nanostructures have been widely employed as artificial magnetic atoms to fabricate negative-permeability or negative-refractive-index metamaterials 14 with peculiar electromagnetic properties. 15 Although the interactions of electric SP resonances in metallic nanostructures have been extensively studied and well understood, less is known about the interactions of magnetic SP resonances which could result in interesting physical phenomena. 16 Very recently, a classical analog for electromagnetic induced transparency (EIT) observed in a three-level atomic system 17 has been demonstrated in metamate...

Giant Magnetic Field Enhancement in Hybridized MIM Structures

“…3 and H H i 2 = 3554.8 at the higher and lower energy modes respectively, which is a further enhancement of 438% relative to the single HMIM and a total of 796% enhancement relative to a single MIM on a glass substrate structure. Note that the periodicity of the array itself away from the region of the coupling with the SPP, modifies the magnetic near field enhancement in agreement with far-field diffractive coupling results that has been previously studied [10,15]. For example, at the periods of 470 nm and 950 nm, the maximum magnetic near field enhancement is H H i 2 = 1858 and H H i 2 = 1787 respectively.…”

“…The MIM structure (nanosandwich) consists of two metallic strips separated by a dielectric layer. Such structure supports an anti-symmetric mode where the electric field in the two metallic strips oscillates out of phase producing antiparallel currents which combine with the displacement currents in the dielectric gap to form a current loop that produces a magnetic dipole moment in a direction that is opposite to the incident magnetic field [7,10]. This results in a highly enhanced and localized magnetic field in the dielectric layer known as a magnetic hot spot with potential applications in sensors, light matter interaction at weak magnetic fields and negative refractive index materials [3,11].…”

“…Various methods have been used to reduce the radiative damping through coupling the LSP resonance to a narrow resonance mode. Some examples for enhancing the magnetic plasmon resonance include farfield diffractive coupling [10,15], coupling to Bloch surface waves [16], coupling to SPPs [17] and coupling with a photonic microcavity [18,19].…”

Interaction of magnetic resonators studied by the magnetic field enhancement

“…In this paper, an MR of sandwich structure 24 is chosen as an artificial magnetic atom, in which the magnetic resonance caused by a localized plasmon mode supports a strong magnetic-dipole moment 30 and the localization of plasmon strongly relies on the gap of the sandwich structure. In the strongly localized sandwich structure, magnetic dipole-dipole interaction between MRs is overwhelming, and the electric dipole-dipole interaction is neglected although the latter has to be introduced to explain the interaction of SRRs.…”

“…Another is that the quantum-mechanical spin is intrinsic property, whereas the magnetic-dipole moment of MRs is extrinsic property and sensitively changed with the interaction. There are many papers about MRs [22][23][24] and their interaction [25][26][27][28] is studied in terms of resonance frequency and its damping (half the linewidth of the SRR resonance). 20,21 We find that the MFE of interacting MRs can more sensitively vary with the interaction than previous parameters.…”