Magnetic Plasmon Resonance Research Articles

The "Recognition Helix" of the Type II Acyl Carrier Protein (ACP) Utilizes a "Ubiquitin Interacting Motif (UIM)"-like Surface To Bind Its Partners.

Interaction interfaces comprise a finite number of sequence/structural motifs, which are often repeated in nature. Here we show how a helical motif present in the acyl carrier protein (ACP), involved in multiprotein interactions, displays a binding interface similar to that of the "ubiquitin interacting motif (UIM)". Analysis of the crystal structures of the ACP-enzyme complexes gave the first hint that helix II of the ACP ("universal recognition helix") utilizes UIM-like noncovalent interactions to associate with the type II fatty acid biosynthesis (FAS) pathway enzymes. The ACP interacting functional surface of the FAS enzymes comprises positively charged residues, flanking a central hydrophobic patch, akin to ubiquitin. Our nuclear magnetic resonance chemical shift perturbation studies, relaxation studies, and surface plasmon resonance measurements unequivocally show that helix II of ACP behaves like a UIM motif in its interactions with ubiquitin, by binding the Ile 44 functional surface of the latter. A synthetic peptide with the ACP helix II sequence showed equivalent binding to ubiquitin. The evolution of similar interaction motifs in the two systems has probably been driven by functional constraints, as both ACP and UIM participate in multiprotein interactions.

Tunable Spectral Ordering of Magnetic Plasmon Resonances in Noble Metal Nanoclusters

Experimental characterization of the optical and magnetic properties of noble metal nanoclusters has exposed a size regime in between single-ring and extended two-dimensional nanocluster networks where the behavior of magnetic plasmon resonances is not well understood. In this intermediate size regime, individual electric dipole plasmons on each nanoparticle within the cluster can hybridize into delocalized magnetic modes that couple to either the electric or magnetic field of light with seemingly arbitrary energy ordering. Here, using a coupled-dipole model that includes fully retarded interactions between electric dipole plasmons, we show that magnetic plasmon resonance energies can be controllably tuned and even made to cross as a function of nanocluster size. Experimental confirmation of this prediction is challenging because optical selection rules dictate the simultaneous excitation of many spectrally overlapping magnetic plasmon modes. However, based on analytic modeling and numerical simulation, w...

Graphene-induced modulation effects on magnetic plasmon in multilayer metal-dielectric-metal metamaterial

Motivated by the increasing interest in active control of the optical response in magnetic metamaterials, we theoretically demonstrate that monolayer graphene, even only a single atom thick, can provide an efficient modulation on the magnetic plasmon (MP) resonance, including over 10 meV resonance shift and over 25% modulation of resonance absorption intensity. We show that the resonance shift is distinctly different from the graphene-induced change in electrically excited surface plasmon resonances in plasmonic systems. Our analysis based on the equivalent nanocircuit method reveals that the MP resonance shift is governed by both the real and imaginary parts of graphene permittivity. Importantly, we find that an additional dissipation channel relevant to the graphene-induced resistance governs the MP absorption and that even the dissipation channel of interband transition is blocked. The interplay between both channels results in a pronounced modification of MP absorption intensities. The findings will offer a promising way to realize the dynamic control of the magnetic response, which holds great potential applications in graphene-based active metamaterials.

Controlling Magnetic Dipole Resonance in Raspberry-like Metamolecules

Raspberry-like metamolecules (RMMs), clusters of closely packed noble metal nanobeads self-assembled on a dielectric core, exhibit emergent optical properties not available in simple nanoparticles. Examples include broad band far-field extinction and artificial optical magnetism. An important feature of these clusters is that their magnetic plasmon resonance and the breadth of their extinction spectra can be tuned via simple synthetic routes, such as by changing the bead size, core size, or the average interbead distance. However, the effect of each of these variables on the final magnetic resonance frequency and strength has not been studied in depth. Understanding how to tune the electric and magnetic resonance modes in these clusters can help improve the design of novel metamaterials for various applications. In this article, we combine theoretical analyses using numerical finite-different time-domain modeling and analytical dipole–dipole coupling theory to study the role of these variables in the glob...

Fragment-Based Discovery of Inhibitors of the Bacterial DnaG-SSB Interaction.

In bacteria, the DnaG primase is responsible for synthesis of short RNA primers used to initiate chain extension by replicative DNA polymerase(s) during chromosomal replication. Among the proteins with which Escherichia coli DnaG interacts is the single-stranded DNA-binding protein, SSB. The C-terminal hexapeptide motif of SSB (DDDIPF; SSB-Ct) is highly conserved and is known to engage in essential interactions with many proteins in nucleic acid metabolism, including primase. Here, fragment-based screening by saturation-transfer difference nuclear magnetic resonance (STD-NMR) and surface plasmon resonance assays identified inhibitors of the primase/SSB-Ct interaction. Hits were shown to bind to the SSB-Ct-binding site using 15N–1H HSQC spectra. STD-NMR was used to demonstrate binding of one hit to other SSB-Ct binding partners, confirming the possibility of simultaneous inhibition of multiple protein/SSB interactions. The fragment molecules represent promising scaffolds on which to build to discover new antibacterial compounds.

Enhanced normal-incidence Goos-Hänchen effects induced by magnetic surface plasmons in magneto-optical metamaterials.

Goos-Hänchen (GH) effects at normal incidence are investigated for metamaterials consisting of an array of ferrite rods. A new effective-medium approach is presented and applied to retrieve the effective parameters of the magneto-optical (MO) metamaterials based on a transformation method. Giant normal-incidence Goos-Hänchen (NIGH) shifts on total reflection and enhanced magnetic switching effects are predicted near magnetic surface plasmon (MSP) resonances for structures with small effective permittivity. Numerical simulations are performed and the results are in good agreement with those from the transformation effective-medium approach.

Magnetodynamic Study of Spin Resonances in Cylindrical and Spherical YIG Samples

Rigorous magnetodynamic (MD) study presented in this paper reveals what seems to be the real nature of ferromagnetic resonances occurring in gyromagnetic samples situated in larger resonant cavities. Experiments were performed with cylindrical and spherical YIG samples inserted into either cylindrical dielectric resonator or typical rectangular cavity. It is shown that the dominant mode present in the YIG sample, which was identified as the $\text {HE}_{111}^{+}$ mode, satisfies the magnetic plasmon resonance condition defined by the effective permeability ${\mu }_{r}\approx {-1}$ for cylindrical samples or ${\mu }_{r}\approx {-2}$ for spherical samples. Experiments confirmed the existence of surface resonances, identified as magnetic plasmons, and volume resonances. Comparison between the MD model, the quasi-magnetostatic model, and the perturbation theory was performed and limitations of the approximate approaches are shown.

Unidirectional edge modes launched by surface fluctuation in magnetic metamaterials

We demonstrate theoretically that the surface fluctuation can be used to launch the unidirectional electromagnetic edge mode for a Gaussian beam incident normal to the magnetic metamaterials (MMs) composed of an array of ferrite rods with the uppermost layer introduced position or size fluctuation in the coupling region. Such an edge mode is solely allowed to propagate in one direction due to the time-reversal symmetry breaking in MMs under the exertion of an external magnetic field, and it is substantially enhanced by the magnetic surface plasmon resonance. The nonreciprocal excitation of the edge states can also be understood by examining the scattering amplitudes of different partial waves, which indicate that the 1st order of the angular momentum channel plays a crucial role in realizing the nonreciprocity. The present research might be significant for the implementation of unidirectional absorption and the reexamination of bound states in the continuum in the context of MMs. In addition, the unique optical property can be exploited to design electromagnetic waveguide devices, such as one-way waveguide and wave bender, which are strongly robust against the obstacles placed in the channel of designed devices, facilitating to realize optical integrated circuits.

Ferromagnetic linewidth measurements employing electrodynamic model of the magnetic plasmon resonance

The mode of uniform precession, or Kittel mode, in a magnetized ferromagnetic sphere, has recently been proven to be the magnetic plasmon resonance. In this paper we show how to apply the electrodynamic model of the magnetic plasmon resonance for accurate measurements of the ferromagnetic resonance linewidth ΔH. Two measurement methods are presented. The first one employs Q-factor measurements of the magnetic plasmon resonance coupled to the resonance of an empty metallic cavity. Such coupled modes are known as magnon-polariton modes, i.e. hybridized modes between the collective spin excitation and the cavity excitation. The second one employs direct Q-factor measurements of the magnetic plasmon resonance in a filter setup with two orthogonal semi-loops used for coupling. Q-factor measurements are performed employing a vector network analyser. The methods presented in this paper allow one to extend the measurement range of the ferromagnetic resonance linewidth ΔH well beyond the limits of the commonly used measurement standards in terms of the size of the samples and the lowest measurable linewidths. Samples that can be measured with the newly proposed methods may have larger size as compared to the size of samples that were used in the standard methods restricted by the limits of perturbation theory.

Giant Magnetic Field Enhancement in Hybridized MIM Structures

We propose numerically an approach to narrow the plasmon linewidth and enhance the magnetic near field intensity at a magnetic hot spot in a hybridized metal–insulator–metal (MIM) structure. First, we insert in part of the dielectric layer of the MIM, at its center, another dielectric material of a high refractive index (HRI). This results in an increase in the magnetic near field enhancement of the magnetic plasmon (MP) resonance by 82% compared with the MIM without the HRI material. We then couple this enhanced MP resonance to a propagating surface plasmon polariton (SPP) to achieve a further enhancement of 438%. The strong coupling between the MP and the SPP is demonstrated by the large anti-crossing in the reflection spectra. The resulting maximum magnetic field enhancement at the gap is $\sim \left |{ {H / {H_{i} }} }\right |^{2}=3555$ .

Enthalpy-Based Screening of Focused Combinatorial Libraries for the Identification of Potent and Selective Ligands.

In modern drug discovery, the ability of biophysical methods, including nuclear magnetic resonance spectroscopy or surface plasmon resonance, to detect and characterize ligand-protein interactions accurately and unambiguously makes these approaches preferred versus conventional biochemical high-throughput screening of large collections of compounds. Nonetheless, ligand screening strategies that address simultaneously potency and selectivity have not yet been fully developed. In this work, we propose a novel method for screening large collections of combinatorial libraries using enthalpy measurements as a primary screening technique. We demonstrate that selecting binders that are driven by enthalpy (ΔH) results in agents that are not only potent but also more selective for a given target. This general and novel approach, we termed ΔH screening of fPOS (enthalpy screening of focused positional scanning library), combines the principles of focused combinatorial chemistry with rapid calorimetry measurements to efficiently identify potent and selective inhibitors.

Magnetic Fano resonance of heterodimer nanostructure by azimuthally polarized excitation.

The optical properties of a Si-Au heterodimer nanostructure, which is composed of an Au split nanoring surrounded by a Si nanoring with a larger diameter, are investigated both theoretically and numerically. It is found that a pure magnetic plasmon Fano resonance can be achieved in the Si-Au heterodimer nanostructure when it is excited by an azimuthally polarized beam. It is revealed that the pure magnetic Fano resonance is generated by the destructive interference between the magnetic dipole resonance of the Si nanoring and the magnetic dipole resonance of the Au split nanoring. A coupled oscillator model is employed to analyze the Fano resonance of the Si-Au heterodimer nanostructure. The pure magnetic response of the Si-Au heterodimer nanostructure is verified by the current density distributions and the scattering powers of the electric and magnetic multipoles. The Fano resonance in the Si-Au heterodimer nanostructure exhibits potential applications of low-loss magnetic plasmon resonance in the construction of artificial magnetic metamaterials.

Magnetic Dipole Scattering from Metallic Nanowire for Ultrasensitive Deflection Sensing.

It is generally believed that when a single metallic nanowire is sufficiently small, it scatters like a point electric dipole. We show theoretically when a metallic nanowire is placed inside specially designed beams, the magnetic dipole contribution along with the electric dipole resonance can lead to unidirectional scattering in the far field, fulfilling Kerker's condition. Remarkably, this far-field unidirectional scattering encodes information that is highly dependent on the nanowire's deflection at a scale much smaller than the wavelength. The special roles of small but essential magnetic response along with the plasmonic resonance are highlighted for this extreme sensitivity as compared with the dielectric counterpart. In addition, the same essential role of the magnetic dipole contribution is also presented for a very small metallic nanosphere.

Ferromagnetic Resonance Revised \u2013 Electrodynamic Approach

Resonance in a ferromagnetic sphere, known in the body of literature as the mode of uniform precession, has recently been proven to be magnetic plasmon resonance (MPR). This finding has prompted research which is presented in this paper on the relation between the Q-factor at the MPR and the ferromagnetic resonance (FMR) linewidth ΔH, which is a parameter of magnetized gyromagnetic materials. It is proven in this paper that ΔH can be unequivocally determined from the Q-factor measured at the MPR, if all losses in the resonance system are properly accounted for. It can be undertaken through a rigorous but simple electrodynamic study involving the transcendental equation, as proposed in this paper. The present study also reveals that electric losses have a substantially reduced impact on ΔH due to the large magnetic to electric energy storage ratio at the MPR. Theoretical results are supported by measurements of the Q-factors on a monocrystalline yttrium iron garnet (YIG) sphere.

High Optical Transmission in a Hybrid Plasmonic-Optical Structure with a Continuous Metal Film

Metals are naturally opaque for electromagnetic (EM) waves below violet frequency due to the Coulomb screening effect. In this letter, we demonstrate high optical transparency of a seamless continuous metal film by sandwiching it in a hybrid plasmonic-optical structure. The proposed structure consists of a plasmonic array and an optical cavity, which exhibits magnetic plasmon (MP) resonance and optical Fabry-Perot (FP) resonance, respectively. An optical transparency of 84% in the near-IR regime is achieved making use of interaction between the plasmonic and optical modes. Furthermore, spectral tunability of the high transparency is demonstrated and robustness under oblique incidence is examined. This work may give insights into plasmonic-optical interactions and may be a potential candidate for transparent electrodes.

Controlling Surface Plasmon Resonance of Metal Nanocap for Upconversion Enhancement

An upconversion composite nanoparticle (NP) composed of an Er and Yb doped Y2O3 (Y2O3:Yb,Er) NP and a Au nanocap was developed, and the effect of the coverage on the optical responses was studied by numerical simulations and optical measurements of single composite NPs. The formation of a composite NP and the control of the coverage were confirmed by transmission electron microscope observations. By controlling the coverage, the scattering peak due to the magnetic dipole surface plasmon resonance shifted from around 700 nm to over 900 nm. The upconversion intensity was also strongly modified by the coverage. Clear correlation was observed between the surface plasmon resonance wavelength and the upconversion intensity; the intensity increased as the resonance wavelength approached the excitation wavelength (975 nm). The largest enhancement factors of the upconversion with respect to that of a Y2O3:Yb,Er NP without a Au nanocap were 64 and 101-fold for the green (∼560 nm) and red (∼660 nm) emissions, respec...

Engineering the magnetic plasmon resonances of metamaterials for high-quality sensing.

We present a powerful method to enhance the magnetic plasmon (MP) resonances of metamaterials composed of periodic arrays of U-shaped metallic split-ring resonators (SRRs) for high-quality sensing. We show that by suspending the metamaterials to reduce the effect of the substrate, the strong diffraction coupling of MP resonances can be achieved, which leads to a narrow-band mixed MP mode with a large magnetic field enhancement. It is also shown that for such a diffraction coupling, the magnetic field component of the lattice resonance mode of periodic arrays must be parallel to the induced magnetic moment in the metallic SRRs. Importantly, the sensitivity and the figure of merit (FOM) of the suspended metamaterials can reach as high as 1300 nm/RIU and 40, respectively. These results suggest that the proposed metamaterials may find great potential applications in label-free biomedical sensing.

Enhanced Magnetic Fields at Optical Frequency by Diffraction Coupling of Magnetic Resonances in Lifted Metamaterials

By lifting metamaterials composed of periodic arrays of metallic nanodisk pairs to reduce the effect of substrate, we demonstrate theoretically the diffraction coupling phenomenon of magnetic plasmon (MP) resonances. A narrow-band hybridized mode is observed owing to the strong interactions between MP resonances in individual pairs of metallic nanodisks and a collective surface mode propagating in the array plane. When the hybridized mode is excited, a 5.6-fold enhancement of magnetic fields in nanodisk pairs is obtained as compared with the purely MP resonance. It is also found that for such a diffraction coupling, the magnetic field of the collective surface mode must be parallel to the magnetic moment induced in the paired metallic nanodisks. Our numerical results may find some promising potential applications, like magnetic nonlinearity and sensors.

Electrodynamic study of YIG filters and resonators.

Numerical solutions of coupled Maxwell and Landau-Lifshitz-Gilbert equations for a magnetized yttrium iron garnet (YIG) sphere acting as a one-stage filter are presented. The filter is analysed using finite-difference time-domain technique. Contrary to the state of the art, the study shows that the maximum electromagnetic power transmission through the YIG filter occurs at the frequency of the magnetic plasmon resonance with the effective permeability of the gyromagnetic medium μr ≈ −2, and not at a ferromagnetic resonance frequency. Such a new understanding of the YIG filter operation, makes it one of the most commonly used single-negative plasmonic metamaterials. The frequency of maximum transmission is also found to weakly depend on the size of the YIG sphere. An analytic electromagnetic analysis of resonances in a YIG sphere is performed for circularly polarized electromagnetic fields. The YIG sphere is situated in a free space and in a large spherical cavity. The study demonstrates that both volume resonances and magnetic plasmon resonances can be solutions of the same transcendental equations.

Boosting figures of merit of cavity plasmon resonance based refractive index sensing in dielectric-metal core-shell resonators.

We theoretically investigate the sensing performance of the dielectric-metal core-shell resonators (DMCSRs) that support multipolar sharp magnetic and electric-based cavity plasmon resonances. We show that at the cavity resonances the ability of the DMCSRs to strongly confine the optical fields inside the cavity is robust against the existence of nano-openings in the metal shell layer. As a result, both the perfect DMCSRs having a complete metal shell layer and the non-perfect DMCSRs with nano-openings in the metal shell layers exhibit high refractive index sensitivities of 700 ~1200 nm/RIU. Furthermore, we demonstrate that such high refractive index sensitivities could be well maintained in an array of interconnected non-perfect DMCSRs. The narrow linewidths of the cavity plasmon resonances coupled with their high index sensitivities make the array of non-perfect DMCSRs possess high figure of merit (FOM) values up to ~88, approaching the theoretically estimated upper limit (FOM ≈108) for gold standard prism coupled surface-plasmon sensors.