Chiral Resonance Research Articles

Understanding complex chiral plasmonics.

Chiral nanoplasmonics exhibits great potential for novel nanooptical devices due to the generation of a strong chiroptical response within nanoscale metallic structures. Recently, a number of different approaches have been utilized to create chiral nanoplasmonic structures. However, particularly for tailoring nanooptical chiral sensing devices, the understanding of the resulting chiroptical response when coupling chiral and achiral structures together is crucial and has not been completely understood to date. Here, we present a thorough and step-by-step experimental study to understand the intriguing chiral-achiral coupling scheme. We set up a hybrid plasmonic system, which bears resemblance to the 'host-guest' system in supramolecular chemistry to analyze and explain the complex chiral response both at the chiral and achiral plasmonic resonances. We also provide an elegant and simple analytical model, which can describe, predict, and comprehend the chiroptical spectra in detail. Our study will shed light on designing well-controlled chiral-achiral coupling platforms for reliable chiral sensing.

The combination of high Q factor and chirality in twin cavities and microcavity chain.

Chirality in microcavities has recently shown its bright future in optical sensing and microsized coherent light sources. The key parameters for such applications are the high quality (Q) factor and large chirality. However, the previous reported chiral resonances are either low Q modes or require very special cavity designs. Here we demonstrate a novel, robust, and general mechanism to obtain the chirality in circular cavity. By placing a circular cavity and a spiral cavity in proximity, we show that ultra-high Q factor, large chirality, and unidirectional output can be obtained simultaneously. The highest Q factors of the non-orthogonal mode pairs are almost the same as the ones in circular cavity. And the co-propagating directions of the non-orthogonal mode pairs can be reversed by tuning the mode coupling. This new mechanism for the combination of high Q factor and large chirality is found to be very robust to cavity size, refractive index, and the shape deformation, showing very nice fabrication tolerance. And it can be further extended to microcavity chain and microcavity plane. We believe that our research will shed light on the practical applications of chirality and microcavities.

Enantioselective control of lattice and shape chirality in inorganic nanostructures using chiral biomolecules.

A large number of inorganic materials form crystals with chiral symmetry groups. Enantioselectively synthesizing nanostructures of such materials should lead to interesting optical activity effects. Here we report the synthesis of colloidal tellurium and selenium nanostructures using thiolated chiral biomolecules. The synthesis conditions are tuned to obtain tellurium nanostructures with chiral shapes and large optical activity. These nanostructures exhibit visible optical and chiroptical responses that shift with size and are successfully simulated by an electromagnetic model. The model shows that they behave as chiral optical resonators. The chiral tellurium nanostructures are transformed into chiral gold and silver telluride nanostructures with very large chiroptical activity, demonstrating a simple colloidal chemistry path to chiral plasmonic and semiconductor metamaterials. These materials are natural candidates for studies related to interactions of chiral (bio)molecules with chiral inorganic surfaces, with relevance to asymmetric catalysis, chiral crystallization and the evolution of homochirality in biomolecules.

Extreme optical activity and circular dichroism of chiral metal hole arrays

We report extremely strong optical activity and circular dichroism exhibited by subwavelength arrays of four-start-screw holes fabricated with single-pass focused ion beam milling of freely suspended silver films. Having the fourth order rotational symmetry, the structures exhibit the polarization rotation up to 90° and peaks of full circular dichroism and operate as circular polarizers within certain ranges of wavelengths in the visible. We discuss the observations on the basis of general principles (symmetry, reciprocity, and reversibility) and conclude that the extreme optical chirality is determined by the chiral localized plasmonic resonances.

Preparation, Characterization and Application of Noble-Metal Colloids Stabilized By Chiral Molecules

Gold or platinum colloids stabilized with chiral compounds having a hydroxyl or amino group and multiple carboxylic acids (CHMCA) were prepared by a modified citric-acid method in which L-, D- or DL-tartaric acid, L-, D- or DL-malic acid were used instead of citric acid. Controlling the molar ratio to metal and concentration of CHMCAs and pH of the reaction mixture during the colloid preparation process, CHMCA-stabilized gold or platinum colloids, without giving precipitates even when stored for long time, was successfully prepared. The CHMCA-stabilized gold colloids showed a photoabsorption peak at arou nd 520 nm, corresponding to the particle size of a few tens nanometer, and assigned to the surface plasmon resonance (SPR) and a peak in the circular dichromic spectra in the wavelength region of the SPR absorption though CHMCAs have no absorption there (Fig. 1). These results suggest that CHMCA-modified metal nanoparticles, i.e., "chiral surface plasmon resonance (cSPR)" depending on adsorption rotation direction of circularly polarized light. Application of the gold and platinum colloids loaded onto e.g., titania particles, to catalysis and photocatalysis using cSPR is discussed.

UNIFIED DISPERSIVE APPROACH TO γ* → γππ AND γγ → ππ

A representation of the amplitude γ*(q2) → γππ is proposed which combines large Nc chiral resonance Lagrangian modelling with general unitarity and analyticity properties. The amplitude is constrained from γγ scattering results and e+e− → γπ0π0 measurements by the CMD-2 and SND collaborations. As an application, the contribution of the ππ + γ states in the HVP contribution to the muon g - 2 are reconsidered, taking into account the effect of the strong S-wave ππ rescattering in a model independent way.

Compact negative‐epsilon stop‐band structures based on double‐layer chiral inclusions

Here the authors propose to use electrically excited compact chiral resonators in microstrip configurations for realisation of weakly-radiating stop-band transmission lines. The fundamental resonant mode of these resonators can be excited by both electric and magnetic fields applied parallel to the spiral axis. The authors propose to use a racemic arrangement of an equal amount of left- and right-handed chiral particles between the ground plane and the signal strip and orient the particles so that they are excited by the electric field of the microstrip line. The advantage of this configuration (in addition to strong coupling and weak radiation from excited particles) is that the ground plane can be preserved from being etched (continuous ground structure). The other advantage is that the size of negative permittivity lines loaded with chiral particles can be made very small compared to previous implementations based on complementary split-ring resonators. The circuit models with properly extracted parameters accurately describe the behaviour of both negative permittivity and double-negative lines loaded with electrically coupled resonators. This parameter extraction technique is based on the comparison between the simulated (or measured) transmission and reflection characteristics of the host line loaded with such resonators and those obtained from its lumped-element equivalent circuit model.

Giant circular dichroism of a molecule in a region of strong plasmon resonances between two neighboring gold nanocrystals

We report on giant circular dichroism (CD) of a molecule inserted into a plasmonic hot spot. Naturally occurring molecules and biomolecules typically have CD signals in the UV range, whereas plasmonic nanocrystals exhibit strong plasmon resonances in the visible spectral interval. Therefore, excitations of chiral molecules and plasmon resonances are typically off-resonant. Nevertheless, we demonstrate theoretically that it is possible to create strongly enhanced molecular CD utilizing the plasmons. This task is doubly challenging since it requires both creation and enhancement of the molecular CD in the visible region. We demonstrate this effect within the model which incorporates a chiral molecule and a plasmonic dimer. The associated mechanism of plasmonic CD comes from the Coulomb interaction, which is greatly amplified in a plasmonic hot spot. An important feature of the system is anisotropy that results in giant enhancement for the molecular dipoles parallel to the dimer axis. The proposed effect offers very interesting possibilities for enhanced sensing of chiral molecules using visible light.

Application of Chiral Resonance Lagrangian Theories to the Muon $g-2$

We think that phenomenological resonance Lagrangian models, constrained by global fits from low energy hadron reaction data, can help to improve muon g-2 predictions. The main issue are those contributions which cannot be calculated by perturbative means: the hadronic vacuum polarization (HVP) effects and the hadronic light--by--light (HLbL) scattering contribution. I review recent progress in the evaluation of the HVP contribution within the broken Hidden Local Symmetry (HLS) framework, worked out in collaboration with M. Benayoun, P. David and L. DelBuono. Our HLS driven estimate reads a_mu (LO had)=(688.60+\-4.24) 10^{-10} and we find a_mu (theory)= (11 659 177.65 +/- 5.76) 10^{-10}.

Composite chiral metamaterials with negative refractive index and high values of the figure of merit

A composite chiral metamaterial (CCMM) is designed and studied both numerically and experimentally. The CCMM is constructed by the combination of a continuous metallic wires structure and a purely chiral metamaterial (CMM) that consists of conjugated Rosettes. For the CMM, only very small, useful bands of negative index can be obtained for circularly polarized waves. These bands are all above the chiral resonance frequencies because of the high value of the effective parameter of relative permittivity ε. After the addition of the continuous metallic wires, which provide negative permittivity, the high value of ε can be partially compensated. Thus, a negative index band for the left circularly polarized wave that is below the chiral resonance frequency is obtained for the CCMM. At the same time, a negative index band for the right circularly polarized wave that is above the chiral resonance frequency is also obtained. Furthermore, both negative index bands correspond to the transmission peaks and have high values of the figure of merit. Therefore, the CCMM design that is proposed here is more suitable than the CMM for the construction of chiral metamaterials with a negative index.

Searching for a good candidate to perform a chiral nuclear magnetic resonance experiment in disordered phase: A study of 8,9‐difluoro‐P‐hexahelicene

Calculations of nuclear magnetic shielding polarizabilities of the P-hexahelicene and 8,9-difluoro-P-hexahelicene molecules have been accomplished at the CTOCD-DZ2/6-31G(d,p) level. Pseudoscalars of the nuclear magnetic shielding polarizability are the largest reported so far for second-row atoms. The rf voltage generated by the rotating chiral electric polarization, induced by the permanent magnetic dipole moment of the (19)F nuclei of the 8,9-difluoro-P-hexahelicene and by the spectrometer's magnetic field, is predicted to be ≈10 nV, that is, detectable with modern equipments.

Resonance saturation in the odd-intrinsic parity sector of low-energy QCD

Using the large ${N}_{C}$ approximation we have constructed the most general chiral resonance Lagrangian in the odd-intrinsic parity sector that can generate low-energy chiral constants up to $\mathcal{O}({p}^{6})$. Integrating out the resonance fields these $\mathcal{O}({p}^{6})$ constants are expressed in terms of resonance couplings and masses. The role of ${\ensuremath{\eta}}^{\ensuremath{'}}$ is discussed and its contribution is explicitly factorized. Using the resonance basis we have also calculated two QCD Green functions of currents, $⟨VVP⟩$ and $⟨VAS⟩$, and found, imposing high-energy constraints, additional relations for resonance couplings. We have studied several phenomenological implications based on these correlators which provided, for example, a prediction for the ${\ensuremath{\pi}}^{0}$-pole contribution to the muon $g\ensuremath{-}2$ factor: ${a}_{\ensuremath{\mu}}^{{\ensuremath{\pi}}^{0}}=65.8(1.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$.

Biomimetic synthesis of chiral erbium-doped silver/peptide/silica core-shell nanoparticles (ESPN)

Peptide-modified silver nanoparticles have been coated with an erbium-doped silica layer using a method inspired by silica biomineralization. Electron microscopy and small-angle X-ray scattering confirm the presence of an Ag/peptide core and silica shell. The erbium is present as small Er(2)O(3) particles in and on the silica shell. Raman, IR, UV-Vis, and circular dichroism spectroscopies show that the peptide is still present after shell formation and the nanoparticles conserve a chiral plasmon resonance. Magnetic measurements find a paramagnetic behavior. In vitro tests using a macrophage cell line model show that the resulting multicomponent nanoparticles have a low toxicity for macrophages, even on partial dissolution of the silica shell.

Fermion localization and resonances on a de Sitter thick brane

In C. A. S. Almeida, R. Casana, M. M. Ferreira, Jr., and A. R. Gomes, Phys. Rev. D 79, 125022 (2009), the simplest Yukawa coupling $\ensuremath{\eta}\overline{\ensuremath{\Psi}}\ensuremath{\phi}\ensuremath{\chi}\ensuremath{\Psi}$ was considered for a two-scalar-generated Bloch brane model. Fermionic resonances for both chiralities were obtained, and their appearance is related to branes with internal structure. Inspired on this result, we investigate the localization and resonance spectrum of fermions on a one-scalar-generated de Sitter thick brane with a class of scalar-fermion couplings $\ensuremath{\eta}\overline{\ensuremath{\Psi}}{\ensuremath{\phi}}^{k}\ensuremath{\Psi}$ with positive odd integer $k$. A set of massive fermionic resonances for both chiralities is obtained when provided large coupling constant $\ensuremath{\eta}$. We find that the masses and lifetimes of left and right chiral resonances are almost the same, which demonstrates that it is possible to compose massive Dirac fermions from the left and right chiral resonances. The resonance with lower mass has longer lifetime. For a same set of parameters, the number of resonances increases with $k$ and the lifetime of the lower level resonance for larger $k$ is much longer than the one for smaller $k$.

Chiral symmetry and light resonances in hot and dense matter

We present a study of the π π scattering amplitude in the σ and ρ channels at finite temperature and nuclear density within a chiral unitary framework. Meson resonances are dynamically generated in our approach, which allows us to analyze the behavior of their associated scattering poles when the system is driven towards chiral-symmetry restoration. Medium effects are incorporated in three ways: (a) by thermal corrections of the unitarized scattering amplitudes, (b) by finite nuclear-density effects associated to a renormalization of the pion decay constant, and complementarily (c) by extending our calculation of the scalar–isoscalar channel to account for finite nuclear-density and temperature effects in a microscopic many-body implementation of pion dynamics. Our results are discussed in connection with several phenomenological aspects relevant for nuclear-matter and heavy-ion collision experiments, such as ρ mass scaling versus broadening from dilepton spectra and chiral restoration signals in the σ channel. We also elaborate on the molecular nature of π π resonances.

Postsynthetic Modification of Gold Nanoparticles with Calix[4]arene Enantiomers: Origin of Chiral Surface Plasmon Resonance

Gold nanoparticles postsynthetically modified with chiral 1,3-disubstituted diamino calix[4]arene ligands 2a and 2b are shown to exhibit a circular dichroism (CD)-active surface plasmon resonance absorption (SPR) band. Electronic communication between adsorbed ligand and the gold nanoparticle surface is evidenced in an almost 10-fold increase in the ligand molar ellipticity in the pi-pi* transition spectral range when bound to the gold surface relative to free solution. The footprint of ligand on the gold nanoparticle surface at saturation is measured to be 91 A(2) via monitoring the red shift in the SPR band accompanying ligand adsorption. At ligand concentrations above that required for surface saturation, the ellipticity of the band in the SPR spectral range plateaus to a constant value, whereas the ellipticity of the band in the pi-pi* transition spectral range continues to increase in a manner that corresponds to free ligand in solution. This critical observation correlates ligand adsorption and the onset of the CD-active SPR band. On the basis of the packing characteristics of the bulky calixarene ligand, which are controlled by achiral tert-butyl groups, and the postsynthetic nature of nanoaprticle surface modification of 4.7 nm gold cores used in this study, which precludes synthesis of chiral arrangements of gold atoms, a mechanism responsible for the CD-active SPR bands is proposed, which is based upon the influence of the asymmetric center of the chiral adsorbate on the electronic states of the metal nanoparticle core-an explanation supported by the observed interactions between the gold surface and adsorbed ligand.

Periodic arrangements of chiral scatterers providing negative refractive index bi-isotropic media

The main goal of this contribution is to show that periodic arrangements of chiral scatterers can be the basis for the development of three dimensional and isotropic negative refractive index artificial media. Three dimensionality and isotropy are key issues in this context since only three dimensional structures can be properly viewed as a ``medium,'' and only in isotropic media the refractive index is unambiguously defined. The proposed arrangements are cubic lattices of chiral split ring resonators conveniently designed to yield an isotropic behavior. The reported structures are shown to provide a significant frequency band of negative refraction with good matching to free space.

Negative refraction from balanced quasi‐planar chiral inclusions

AbstractThis work proposes a quasi‐planar chiral resonator suitable for the design of negative refractive index metamaterials. It is presented as an analytical model to determine the metamaterial polarizabilities, which is also the basis of a further study of the viability of negative refraction in chiral and racemic arrangements of inclusions made up with the proposed quasi‐planar chiral resonator. The present analysis is expected to pave the way for the design and building of feasible negative refractive index metamaterials whose inclusions can be manufactured by means of standard photo‐etching techniques. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2606–2609, 2007; Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.22736

Observation and modeling of polarized light from scarab beetles

The light reflected from scarab beetles illuminated with unpolarized white light is analyzed ellipsometrically and displayed as the sum of an elliptically polarized spectrum I(p) and an unpolarized spectrum I(u). A chirped stack of chiral resonators, each with a characteristic Bragg wavelength and partial realignment of birefringent material to a fixed axis, is proposed as a model for simulation of both reflection and polarization spectra. Possible mechanisms that effectively eliminate impedance mismatch at the air-elytron interface and allow some beetles to exhibit nearly perfect circularly polarized reflections are discussed. Results are presented for three representative beetles, Ischiosopha bifasciata, which is shown to be a narrowband left-circular polarizer; Chrysophora chrysochlora, a broadband left-circular polarizer; and Chrysina woodi, an elliptical polarizer. The methods that are developed are applicable to the more general problem of synthesis of reflectors with prescribed reflection and polarization spectra.

Vanishing chiral couplings in the large-NCresonance theory

The construction of a resonance theory involving hadrons requires implementing the information from higher scales into the couplings of the effective Lagrangian. We consider the large-${N}_{C}$ chiral resonance theory incorporating scalars and pseudoscalars, and we find that, by imposing LO short-distance constraints on form factors of QCD currents constructed within this theory, the chiral low-energy constants satisfy resonance saturation at NLO in the $1/{N}_{C}$ expansion.