It seems that sugar and magnets have little in common, however, this study reveals that a micro-sized sugar cube with a red-colored facet "looks" to circularly polarized light like a magnet.

We prepared non-magnetic double-layer films consisting of a form of sugar, called glucose, and a red-colored dye, called rhodamine, then we studied the absorption of circularly polarized light in the visible region. Surprisingly, the result was very similar not to that of sugar but to that of a magnet even though we did not apply any magnetic fields. [33]

The key to this curious similarity is a symmetry breaking -- the interface between transparent chiral and absorptive achiral media in the double-layer films is essential. Thus, we call this a "chiral meta-interface", in which "meta" means "beyond" or "higher". The chiral meta-interface will pave the way for exploring new optical phenomena.

More recently, we found a novel route to a "one-way mirror" using an artificial molecule -- metamolecule -- with a simultaneous break in time-reversal and space-inversion symmetries.

The metamolecule consists of a Cu helix round a magnetic ferrite rod, which mimics chirality as being coupled to magnetism in microwave regions. This results in directional anisotropy, called magnetochiral effects, of microwaves under a weak static magnetic field. The directional difference of refractive indices by the effect of the metamolecule is several orders of magnitude larger than previous studies of natural materials. [35]

Thanks to the simplicity of the molecular structure, the effects can be enhanced by using resonances and making a metamaterial with the metamolecules. Such metamaterials enable us to realize Lorentz force on light and a one-way mirror. The achievement of this work significantly advances the physics of optics, multiferroic phenomena, and metamaterials.

Related publications: [35], [33], [32], [P13], [P11]

Evanescent waves of light can convey information of sub-wavelength structures, for example, nanoparticles, polymers, or proteins, but usually decay exponentially. So, how can we transport the evanescent waves of light for long distance? This is one of the important questions for the metamaterial superlens that enables us to realize sub-wavelength imaging beyond the diffraction limit.

In order to answer the question, we carried out experimental and numerical studies of resonant photon transport through multilayers consisting of silver and insulator. We have clearly demonstrated that the complex, at times, interplay between various electromagnetic modes including surface plasmon polaritons in the metal-insulator-metal (MIM) system is important to obtain large tunneling probabilities over relatively large distances approaching the wavelength. [26]

Moreover, this study suggests that a possible application of plasmonic MIM structures will be a novel type of hyperlens, which converts evanescent waves to propagating waves of light.

More recently, enhancement of light-matter interaction of a quantum emitter with subwavelength quasiperiodic metamaterials is proposed and demonstrated.

The quasiperiodic metamaterials consist of subwavelength metal-dielectric multilayers, which are arranged into a Fibonacci lattice. The influence of Fibonacci metamaterials (FM) on the dipole emission is analyzed with a semiclassical model. The local density of states near FM is evaluated and a characteristic mode in higher wave numbers is revealed; a strong enhancement of the decay rate was predicted. A lifetime measurement is carried out and a reduction of lifetime of quantum dots on the surface of FM is observed. The enhancement of light-matter interaction arises from the localized latticelike state inherent for self-similar quasiperiodic order. [34]

Related publications: [34], [26], [21]

The electromagnetic responses of materials are determined by electric permittivity and magnetic permeability. Materials with both permittivity and permeability negative are called left-handed materials (LHMs). They are theoretically predicted to show extraordinary electromagnetic responses. However, the LHMs have not been found in nature.

We are now attempting to realize the Left-Handed Meta-Materials (LHMMs) by using ferromagnetic-metal nanocomposite films. The results are expected to open a way to a new paradigm of electromagnetism of matter, making a significant breakthrough in materials science and technology.

Related publication: [24],[19],[15],[13]
[Slide PDF]

Related publications:[17],[16]

Films consisting of metal nanoparticles embedded in matrices are called "metal nanocomposite films" (or "metal nanogranular films"). We are now developing novel techniques to prepare tailor-made metal nanocomposite films. In particular, much effort has been paid to tune the particle size and particle density (volume fraction) independently.

Related publications: [18],[15],[14],[13],[7],[6],[4],[3],[2]

Carbon onion, which is one of the new members of the fullerene family, consists of concentric curved graphitic sheets. We prepared spherical and polyhedral carbon onions in macroscopic quantities by annealing diamond nanoparticles. Structure and electronic properties of the carbon onions have been investigated by high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, electron energy-loss spectroscopy (EELS), and electron spin resonance (ESR). The experimental results strongly suggest that the structure of spherical carbon onions is far from perfectly closed graphitic shells and the sphericity is attributed to imperfect sp² graphitic shells with a number of defects such as sp³-like dangling bonds (a defectiv spherical onion model). pi electrons in spherical onions are thus localized in the small sp² domains and do not act as conduction electrons.

Furthermore, optical extinction properties of the carbon onions were studied in the context of astronomy and astrophysics. We have addressed the contribution of the defective onions to the interstellar extinction bump at 217.5 nm.

Related publications:[P8],[12],[11],[8],[5],[4],[1]