Electromagnetic metamaterials are artificial materials comprising subwavelength elements made of metals or other materials. They enable us to synthesize qualitatively new media which cannot be realized with conventional materials. The basic theory of wave propagation in metamaterials is presented in order to understand extraordinary phenomena such as negative refractivity and nonreflection propagation. As examples of metamaterial devices, we describe the principles of operation of perfect lenses, invisibility cloaks, and hyperlenses.

Structured metals including wire grids and frequency-selective surfaces have been used as optical devices such as polarizers and filters in the terahertz region. Metamaterials in this frequency region can be fabricated by existing techniques since the sizes of constituent elements of metamaterials are several tens of microns, and the study of terahertz metamaterials has recently become active. In this review, we introduce the recent development and possible applications of metal hole arrays, which are plasmonic crystals, split-ring-resonator metamaterials and dielectric-cube metamaterials.

Recently, many research groups are performing experimental, as well as theoretical, studies on ultrashort and ultrahigh-intensity laser-driven particle sources. In this report, the author describes mainly original results including how to make a desired laser plasma for particle acceleration, the acceleration mechanisms, and the properties of the accelerated particles. The author also briefly describes an actual collaboration with medical professionals including a joint experiment using the particle beam for real therapy.

In this paper, we focus our attention on left-handed metamaterials in microwave regions. Metamaterials with drive-frequency tunability are particularly discussed. We report our experimental and numerical studies toward the realization of tunable left-handed metamaterials using ferromagnetic-metal nanocomposites.

In the recent decade, the efficiency of thermoelectric power generation has been improved using metamaterials with artificial physical properties. One of the key technologies for the enhancement of efficiency is the artificial reduction of thermal conductivity. In this report, we introduce our research on the reduction of phonon transport and molecular dynamics calculations of metamaterials for heat conduction. We also introduce experimental works on heat conduction of thermoelectricity.

The control of light polarization is a key technology in modern photonics, including applications to the optical manipulation of quantum　information and ultrafast optical communication technology. Optical activity is the rotation of the polarization plane of propagating light in a chiral medium independently of the polarization direction of incident light, and this effect is usually small in chiral materials in nature. Recently, polarization control with artificial chiral structures has attracted attention. We have demonstrated that optical activity in the zeroth-order transmission is extraordinarily enhanced in metal or dielectric chiral nanogratings. We show the recent progress of our research in this article.

The interaction between ultra-intense fields and electrons is expected to be much different from a simple elastic scattering between photons and electrons. Recent developments in laser technology allow us to study the behavior of electrons under such an intense field. In this article, as an example of an application of lasers to particle physics, we discuss the feasibility of exploring the structure of space-time via interactions between electrons and intense lasers.

To find the optimal solution from an enormous number of options in choosing materials and device structures for next-generation metal-oxide-semiconductor devices, we have developed a quantum transport simulator based on the nonequilibrium Green's function method.

The lithium-ion battery is a promising power source for devices such as electric vehicles. Extensive efforts are devoted to the development of advanced positive electrode materials. Here, we introduce a recent study on the charge-discharge mechanism of a high-capacity positive electrode material, Li_1.2Mn_0.4Fe_0.4O₂, by analytical transmission electron microscopy. Scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) analyses revealed that both Fe-substituted Li₂MnO₃ and Mn-substituted α-LiFeO₂ nanodomains coexist in single Li_1.2Mn_0.4Fe_0.4O₂ particles. We also observed the difference in extraction and insertion -behaviors of Li ions in both nanodomains at each stage of the first charge-discharge process. We detect an effect of the chemical nanodomain structure, where the two nanodomains share a common anionsublattice coherently, in activating both nanodomains. It was found that the charge compensation by oxygen ions brings about the high-charge capacity. This knowledge should be a key in designing advanced positive electrode materials.

To avoid “electrode problems” in conductance measurements of nanostructured matter, a novel contactless method, in which deep inner shell excitation and the following decay processes are utilized, has been devised. The method is applied to Ar clusters, in each of which a Kr atom that absorbs X-ray photons is embedded, and to aromatic molecules, in each of which a Br atom acts as an X-ray absorbing atom. The decay processes are investigated by photoelectron-photoion-coincidence spectroscopy and multi-ion coincidence momentum imaging. The insulating nature of rare-gas clusters and the conductive nature of aromatic molecules are experimentally confirmed.

After the discovery of MgB₂ with the highest T_c among intermetallic superconductors, its unusual physical property of “two-gap (two-band) superconductivity” and its application to superconducting wires have been performed. This discovery has had a tremendous impact academically and industrially and the progress in its research in the eight years after its discovery is extraordinary. In this article, we report on the development and application of the superconductor MgB₂, together with the recent trend of research on its basic physical properties, and the development of superconducting wires.

Lidar is an effective method for monitoring the atmospheric environment of the upper air from the ground. In this paper, lidar is summarized and the measurement of atmospheric pollutant concentrations in the upper air by differential absorption lidar is described.