Superconductivity of barium with highest transition temperatures in metallic materials at ambient pressure.

Pressure-induced superconductivity often occurs following structural transition under hydrostatic pressure (P) but disappears after the pressure is released. In the alkali-earth metal barium, superconductivity appears after structural transformation from body-centered cubic structure to hexagonal-close-packed (hcp) structure at P = 5 GPa, and the superconducting transition temperature (T) reaches a maximum of 5 K at P = 18 GPa. Furthermore, by stabilizing the low-temperature phase at P ~ 30 GPa, Tc reached a higher level of 8 K.

Ab initio calculation for electronic structure and optical property of tungsten carbide in a TiCN-based cermet for solar thermal applications.

We present an ab initio calculation to understand electronic structures and optical properties of a tungsten carbide WC being a major component of a TiCN-based cermet. The TiCN-based cermet is widely used as a cutting tool, and is discarded as usual after use. On the other hand, cermet itself is also a famous ingredient of a solar absorption film.

Electronic Correlation Strength of Inorganic Electrides from First Principles.

Strongly correlated electron systems, generally recognized as d- and f-electron systems, have attracted attention as a platform for the emergence of exotic properties such as high-Tc superconductivity. However, correlated electron behaviors have been recently observed in a group of novel materials, electrides, in which s-electrons are confined in subnanometer-sized spaces. Here, we present a trend of electronic correlation of electrides by evaluating the electronic correlation strength obtained from model parameters characterizing effective Hamiltonians of 19 electrides from first principles.

Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain.

Finding a physical approach for increasing the superconducting transition temperature (T) is a challenge in the field of material science. Shear strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large shear strain reduces the grain size and simultaneously expands the unit cells, resulting in an increase in T.

Effect of electron-phonon interactions on orbital fluctuations in iron-based superconductors.

To investigate the possibility of whether electron-phonon coupling can enhance orbital fluctuations in iron-based superconductors, we develop an ab initio method to construct the effective low-energy models including the phonon-related terms. With the derived effective electron-phonon interactions and phonon frequencies, we estimate the static part (ω=0) of the phonon-mediated effective on site intra- or interorbital electron-electron attractions as ∼-0.4  eV and exchange or pair-hopping terms as ∼-0.

Ab initio evidence for strong correlation associated with Mott proximity in iron-based superconductors.

We predict that iron-based superconductors discovered near d(6) configuration (5 Fe 3d orbitals filled by 6 electrons) is located on the foot of an unexpectedly large dome of correlated electron matter centered at the Mott insulator at d(5) (namely, half filling). This is based on the many-variable variational Monte Carlo results for ab initio low-energy models derived by the downfolding. The d(5) Mott proximity extends to subsequent emergence of incoherent metals, orbital differentiations due to the Mott physics, and Hund's rule coupling, followed by antiferromagnetic quantum criticality, in quantitative accordance with available experiments.

Effect of through-space electron transfer on infrared spectrum of amorphous selenium.

In this paper we present theoretical analyses on an infrared (IR) spectrum of amorphous selenium. The system is described by a 216-atom-chain model, and a set of molecular-dynamics simulations is performed to generate vitreous structures and vibrational modes. To describe an electronic structure of the system we employ a complete neglect of differential overlap model parametrized by ab initio cluster calculations.