Structural Characterization of Graphite Analogue BC Synthesized Under Various Conditions and Its Application to Ti Intercalation.

A graphite-like material boron carbide (BC) was synthesized under various heat treatment conditions and extensively characterized. First, we synthesized the BC precursor phase by a single-step reaction using a mixed solution of BBr and CH. We confirmed that the precursor phase had a graphite-like structure with B-C chemical bonds, but its crystallinity was poor.

Origin of Unexpected Ir in a Superconducting Candidate SrIrO System Analyzed by Photoelectron Holography.

The reason for the absence of superconductivity in SrIrO was estimated by photoelectron spectra and photoelectron holograms. The analysis of the La photoelectron hologram concluded that La atoms are substituted to Sr sites. Two O 1s peaks were observed and were identified as the oxygens in the IrO and SrO planes by photoelectron holography and density functional theory (DFT) calculations.

Semiconductor-metal transition in BiSe caused by impurity doping.

Doping a typical topological insulator, BiSe, with Ag impurity causes a semiconductor-metal (S-M) transition at 35 K. To deepen the understanding of this phenomenon, structural and transport properties of Ag-doped BiSe were studied. Single-crystal X-ray diffraction (SC-XRD) showed no structural transitions but slight shrinkage of the lattice, indicating no structural origin of the transition.

Superconductivity in BiSbTeSe(= 1.0 and= 2.0) under pressure.

The crystal structure of BiSbTeSe(BiSbTeSe(= 1.0 and= 2.0)) at 0-29 GPa is investigated through synchrotron x-ray diffraction (XRD) and two structural phase transitions are discovered.

Momentum-Dependent Magnon Lifetime in the Metallic Noncollinear Triangular Antiferromagnet CrB_{2}.

Noncollinear magnetic order arises for various reasons in several magnetic systems and exhibits interesting spin dynamics. Despite its ubiquitous presence, little is known of how magnons, otherwise stable quasiparticles, decay in these systems, particularly in metallic magnets. Using inelastic neutron scattering, we examine the magnetic excitation spectra in a metallic noncollinear antiferromagnet CrB_{2}, in which Cr atoms form a triangular lattice and display incommensurate magnetic order.

Superconducting behavior of a new metal iridate compound, SrIr, under pressure.

Herein, we investigated the pressure dependence of electric transport in a new type of superconducting metal iridate compound, SrIr, that exhibits a superconducting transition temperature, T , as high as 6.6 K at ambient pressure, in order to complete the T -pressure (p ) phase diagram. Very recently, this sample's superconductivity was discovered by our group, but the superconducting behavior has not yet been clarified under pressure.

Towards higher-T superconductors.

New superconductors discovered in the Akimitsu laboratory are reviewed here. These materials can be categorized into two groups:1) Cu-oxide superconductors.1-1 Cu-oxide system having CuO planes.

Determination of the local structure of SrMIrO (M = K, La) as a function of doping and temperature.

The local structure of correlated spin-orbit insulator Sr2-xMxIrO4 (M = K, La) has been investigated by Ir L3-edge extended X-ray absorption fine structure measurements. The measurements were performed as a function of temperature for different dopings induced by substitution of Sr with La or K. It is found that Ir-O bonds have strong covalency and they hardly show any change across the Néel temperature.

The electronic structure of AgSnSe (x = 0.0, 0.1, 0.2, 0.25 and 1.0).

We have studied the valence electronic structure of AgSnSe (x = 0.0, 0.1, 0.

Unconventional superconductivity in Y5Rh6Sn18 probed by muon spin relaxation.

Conventional superconductors are robust diamagnets that expel magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high-temperature superconductors, but their identification remains experimentally controversial.

Effect of the counter-anion on the spin-transition properties of a family of Fe(II) tetrazole complexes, [Fe(i4tz)6]X2 (X = ClO4-, PF6-, SbF6-, BF4-).

The monodentate ligand 1-isobutyl-1H-tetrazole (i4tz) was used to synthesize a series of iron(II) spin-crossover (SCO) complexes with the general formula [Fe(i4tz)6]X2, where X = ClO4(-) (1), PF6(-) (2), SbF6(-) (3), or BF4(-) (4). Upon cooling, magnetic susceptibility measurements of compounds 1, 2 and 3 show a reversible one-step spin crossover (SCO) behaviour between HS (S = 2) and LS (S = 0) states without hysteresis. The ClO4(-) compound shows a gradual spin transition at T(1/2) = 208 K at a considerably higher temperature than the other compounds.

Superconductivity in heavily boron-doped silicon carbide.

The discoveries of superconductivity in heavily boron-doped diamond in 2004 and silicon in 2006 have renewed the interest in the superconducting state of semiconductors. Charge-carrier doping of wide-gap semiconductors leads to a metallic phase from which upon further doping superconductivity can emerge. Recently, we discovered superconductivity in a closely related system: heavily boron-doped silicon carbide.

Superconductivity in carrier-doped silicon carbide.

We report growth and characterization of heavily boron-doped 3C-SiC and 6H-SiC and Al-doped 3C-SiC. Both 3C-SiC:B and 6H-SiC:B reveal type-I superconductivity with a critical temperature =1.5 K.