Pressure-induced superconductivity in AgxBi2-xSe3

We investigated the pressure dependence of electric transport and crystal structure of Ag-doped Bi2Se3. In the sample prepared by Ag doping of Bi2Se3, the Bi atom was partially replaced by Ag, i.e., Ag0.05Bi1.95Se3. X-ray diffraction patterns of Ag0.05Bi1.95Se3 measured at 0–30 GPa showed three different structural phases, with rhombohedral, monoclinic, and tetragonal structures forming in turn as pressure increased, and structural phase transitions at 8.8 and 24 GPa. Ag0.05Bi1.95Se3 showed no superconductivity down to 2.0 K at 0 GPa, but under pressure, superconductivity suddenly appeared at 11 GPa. The magnetic field (H) dependence of the superconducting transition temperature Tc was measured at 11 and 20.5 GPa, in order to investigate whether the pressure-induced superconducting phase is explained by either p-wave polar model or s-wave model

Cluster Size Effect of X-ray Fluorescence Hologram Simulation Using Sr0.95La0.05TiO3

We simulated La Lγ1 X-ray fluorescence holography (La Lγ1 XFH) on a spherical cluster model of Sr0.95La0.05TiO3. As the radius of the model rc increased from 10 Å to 200 Å, the simulated hologram pattern became finer and sharper. The X-ray standing wave lines in the simulated hologram of the model with rc = 200 Å reproduced those in the experimentally obtained hologram well. Because the X-ray fluorescence hologram is defined as a function on a spherical surface, we estimate the fineness of the pattern by calculating the power spectrum with the spherical harmonics transform. The power spectrum of the holographic oscillations of the experimentally obtained hologram shows no cutoff below the Nyquist frequency. The power spectra of the models with 60 Å ≤ rc ≤ 200 Å do not show cutoffs either. These indicate that the radius of the cluster model rc should be set at least 200 Å to reproduce the experimentally obtained hologram of Sr0.95La0.05TiO3

Local Structure Analysis on Yttria-Stabilized Zirconia by X-ray Fluorescence Holography

Y and Zr Kα X-ray fluorescence holography measurements were carried out on a single crystal of yttria-stabilized zirconia with 13 mol% of yttria at room temperature to investigate the local structures around the impurity Y and host Zr atoms. Around the central Y atom, the images of the surrounding Zr/Y atoms are seen as a face-centered-cubic (fcc) sub-lattice. Thus, the impurity Y atoms are sure to be replaced with the Zr atoms as expected earlier. In addition, strong images are also observed, by which some of the Y atoms are located at the interstitial positions at the center of the fcc lattice. The atomic images around the central Zr atom are very weak, indicating large lattice distortions around the Zr atom. Some images outside of the ideal fcc lattice indicate that the local structures around the Zr atoms are similar to the original pure monoclinic ZrO2, and some of them would be rotated due probably to the interstitial doping of the impurity Y atoms

Three-dimensional Atomic Image of FeSe High-temperature Superconductor by X-ray Fluorescence Holography

Fe Kα X-ray fluorescence holography measurements were carried out at room temperature on an FeSe high-temperature superconductor to clarify the relationship between the local structures around the Fe atoms and the superconducting nature. The obtained three-dimensional atomic arrangements strongly reveal a formation of strong FeSe4 clusters. On the other hand, the Se—Fe—Se bond angle largely spreads, causing a large ambiguity in the chalcogen height and large displacements of the Fe sublattice. Thus, it is reasonable that the tetragonal-to-orthorhombic structural (nematic) transition does not affect the magnetic ordering in the Fe layer