arXiv subjects

Toshio Kamiya

Publications and source records attributed to Toshio Kamiya.

43 records · Page 3Linked to original sources

arXiv2009

Water-induced superconductivity in SrFe2As2

It has been considered that FeAs-based high transition temperature (high-Tc) superconductors need electron or hole doping by aliovalent ion substitution or large off-stoichiometry in order to induce superconductivity. We report that exposure of undoped SrFe2As2 epitaxial thin films to water vapor induces a superconducting transition. These films exhibit a higher onset-Tc (25 K) and larger magnetic field anisotropy than those of cobalt-doped SrFe2As2 epitaxial films, suggesting that the mechanism for the observed superconducting transition differs from that of the aliovalent-ion doped SrFe2As2. The present finding provides a new approach to induce superconductivity with a higher Tc in FeAs-based superconductors.

cond-mat.supr-con↗

arXiv2008

Heteroepitaxial growth and optoelectronic properties of layered iron oxyarsenide, LaFeAsO

Epitaxial thin films of LaFeAsO were fabricated on MgO (001) and mixed-perovskite (La, Sr)(Al, Ta)O3 (001) single-crystal substrates by pulsed laser deposition using a Nd:YAG second harmonic source and a 10 at.% F-doped LaFeAsO disk target. Temperature dependences of the electrical resistivities showed no superconducting transition in the temperature range of 2-300 K, and were similar to those of undoped polycrystalline bulk samples. The transmittance spectrum exhibited a clear peak at ~0.2 eV, which is explained by ab-initio calculations.

cond-mat.supr-con↗

arXiv2008

Superconductivity in Epitaxial Thin Films of Co-Doped SrFe2As2 with Bilayered FeAs Structures and their Magnetic Anisotropy

Superconducting epitaxial films of Fe-based layered arsenide, Co-doped SrFe2As2, were grown at 700oC on mixed perovskite (La, Sr)(Al, Ta)O3 (001) single-crystal substrates by pulsed-laser deposition. Both the epitaxial film and an (001)-oriented film grown at 600oC exhibited superconducting transitions at ~ 20 K. The zero-resistance states of the epitaxial film were sustained under a magnetic field (H) of 9 T at 9 K when H was parallel to the c-axis, while they were sustained at higher temperatures up to 10 K for H parallel to the a-axis. This is the first demonstration of superconducting thin films of FeAs-based new superconductors.

cond-mat.supr-con↗

arXiv2008

Itinerant Ferromagnetism in layered crystals LaCoOX (X = P, As)

The electronic and magnetic properties of cobalt-based layered oxypnictides, LaCoOX (X = P, As), are investigated. LaCoOP and LaCoOAs show metallic type conduction, and the Fermi edge is observed by hard x-ray photoelectron spectroscopy. Ferromagnetic transitions occur at 43 K for LaCoOP and 66 K for LaCoOAs. Above the transition temperatures, temperature dependence of the magnetic susceptibility follows the Curie-Weiss law. X-ray magnetic circular dichroism (XMCD) is observed at the Co L2,3-edge, but not at the other edges. The calculated electronic structure shows a spin polarized ground state. These results indicate that LaCoOX are itinerant ferromagnets and suggest that their magnetic properties are governed by spin fluctuation.

cond-mat.str-el↗

arXiv2008

Nickel-based layered superconductor, LaNiOAs

Rietveld analysis of the powder X-ray diffraction of a new layered oxyarsenide, LaNiOAs, which was synthesized by solid-state reactions, revealed that LaNiOAs belongs to the tetragonal ZrCuSiAs-type structure (P4/nmm) and is composed of alternating stacks of La-O and Ni-As layers. The electrical and magnetic measurements demonstrated that LaNiOAs exhibits a superconducting transition at 2.4 K, and above this, LaNiOAs shows metallic conduction and Pauli paramagnetism. The diamagnetic susceptibility measured at 1.8 K corresponded to ~20% of perfect diamagnetic susceptibility, substantiating that LaNiOAs is a bulk superconductor.

cond-mat.supr-con↗

arXiv2008

Nickel-based phosphide superconductor with infinite-layer structure, BaNi2P2

Analogous to cuprate high-Tc superconductors, a NiP-based compound system has several crystals in which the Ni-P layers have different stacking structures. Herein, the properties of BaNi2P2 are reported. BaNi2P2 has an infinite-layer structure, and shows a superconducting transition at ~3 K. Moreover, it exhibits metallic conduction and Pauli paramagnetism in the temperature range of 4-300 K. Below 3 K, the resistivity sharply drops to zero, and the magnetic susceptibility becomes negative, while the volume fraction of the superconducting phase estimated from the diamagnetic susceptibility reaches ~100 vol.% at 1.9 K. These observations substantiate that BaNi2P2 is a bulk superconductor.

cond-mat.supr-con↗

arXiv2008

Electromagnetic properties and electronic structure of iron-based layered superconductor LaOFeP

Structural, electronic, and magnetic properties of undoped and aliovalent-ion (Ca, F)-doped LaOFeP, which undergo superconducting transitions at transition temperatures (Tc) 4-7 K [Kamihara et al, J. Am. Chem. Soc. 128, 10012, (2006)], were investigated. Tc of the samples varied from 2.4 to 5.5 K in the undoped samples, and was increased up to ~7 K by Ca- and F-doping. The Tc increases are correlated with a decrease in the lattice volume. LaOFeP exhibits paramagnetism in the normal conducting state. Photoemission spectroscopy combined with first-principle band calculations clarified that Fe 3d (dz2 + (dxz, dyz)) orbitals hybridized with P 3p to form a Fermi surface. The band calculations also suggest that the 3d electron of the Fe in LaOFeP is basically in the low-spin configuration, and that the spin moment of LaOFeP is almost quenched, leading to the paramagnetism of the itinerant electrons.

cond-mat.supr-con↗