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26 results on '"Ueta, Ikuo"'

5. Superconductivity and its Enhancement under High Pressure in 'F-free' Single Crystals of CeOBiS$_2$

Author

Tanaka, Masashi, Nagao, Masanori, Matsumoto, Ryo, Kataoka, Noriyuki, Ueta, Ikuo, Tanaka, Hiromi, Watauchi, Satoshi, Tanaka, Isao, and Takano, Yoshihiko

Subjects
Condensed Matter - Superconductivity
Abstract

"F-free" CeOBiS$_2$ single crystals have successfully grown, thoroughly eliminating a concern about F-contamination by using a high-purity CsCl flux. The obtained crystals have a plate-like shape with a size of 1.0-3.0 mm in the well-developed plane. Single crystal X-ray structural analysis clearly revealed that the CeOBiS$_2$ crystallizes with a space group $P4/nmm$ (with lattice parameters of $a$ = 4.0189(6) {\AA}, $c$ = 13.573(2) {\AA}). The bond valence sum estimation and X-ray photoelectron spectroscopy analysis showed that the chemical state of Ce was in the mixed valence of Ce$^{3+}$ and Ce$^{4+}$. The single crystals show superconductivity with zero resistivity at $\sim$1.3 K. This is the first conclusive evidence of superconductivity driven by Ce valence fluctuation in surely non-doped CeOBiS$_2$. The superconducting transition temperature was enhanced up to $\sim$3.8 K by applying hydrostatic pressure., Comment: 27 pages, 8 figures, J. Alloys and Compd. (2017)

Published
2017
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6. Superconductivity in CeOBiS2 with cerium valence fluctuation

Author

Nagao, Masanori, Miura, Akira, Ueta, Ikuo, Watauchi, Satoshi, and Tanaka, Isao

Subjects
Condensed Matter - Superconductivity
Abstract

Resistivities of single-crystalline as well as poly-crystalline samples of CeOBiS2 without fluorine doping were measured at temperatures down to 0.13 K, and were compared with those of poly-crystalline LaOBiS2 and PrOBiS2. Both poly-crystalline and single-crystalline CeOBiS2 exhibited zero resistivity below 1.2 K while poly-crystalline LaOBiS2 and PrOBiS2 did not show zero resistivity down to 0.13 K. Superconducting transition temperature of CeOBiS2 was reduced by increasing the applied current density. The superconductivity of CeOBiS2 without chemical doping is likely triggered by the carriers induced by the valence fluctuation between Ce3+ and Ce4+., Comment: 19 pages, 5 figures in Solid State Communications 2016

Published
2016
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