arXiv subjects

Masanori Nagao

Publications and source records attributed to Masanori Nagao.

46 records · Page 3Linked to original sources

arXiv2013

Growth and superconducting properties of F-substituted ROBiS2 (R = La, Ce, Nd) single crystals

F-substituted ROBiS2 (R = La, Ce, Nd) superconducting single crystals with different F concentration were grown successfully using CsCl/KCl flux. All the obtained single crystals had a plate-like shape with a well-developed ab-plane of 1-2 mm in size. The flux components of Cs, K, and Cl were not detected in the obtained single crystals by electron probe microanalysis. The grown single crystals of F-substituted LaOBiS2 and CeOBiS2 showed superconducting at about 3 K while the Tc of the F-substituted NdOBiS2 exhibited approximately 5 K. The superconducting anisotropy of the single crystals of F-substituted LaOBiS2 and NdOBiS2 was estimated to be 30-45 according to the effective mass model whereas those values were 13-21 for the F-substituted CeOBiS2 single crystals. The F-substituted CeOBiS2 single crystals exhibited magnetic order at about 7 K that apparently coexisted with superconductivity below around 3 K.

cond-mat.supr-con↗

arXiv2013

Structural Analysis and Superconducting Properties of F-Substituted NdOBiS2 Single Crystals

F-substituted NdOBiS2 superconducting single crystals were grown using CsCl/KCl flux. This is the first example of the single-crystal growth of a BiS2-based superconductor. The obtained single crystals had a plate-like shape with a size of 1-2 mm and a well-developed ab-plane. The crystal structure of the grown crystals was determined by single-crystal X-ray diffraction analysis to be the tetragonal space group P4/nmm (#129) with a = 3.996(3) A and c = 13.464(6) A. The chemical formula of the grown crystals was approximately Nd0.98(0.06)O0.7(0.1)F0.3(0.1)Bi0.98(0.04)S2, and Cs, K, and Cl were not detected in the grown crystals by electron probe microanalysis. The grown crystals had a critical temperature of approximately 5 K. The superconducting anisotropy of the single crystals was estimated to be about 30 from the effective mass model and the upper critical field.

cond-mat.supr-con↗

arXiv2012

Inducement of superconductivity in Fe(Te,S) by sulfuric acid treatment

Superconductivity of Fe0.95Te0.85S0.15 was induced and enhanced by immersing the as-grown (non-superconducting) sample into sulfuric acid. Dissolved Fe was detected in the sulfuric acid treatment, indicating that excess Fe was removed from the Fe0.95Te0.85S0.15 sample.

cond-mat.supr-con↗

arXiv2010

Single crystal growth and structural characterization of FeTe1-xSx

We have synthesized single crystals of FeTe1-xSx and investigated the structural and physical properties. The actual S concentration was found to be significantly smaller than the starting nominal value. The solubility limit of S for the Te site for the crystals grown using a self-flux method was estimated to be around 12 %. Although a suppression of antiferromagnetic transition was observed by S substitution, bulk superconductivity was not observed. A phase diagram of as-grown FeTe1-xSx single crystal was established on the basis of the structural and physical properties.

cond-mat.supr-con↗

arXiv2010

Superconductivity in oxygen-annealed FeTe1-xSx single crystal

We investigated the S-doping-driven phase transition from antiferromagnetic to superconducting in FeTe1-xSx single crystals. The partial substitution of Te by S suppresses antiferromagnetism in Fe-square lattice. Superconductivity is induced by oxygen annealing for only FeTe1-xSx in which the long-range magnetic ordering is suppressed. To realize superconductivity in FeTe1-xSx, both S concentration enough to suppress antiferromagnetism and oxygen annealing are required. Anisotropy of superconductivity in oxygen-annealed FeTe0.886S0.114 was estimated to be 1.17.

cond-mat.supr-con↗

arXiv2010

Growth and Anisotropic Properties of RBa_2Cu_3O_x Single-Crystal Whiskers

Single-crystal whiskers of RBa2Cu3Ox (R-123, R = Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) were successfully grown from Sb- or Te-doped precursors with a nominal composition of R1.5Ba2.75-3.00Cu3M0.5Ox (M: Sb,Te). The whiskers were grown parallel to the ab-plane with the following typical dimensions: 2-8 mm in length, 20-80 \mum in width, and 10-30 \mum in thickness. In the case of rare-earth ions (R3+) with a small ionic radius (Dy, Ho, Er, Tm, Yb, and Y), R-123 whiskers were grown from Te-doped precursors. The growths of Y-123 and Ho-123 whiskers were confirmed using both Te-doped and Sb-doped precursors. On the other hand, for rare-earth ions (R3+) with a large ionic radius (Sm, Eu, and Gd), R-123 whiskers were grown only from Sb-doped precursors. Sb and Te were not detected in the grown whiskers by electron probe microanalysis. The anisotropies of R-123 single-crystal whiskers in the flux liquid state were estimated to be 6.0-33 from the angular dependence of their resistivities under various magnetic fields. The anisotropy increased with decreasing superconducting transition temperature.

cond-mat.supr-con↗

arXiv2005

Superconductivity in Polycrystalline Diamond Thin Films

Superconductivity was discovered in heavily boron-doped diamond thin films deposited by the microwave plasma assisted chemical vapor deposition (MPCVD) method. Advantages of the MPCVD deposited diamond are the controllability of boron concentration in a wide range, and a high boron concentration, especially in (111) oriented films, compared to that of the high-pressure high-temperature method. The superconducting transition temperatures are determined to be 8.7K for Tc onset and 5.0K for zero resistance by transport measurements. And the upper critical field is estimated to be around 7T.

cond-mat.supr-con↗

arXiv2005

Advantage on Superconductivity of Heavily Boron-Doped (111) Diamond Films

The superconductivity transition temperatures Tc(onset) of 11.4 K and Tc(offset) of 7.4 K, which are the highest in diamond at present, are realized on homoepitaxially grown (111) diamond films with a high boron doping concentration of 8.4E21 cm-3 (4.7 atomic percent). Tc values of (111) diamond films are more than twice as high as those of (100) films at the equivalent boron concentration. The Tc of boron-doped (111) diamond increases as the boron content increases up to the maximum incorporated concentration and is agrees with the value estimated using McMillan's equation. The advantageous Tc for (111) diamond films is due to the higher carrier concentration which exceeds its boron concentration.

cond-mat.supr-con↗

arXiv2004

Holes in the valence band of superconducting boron-doped diamond film studied by soft X-ray absorption and emission spectroscopy

Carbon- and boron-2$p$ states of superconducting and non-superconducting boron-doped diamond samples are measured using soft X-ray emission and absorption spectroscopy. For the superconducting sample, a large density of hole states is observed in the valence band in addition to the states in the impurity band. The hole states in the valence band is located at about 1.3 eV below the valence band maximum regardless of the doping level, which cannot be interpreted within a simple rigid band model. Present experimental results, combined with the first principles calculations, suggest that superconductivity is to be attributed to the holes in the valence band.

cond-mat.supr-con↗

arXiv2004

Growth of R-123 Phase Single Crystal Whiskers

Single-crystal whiskers of R1Ba2Cu3Ox (R-123, R= La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu) phase have been successfully grown by the Te- and Ca-doping method. The whiskers were grown from precursor pellets at just below their partial melting (peritectic) temperatures. The nominal composition of the R-123 whiskers is R1+uBa2+vCawCu3Ox (u+v+w=0, w>0) with R and/or Ba sites being substituted by Ca. However, the amount of Te was less than the analytical limit. The critical temperatures of the R-123 whiskers were around 80 K, and among these whiskers those with larger R ionic radii such as Dy, Gd, Eu and Sm require post-annealing in an oxygen atmosphere.

cond-mat.supr-con↗