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The addition of a liquid hydrocarbon, xylene, to the starting powder of in-situ powder-in-tube (PIT) processed MgB2 wires was determined to be effective in enhancing the critical current density (Jc) in both high and low magnetic fields. Unlike the addition of SiC nanopowder, which introduces carbon substitution for boron, xylene addition reduced the amount of boron that remained unreacted after the heat treatment and the MgB2 grain size, which resulted in an almost fully-reacted MgB2 core and more flux pinning centers. The addition of both xylene and SiC powder to the starting powder provided a higher Jc than either separate addition to the wire process because both mechanisms associated with xylene and SiC additions work together. For heat treatment at 650 °C, Jc for the xylene added wire achieved 2.2 × 103 A/cm2 at 10 T, which was triple that of the pure sample. The co-added wire had a Jc of 6.3 × 103 A/cm2 at 10 T, which was higher than the SiC added wire, of which Jc was 4.1 × 103 A/cm2 at 10T.

We have fabricated single core superconducting FeTe0.4Se0.6 tapes using a process based on a chemical phase transformation from hexagonal Fe(Te0.4Se0.6)1.4 (non-superconducting) to tetragonal FeTe0.4Se0.6 (superconducting) via an optimal supply of Fe from the Fe sheath by annealing. This process enhanced a packing density of wire core inside the sheath, due to an expansion of the lattice volume via the transformation from high-density hexagonal Fe(Te0.4Se0.6)1.4 to low-density tetragonal FeTe0.4Se0.6. An obvious correlation between annealing temperature (Ta) and phase transformation was observed. Transformation of tape cores from hexagonal to tetragonal were observed above 500 °C. Finally, the hexagonal phase completely transformed into the tetragonal phase by annealing at 600 °C. The obtained superconducting tape showed superconductivity below ∼13.5 K. The magnetic Jc value of 3.0 × 103 A/cm2 at 4.2 K was obtained for the sample prepared by annealing at 525 °C for 3 h followed by annealing at 200 °C for 2 h.

We fabricated FeTe0.5Se0.5 superconducting wires using ex-situ Powder-in-tube method with an Fe sheath. It was amazing that superconducting current was observed in the as-drawn wire without any heat treatments. By heat treatment at 200C for 2 hours, Tczero and Jc at 4.2 K were enhanced up to 9.1 K and 64.1 A/cm2 (Ic = 182.6 mA), respectively. Furthermore, the Jc of FeTe0.5Se0.5 wire heat treated at 200C for 2 hours was not much sensitive to the applied magnetic fields. Therefore, FeTe0.5Se0.5 wires have a great potential for applications., Comment: 15 pages, 5 figures

The superconducting transition temperatures (TC) of (1 1 1) and (0 0 1) boron-doped diamond films deposited by microwave plasma assisted chemical vapor deposition (MPCVD) are investigated in the wide boron concentration range of 1 × 1020 − 1 × 1022 cm−3. The critical boron concentrations of superconductor to insulator transition in (1 1 1) and (0 0 1) films are 3 × 1020 cm−3. TC in (1 1 1) films does not have the tendency to saturate up to 1 × 1022 cm−3, while TC in (0 0 1) films saturates.

Three different cylindrical MgB2 bulk samples were prepared by the underwater shock consolidation method in which shock waves of several GPa, generated by detonation of explosives, were applied to a metallic cylinder containing commercially available MgB2 powders with no additives. Resistivity anisotropy of the samples increased with shock pressure. The highest- and medium-pressure applied samples had finite resistivities in the radial direction for the whole temperature range down to 12 K, whereas their axial and azimuthal resistivities dropped to zero at 32–35 K. By contrast, the lowest-pressure applied sample was approximately isotropic with a normal-state resistivity of ∼40 μΩ cm, an onset temperature of ∼38.5 K, and a transition width of ∼4.5 K. These extremely anisotropic properties would have resulted from the distortion of grain boundaries and grain cores, caused by the shock pressures and their repeated bouncing.

In order to understand the detailed characteristics of YBa 2 Cu 3 O 7− X (YBCO) intrinsic Josephson junctions (IJJs) without shunted grain boundary or non-uniformity, junction area should be reduced to sub-micron region. Hence, we fabricated small-sized IJJs on an YBCO whisker with high-quality crystalline, and investigated their transport properties. The small-sized IJJs, with junction areas of 0.12–0.36 μm 2 , were fabricated by 3D focused ion-beam etching method. We measured current–voltage curves, and showed clear multiple branches with hysteresis structure, such as IJJs in Bi 2 Sr 2 CaCu 2 O 8+ X . Also, from the temperature dependence of critical current, it is found that the junction behavior drastically changes from that of SNS-type to SIS-type when the anisotropy is increased. The critical current densities of junctions were 10–100 kA/cm 2 orders, and they strongly depend on the critical temperature.

We report superconductivity with Tc, onset = ∼10 K in polycrystalline samples of Pr2Ba4Cu7O15 − δ possessing metallic double chains. A reduction treatment on as-sintered samples causes not only the enhanced metallic conduction but also the appearance of superconductivity, in strongly contrast with the oxygen removal effect of superconducting Y2Ba4Cu7O15−δ.

We measured temperature dependence of resistivity under high pressure for oxygen-annealed FeTe 0.8 S 0.2 using piston cylinder cell. With increasing pressure, the zero resistivity temperature ( T c zero ) decreased. Although T c zero was suppressed, intrinsic T c onset gradually increased with increasing pressure. The T c onset was estimated to be ∼13 K at 1.86 GPa from the difference of resistivity caused by suppression of T c onset under magnetic field. This result is different from the result of air exposed FeTe 0.8 S 0.2 . The increase of intrinsic T c onset implies that local area where the T c increases with increasing pressure exists. If FeTe 1− x S x with less excess-Fe concentration could be synthesized, FeTe 1− x S x might show positive pressure effect.

It is important for a new superconducting device application to demonstrate Josephson effect by homoepitaxial all diamond junction. Using only CVD diamond, we have fabricated stacked SNS (superconductor–normal conductor superconductor) Josephson junction where normal state diamond film is sandwiched by superconducting diamond films. The current–voltage (I–V) characteristics of the junction showed clear Josephson properties at 2 K.

The film thickness dependence of Tc in heavily B-doped diamond (1 1 1) and (0 0 1) films was investigated and cross-sectional transmission electron microscope observation was employed to investigate the crystalline structure of heavily B-doped diamond. (1 1 1) films with 5 nm or more and (0 0 1) films with 40 nm or more show superconducting transition. Few dislocations are observed in 500 nm from the interface between the substrate and B-doped homoepitaxial layer in (1 1 1) film and defective structure observed in (0 0 1) film.

The boron concentration dependence of the Si electronic structure of Si(100)2 × 1 surfaces were investigated by angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra exhibit rigid shifts toward lower binding energy as the boron concentration increases. The band dispersion was obtained from fitting procedure, and it is found that the top of the valence band does not exceed the Fermi level even with a boron concentration 35 times larger than the critical concentration of the metal-insulator transition.

We present the first results of Raman scattering with application of magnetic field on magnesium diboride (MgB 2 ). In this work, we have investigated the magnetic field dependence of the 72 meV ( E 2g mode) and the pair-breaking peak around 100 cm −1 which corresponds to σ-band gap. Intensity enhancement of Raman features around 800 cm −1 accompanied with broadening in the line shape of E 2g mode has been observed in some polycrystalline samples at 0 GPa. Results are compared with previous Raman study under hydrostatic pressure.

We report 77 Se-NMR measurements in Co-substituted FeSe, (Fe 0.9 Co 0.1 )Se, which is non-superconducting. Nuclear-spin lattice relaxation rate 1/ T 1 at high temperatures shows that the Co-substitution works as an electron doping. At low temperatures below ∼100 K, the antiferromagnetic fluctuations develop in the pure FeSe, while 1/ T 1 T is a constant even at low temperature in (Fe 0.9 Co 0.1 )Se, indicative of the absence of the strong spin fluctuations. The electron doping is considered to modify the Fermi surface, resulting in the collapse of the nesting in FeSe.

In this paper, we present the result of soft X-ray photoemission spectroscopy and its comparison with the density functional calculation. Although local density approximation seems to be a good starting point for describing the electronic structure of FeSe, the simulated spectrum poorly reproduced the structure around E(B) = 2 eV. This result suggests the necessity of theoretical treatment beyond local density approximation.

11 B magic-angle spinning (MAS) NMR experiments are applied to B-doped diamond samples prepared by high-pressure and high-temperature methods. From the spectrum, we show that there are at least four boron signal components and the one at 28.5 ppm is ascribed to the substitutional boron in the diamond structure providing the carriers responsible for conductivity. We further apply two-dimensional (2D) NMR to examine 1 H dipolar broadening and 11 B– 11 B boron spin diffusion, and candidates purported so far for the excess boron, that is, a boron + hydrogen complex and –B–B– and/or –B–C–B– clusters are negated. Furthermore, we show that 10 B MAS NMR is useful to selectively observe the substitutional boron in the diamond structure appearing at 28.5 ppm, whose quadrupolar coupling is much smaller than that of the excess boron at 65.5 ppm.

Boron-doped carbon nanotubes (CNTs) were synthesized by microwave plasma chemical vapor deposition (MWCVD) method. Obtained CNTs were evaluated by scanning electron microscope (SEM), transmission electron microscope (TEM), and Raman spectroscopy. The results indicated that the CNTs were well crystalline.

We observed dramatic improvement of the superconducting transition temperature in FeTe 0.8 S 0.2 . Although as-grown sample did not show zero resistivity, the sample, which was exposed to air for several days, showed zero resistivity with sharp superconducting transition.

We have performed scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (1 1 1)-oriented epitaxial films of heavily boron-doped diamond at T = 0.47 K. The STM topography shows two kinds of atomic structures: a hydrogenated 1 × 1 structure, C(1 1 1)1 × 1:H, and an amorphous structure. On the C(1 1 1)1 × 1:H region, the tunneling spectra show superconducting property with the energy gap Δ = 0.83 meV. The obtained gap ratio 2 Δ / k B T c = 3.57 is consistent with the weak-coupling BCS theory.