Tetsuyuki Kaneko

Zero-resistance temperature of Tl-based “2223” superconductor increased to 127 K

Abstract It is demonstrated that a single-phase “2223” superconductor, i.e. Tl 1.7 Ba 2 Ca 2.3 Cu 3 O z , exhibits the zero-resistance temperature at 127 K and the diamagnetic onset temperature at 130 K, when the sample is encapsulated in an evacuated quartz tube and post-annealed at 750°C for 250 h. It is found that the encapsulation of the sample is crucially important for post-annealing longer than ∼10 h. Both the zero-resistance temperature and the diamagnetic onset temperature increase as the post-annealing time increases. This suggests that the increase in the superconducting critical temperature is related to a certain diffusion process such as ordering of constituent ions.

A novel scaling of magnetic field dependencies of critical currents for Ag-sheathed Bi-2223 superconducting tape

Abstract Certain characteristics in magnetic field dependences of critical current densities (Jc) for the Ag-sheathed Bi-2223 superconducting tape have been found. One property regards the direction of the magnetic field applied to the tape. Both Jc values in the field, applied parallel and perpendicular to the tape surface, are on an identical curve when the magnitude of field (B), applied parallel to the tape surface, is multiplied by a characteristic coefficient, which relates to the grain alignment of each tape. Another concerns the relationship between Jc and the magnitude of the field. The Jc is expressed by a simple logarithmic function of B (log(B)) from a very low field to a high field. This relation is applicable within a wide temperature range.

Superconductivity of Y1Ba2(Cu1-xFex)3Oy

A systematic study on the superconductivity of Y1Ba2(Cu1-xFex)3Oy has been made down to 30 mK for various x values. The critical temperature decreases linearly with x. The complete Meissner effect is retained down to 30 mK, up to about x=0.10. The crystal structure of the superconducting phase was found to transform from the orthorhombic to the tetragonal between x=0.02 and 0.05. It is concluded that a branching effect of a one-dimensional chain of Cu1-O through Fe impurities is essential for this structure transition. The supercurrent is considered to flow on the two-dimensional sheets of Cu2.

Air-stable p-n junction diodes based on single-walled carbon nanotubes encapsulating Fe nanoparticles

The authors report electrical transport properties of p-n junction based on semiconducting single-walled carbon nanotubes (SWCNTs). The formation of p-n junction is realized in SWCNTs, which are encapsulated with Fe nanoparticles at low filling fractions. The devices exhibit an excellent rectifying behavior, and no current down to 10−14A level flows when the device is biased in reverse. During measurements performed in the temperature range from 10to300K, the devices maintain high reproducibility. More importantly, even after exposure to air, the rectifying characteristic keeps stable, which strongly suggests that ideal p-n junction diodes can be fabricated by SWCNTs.

195Pt Knight Shift in the Heavy Fermion Superconductor UPt3

We observed 195 Pt NMR in UPt 3 in both the normal and superconducting states, The spectrum has a large negative shift and is quite anisotropic. In 5 kOe, no changes in the negative shift were observed down to the temperature of 60 mK, where the system was in the superconducting state. This means that the conduction electron spin susceptibility does not decrease in the superconducting state. The result does not contradict the possibility of anisotropic p-wave superconductivity of UPt 3 .

Development of Ag-sheathed Bi-2223 superconducting wires and their applications

Silver-sheathed multifilamentary BiPbSrCaCuO 2223 superconducting wires with long length and high Jc of over 3/spl times/10/sup 4/ A/cm (77.3 K, 0 T) were developed by using the powder-in-tube method. For future industrial applications, high Jc with high Ic wires, high strength wires and low AC loss wires were also developed for large scale magnet applications and electric apparatus for AC use. In the case of AC conductor, twist effect was investigated in order to reduce the wire AC loss, PVF coating technology was applied to high strength wire. PVF coating technology made it possible to obtain amperage parallel conductor with low AC loss, because each strand is electrically insulated. As a progress of technology, we could fabricate many application prototypes. In the high amperage conductor application, current leads and cable conductors were developed. In the magnet application, pancake magnets cooled by GM refrigerator and operated at around 20 K were developed, We have also developed the transformer as an AC application operated in the liquid nitrogen.

Synthesis and electronic properties of ferrocene-filled double-walled carbon nanotubes

Double-walled carbon nanotubes (DWNTs) are filled with ferrocene molecules by a vapour diffusion method for the first time. The as-synthesized ferrocene-filled DWNTs are characterized by transmission electron microscopy (TEM), energy-dispersive x-ray spectrometry (EDX) and Raman spectroscopy. Electronic properties of double-walled carbon nanotubes (DWNTs) filled with ferrocene molecules are studied by fabricating them as the channels of field-effect transistor (FET) devices. Our results reveal that electronic properties of ferrocene-filled DWNTs are greatly modified due to the charge transfer between ferrocene molecules and DWNTs. In addition, after ferrocene molecules are decomposed inside DWNTs, electronic properties of DWNTs exhibit a further change due to Fe encapsulation, and unipolar n-type semiconducting DWNTs are consequently obtained.

Electronic transport properties of Cs-encapsulated double-walled carbon nanotubes

Electronic transport properties of Cs-encapsulated double-walled carbon nanotubes (DWNTs) synthesized via a plasma irradiation method are investigated by fabricating them as field-effect transistor devices. The authors’ results indicate that Cs-encapsulated DWNTs exhibit a high performance n-type characteristic in contrast to ambipolar behavior of pristine DWNTs. Coulomb blockade oscillations are observed on the Cs-encapsulated DWNTs at low temperatures. In addition, it is found that the semiconducting characteristics of the as-synthesized Cs-encapsulated DWNTs can possibly be controllable by adjusting applied negative dc bias voltages during the plasma synthesis process.

Enhancement of Tc in (Bi,Pb)-2223 superconductor by vacuum encapsulation and post-annealing

Abstract (Bi,Pb)-2223 superconductors with nominal composition Bi1.85Pb0.35Sr2Ca2Cu3.1Oy were synthesized as almost single phase samples, with a Tc onset of 110 K. By applying a vacuum encapsulation and low temperature post-annealing process, Tc onset increased to 115 K, and Tc zero exceeded 110 K. If samples were encapsulated in an oxygen atmosphere, Tc did not enhance after post-annealing. The powder X-ray diffraction analysis showed that, with the enhancement of Tc, the lattice parameters a and c increased. From thermoelectric power measurements and the evolution of the lattice constants, it is suggested that the increases in Tc may be due to the decreases in hole concentration.

Electrical properties of ferromagnetic semiconducting single-walled carbon nanotubes

Electrical properties of single-walled carbon nanotubes (SWCNTs) filled with Fe are studied by fabricating them as the channels of field-effect transistor devices. The synthesis of Fe-filled SWCNTs is realized by using ferrocene as the starting material. Our results reveal that ferrocene-filled SWCNTs show the interesting ambipolar behavior. In contrast, Fe-filled SWCNTs can exhibit high performance unipolar n-type semiconducting characteristics, suggesting the possibility of creating ferromagnetic semiconducting SWCNTs. Moreover, Coulomb blockade oscillations are significantly observed on Fe-filled SWCNTs, which indicates that they exhibit excellent single-electron transistor characteristics at low temperatures.