Hirotaka Sano

Pressure-induced superconductivity in boron-doped Buckypapers

We show creation of paperlike thin film (Buckypaper) consisting of pseudo-two-dimensional network of boron-doped single-walled carbon nanotubes (B-SWNTs) within weakly intertube van der Waals coupling (IVDWC) state. It was formed by sufficiently dissolving as-grown ropes of B-SWNTs and densely assembling them on silicon substrate. We find that superconducting transition temperature (Tc) of 8 K under absent pressure can be induced up to 19 K by applying a small pressure to the film and that a frequency in the radial breathing phonon drastically increases with applying pressure. Discussion about IVDWC and distribution of B-SWNTs diameter imply the strong correlation.

Superconducting Transitions in Wire Network under Spatially Modulated Magnetic Field

Superconducting wire network subjected to a uniform and a checkerboard-patterned magnetic field is investigated. The checkerboard field is created by an array of ferromagnetic dots placed on top of the superconducting network. Measurements of the current–voltage ( I – V ) characteristics have revealed the canonical Kosterlitz–Thouless–Berezinskii (KTB) transition at zero magnetic field. The superconducting transition at α=1/2 (α being the frustration parameter) is studied in detail, and compared with the theoretical predictions on the fully frustrated XY model which has a double degeneracy in the ground state vortex configuration. The I – V characteristics for α=1/2 is consistent with the scenario of kink–antikink unbinding at antiphase domain boundaries first proposed by Korshunov [Phys. Rev. Lett. 88 (2002) 167007]. Introduction of the checkerboard field with amplitude β to the α=1/2 case lifts the double degeneracy. The effect of non-zero β on the nature of superconducting transition at α=1/2 is consis...

Meissner effect in films of ropes of boron-doped single-walled carbon nanotubes; Correlation with applied pressure and boron-doped multi-walled nanotubes

Superconductivity in carbon nanotubes (CNTs) is attracting considerable attention. Recently, we have reported successful boron doping into single-walled CNTs (SWNTs) and also revealed its correlation with superconductivity. In the present study, we report results of pressure-applied magnetization measurements in films consisting of ropes of boron-doped SWNTs. It reveals that Tc and magnitude for Meissner effect is mostly independent of applied pressure, while magnitude of graphite diamagnetism drastically increases as pressure increases. We also report result of resistance measurements in the samples and also correlation of boron doped SWNTs with multi-walled CNTs, in which we reported superconductivity previously.

SUPERCONDUCTING WIRE NETWORK UNDER SPATIALLY MODULATED MAGNETIC FIELD

A two-dimensional (2D) superconducting square network under spatially modulated magnetic field is studied. The super/normal phase boundaries were measured with field modulation varied. The dependence on the strength of field modulation exhibited the behavior reproducing the calculation we had done before. In addition, I-V characteristics measurements were also conducted.

Superconducting Wire Network under Spatially Modulated Magnetic Field

A two‐dimensional (2D) superconducting square network under spatially modulated magnetic field is studied. The super/normal phase boundaries were measured with field modulation varied. The dependence on the strength of field modulation exhibited the behavior reproducing the calculation we had done before. In addition, I‐V characteristics measurements were also conducted.