T. Masui

We report electronic Raman scattering measurements on out-of-plane disordered Bi _{2+ x} Sr _{2- x} CaCu ₂ O _8+δ . With increasing out-of-plane disorder, the critical temperature T _c is significantly suppressed, but suppression of the superconducting gap energy is observed only in the nodal region. Our experimental finding advocate the two-gap scenario that the origins of the nodal and the antinodal gap are different.

In thin films of anisotropic superconductors, the intervortex interaction may be strongly modified because of the interplay between the long-ranged repulsion caused by an extremely slow decay of the supercurrent induced by a single vortex line (Pearl’s effect) and the attraction caused by the tilt of the vortex lines with respect to the anisotropy axes. We present a theoretical analysis and Lorentz microscopy experimental data for high-temperature superconducting cuprates which provide evidence of such interplay. Moreover we report on a theoretical prediction of a very special type of the vortex arrangement—the formation of the vortex molecules.

The electronic properties of the carbon substituted MgB$_2$ single crystals are reported. The carbon substitution drops T$_c$ below 2 K. In-plane resistivity shows a remarkable increase in residual resistivity by C-substitution, while the change of in-plane/out-of-plane Hall coefficients is rather small. Raman scattering spectra indicate that the E$_{2g}$-phonon frequency radically hardens with increasing the carbon-content, suggesting the weakening of electron-phonon coupling. Another striking C-effect is the increases of the second critical fields in both in-plane and out-of-plane directions, accompanied by a reduction in the anisotropy ratio. The possible changes in the electronic state and the origin of T$_c$-suppression by C-substitution are discussed.