The field distribution in the vortex lattice of a pure niobium single crystal with an external field applied along a three-fold axis has been investigated by the transverse-field muon-spin-rotation (TF-$mu$SR) technique over a wide range of temperatu
res and fields. The experimental data have been analyzed with the Delrieus solution for the form factor supplemented by phenomenological formulas for the parameters. This has enabled us to experimentally establish the temperatures and fields for the Delrieus, Ginzburg-Landaus, and Kleins regions of the vortex lattice. Using the numerical solution of the quasiclassical Eilenbergers equation the experimental results have been reasonably understood. They should apply to all clean BCS superconductors. The analytical Delrieus model supplemented by phenomenological formulas for its parameters is found to be reliable for analyzing TF-$mu$SR experimental data for a substantial part of the mixed phase. The Abrikosovs limit is contained in it.
We have investigated the dynamics of the molecular gas and the evolution of GMAs in the spiral galaxy M51 with the NRO 45-m telescope. The velocity components of the molecular gas perpendicular and parallel to the spiral arms are derived at each spir
al phase from the distribution of the line-of-sight velocity of the CO gas. In addition, the shear motion in the galactic disk is determined from the velocity vectors at each spiral phase. It is revealed that the distributions of the shear strength and of GMAs are anti-correlated. GMAs exist only in the area of the weak shear strength and further on the upstream side of the high shear strength. GMAs and most of GMCs exist in the regions where the shear critical surface density is smaller than the gravitational critical surface density, indicating that they can stably grow by self-gravity and the collisional agglomeration of small clouds without being destroyed by shear motion. These indicate that the shear motion is an important factor in evolution of GMCs and GMAs.
We theoretically investigate a non-magnetic impurity effect on the temperature dependence of the vortex core shrinkage (Kramer-Pesch effect) in a single-band s-wave superconductor. The Born limit and the unitary limit scattering are compared within t
he framework of the quasiclassical theory of superconductivity. We find that the impurity effect inside a vortex core in the unitary limit is weaker than in the Born one when a system is in the moderately clean regime, which results in a stronger core shrinkage in the unitary limit than in the Born one.
In order to consistently explain controversial experimental results on superconducting states observed by different probes in typical iron-based superconductors, we construct a realistic multi-band $pm s$-wave pairing model by combining the quasiclas
sical formalism with the first-principles calculation. The model successfully resolves the controversies in contrast to the fact that simplified models such as two-band $pm s$-wave one fail to do. A key in the model is the existence of relatively small gaps which leads to material-dependent peculiarities.
Using the time-dependent Ginzburg-Landau equation with the complex relaxation time and the Maxwell equation, we systematically examine transverse motion of vortex dynamics in the presence of pinning disorders. Consequently, in a plastic flow phase in
which moving and pinned vortices coexist, we find that the Hall voltage generally changes its sign. The origin of the sign change is ascribed to a fact that moving vortices are strongly drifted by circular current of pinned vortices and the enforced transverse moving direction becomes opposite to that by transport current. This suggests that the Hall sign change is a behavior common in all disordered type-II superconductors.
A puzzle in the iron-based superconductor LaFeAsO_{1-x}F_x is that the magnetic moment obtained by first-principle electronic structure calculations is unexpectedly much larger than the experimentally observed one. For example, the calculated value i
s ~ 2.0 mu_B in the mother compound, while it is ~ 0.3 mu_B in experiments. We find that the puzzle is solved within the framework LDA + U by expanding the U value into a slightly negative range. We show U dependence of the obtained magnetic moment in both the undoped x=0.0 and doped x = 0.125. These results reveal that the magnetic moment is drastically reduced when entering to the slightly negative range of U. Moreover, the negative U well explains other measurement data, e.g., lattice constants and electronic DOS at the Fermi level. We discuss possible origins of the negative U in these compounds.
