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The importance of type-II superconductors with strong pinning comes from their ability to carry large transport currents in the presence of a magnetic field. We report on the results of the bulk magnetization measurements in the superconducting state in clean single crystals of NdFeAsO 0.9 F 0.1 at various temperatures. The zero-temperature superconducting critical current density, J c , where the superconducting transition temperature T c reaches a maximum of 45(1) kelvin, displays a remarkable high value. The field dependence of the critical current density was analyzed within the collective pinning model. A remarkably good agreement between the experimental results and theoretical δ1 pinning curve is obtained. This indicates that pinning in NdFeAsO 0.9 F 0.1 crystal originates from spatial variation of the mean free path. Additionally, the normalized pinning force density, F p , curves verses H/H irr (H irr is the irreversibility field) were scaled using the Dew-Hughes model. Our analysis suggests that point pinning alone cannot explain the observed field variation of F p . [ABSTRACT FROM AUTHOR]

Using the nonlinear Ginzburg–Landau equations we study the vortex configurations in a superconducting square with a central square pillar in the presence of a uniform applied magnetic field. The presence of the pillar changes the vortex structure in the superconducting sample considerably. We calculate magnetization, magnetic induction, supercurrent and vorticity, which show different vortex configurations as a function of magnetic field. [ABSTRACT FROM AUTHOR]

In order to study site-selective NMR in chiral p -wave superconductors, we calculate local nuclear relaxation rate T 1 − 1 in the vortex lattice state by Eilenberger theory with and without non-magnetic impurity scattering in the Born limit and unitary limit. The local T 1 − 1 in the NMR resonance line shape is different between two chiral states p ± , depending on whether the chirality is parallel or anti-parallel to the vorticity. In the p − -wave, anomalous suppression of local T 1 − 1 occurs around the vortex core due to the negative coherence term coming from odd-frequency s -wave Cooper pair induced around the vortex. We especially examine the site dependence of the anomalous suppression of local T 1 − 1 , including the applied magnetic field dependence and the impurity effects. [ABSTRACT FROM AUTHOR]