MAGNETIC-FIELD VARIANCE IN LAYERED SUPERCONDUCTORS

In highly anisotropic or layered high-T(c) superconductors with magnetic field along the c axis, both pinning-caused and thermal fluctuations of the highly flexible vortex cores, or of chains of vortex dots, threading the superconducting layers may drastically reduce the variance-sigma of the magnetic-field fluctuation. In contrast, the fluctuations of the averaged flux lines (smoothed over the in-plane penetration depth-lambda) increase-sigma. As a consequence, muon-spin-rotation lines may be sharpened not only by thermal motional narrowing, but also by pinning-caused static disorder.