Vortex motion in type II superconductors probed by muon spin rotation and SANS

We have used a variety of microscopic techniques to reveal the structure and motion of flux line arrangements, when the flux lines in low T-c type II superconductors are caused to move by a transport current. Using small-angle neutron scattering by the flux line lattice, (FLL), we are able to demonstrate directly the alignment by motion of the nearest-neighbour FLL direction. This tends to be parallel to the direction of flux line motion, as had been suspected from two-dimensional simulations. We also see the destruction of the ordered FLL by plastic flow and the bending of flux lines. Another technique that our collaboration has employed is the direct measurement of flux line motion, using the ultra-high-resolution spectroscopy of the neutron spin-echo technique to observe the energy change of neutrons diffracted by moving flux lines. The muSR technique gives the distribution of values of magnetic field within the FLL. We have recently shown that one can perform muSR measurements while the FLL is moving. Such measurements give complementary information about the local speed and orientation of the FLL motion. We conclude by discussing the possible application of this technique to thin film superconductors. (C) 2002 Elsevier Science B.V. All rights reserved.