Fluxoids and neutron polarisation effects

There are several ways of investigating flux lines with polarised neutrons. We shall describe our recent work on IN 15 at ILL, investigating spatially varying fields perpendicular to the fluxoid axes, which are present with t ilted fields in anisotropic superconductors. These field components may be detected by polarisation analysis of neutrons diffracted by the flux line l attice, and allow a detailed investigation of flux structure in such materi als as YBCO and NbSe2. A further application of polarised neutrons is the u se of neutron spin-echo techniques to measure the speed of moving flux line s. We have recently demonstrated this in an Nb-Ta alloy on instruments IN11 and IN15, by measuring the energy change of neutrons diffracted by flux li nes, which are moving under the influence of a transport current. We shall also comment on others' work on the search for interference terms between f lux lattice and nuclear diffraction signals, and the use of neutron depolar isation for investigation of flux distributions in superconductors. (C) 199 9 Elsevier Science B.V. All rights reserved.