MOTIONS OF THE FLUX LINES IN HIGH-T-C SUPERCONDUCTORS FROM NMR LINEWIDTH, RELAXATION AND SPIN-ECHO DECAY

The motion of the flux lines (FL) in high temperature superconductors and their relationship with the NMR quantities are reviewed and discus sed in the light of recent Y-89 NMR experiments in YBCO-type compounds . Tn particular measurements involving the Y-89 Spin echo attenuation induced both by the thermal excitation of the FL's and by motions driv en by DC current and pulsed magnetic fields are presented, with prelim inary results and lines of interpretation. Flux line motion as observe d with Hg-199 NMR in HgBa2CuO4+delta high temperature superconductor i s discussed.