MAGNETIC-RELAXATION IN HIGH-TEMPERATURE SUPERCONDUCTORS

We review experimental studies of the time decay of the nonequilibrium magnetization in high-temperature superconductors, a phenomenon known as magnetic relaxation. This effect has its origin in motion of flux lines out of their pinning sites due to thermal activation or quantum tunneling. The combination of relatively weak flux pinning and high te mperatures leads to rich properties that are unconventional in the con text of low temperature superconductivity and that have been the subje ct to intense studies. The results are assessed from a purely experime ntal perspective and discussed in the context of present phenomenologi cal theories.