Comparative study of flux creep in superconductors over a broad spectrum of pinning properties

Thermal fluctuations are responsible for the phenomenon of flux creep in type-II superconductors, which allows some level of vortex motion even when the current density is below the critical current density ($J_c$). Creep studies in the high temperature oxide superconductors (HTS) have been a topic of continuous attention since the discovery of these materials. The topic is of both fundamental interest, as HTS vortex matter exhibits a rich variety of dynamic regimes, and practical relevance, as creep reduces the``effective'' $J_c$ in wires that are used for power applications. To gain a more general understanding of creep phenomena we have performed comparative studies of the time relaxation of the ``persistent'' superconducting current, $J(t)$, in a variety of type-II superconductors. The $J(t)$ was determined from magnetization (via the critical state model) using a SQUID magnetometer. The materials studied include thin films and single crystals of HTS, pnictides, MgB$_2$ and conventional low T$_c$ superconductors. This allows the spanning of several orders of magnitude in $J_c$, in the fraction $J_c$/$J_0$, where $J_0$ is the depairing current density, and in the Ginzburg number ($G_i$), which measures the importance of thermal fluctuations. I will discuss the evidence for glassy or non-glassy relaxation in the various systems.