Vortex phases and glassy dynamics in the highly anisotropic superconductor HgBa(2)CuO(4+δ)

We present an extensive study of vortex dynamics in a high-quality single crystal of HgBa(2)CuO(4+δ), a highly anisotropic superconductor that is a model system for studying the effects of anisotropy. From magnetization M measurements over a wide range of temperatures T and fields H, we construct a detailed vortex phase diagram. We find that the temperature-dependent vortex penetration field H(p)(T), second magnetization peak H(smp)(T), and irreversibility field H(irr)(T) all decay exponentially at low temperatures and exhibit an abrupt change in behavior at high temperatures T/T(c) >~ 0.5. By measuring the rates of thermally activated vortex motion (creep) S(T, H) = |dlnM(T, H)/dlnt|, we reveal glassy behavior involving collective creep of bundles of 2D pancake vortices as well as temperature- and time-tuned crossovers from elastic (collective) dynamics to plastic flow. Based on the creep results, we show that the second magnetization peak coincides with the elastic-to-plastic crossover at low T, yet the mechanism changes at higher temperatures.