Glassy behavior of high-T_c superconductors

This paper deals with the question of flux creep or glassy behavior in high-Tc superconducting single crystals. It is shown that the flux creep picture is merely a phenomenological approach to the glassy behavior for relatively short times and low temperatures. Glassy effects are predicted for temperatures between 70% and 95% Tc and magnetic fields in the range of 0.03 T to 0.2 T. The glass concept can be understood as a generalization of the traditional flux creep picture. A hierarchy of energy barriers dominates the physical behavior. An important technical aspect is the influence of the glassiness on critical currents.