Flux-line dynamics in YBCO and BSCOO single crystals: thermal activation theory interpretation of magnetization measurements

The flux-line dynamics in YBCO and BSCCO single crystals have been studied over a wide range of frequencies (10(-3)-10(4) Hz) by means of three experimental techniques: AC susceptibility, magnetization decay and magnetization hysteresis loops. We propose an approximate schema that facilitates understanding of observed phenomenology in high-temperature superconductors (HTSC). It is based on the relationship between rho and J as deduced from thermal activation theory. We have seen that it is incorrect to apply to HTSC the approximated theories known as the thermally assisted flux flow theory and the thermally activated flux creep theory, to explain the experimental data across the whole range of frequency, temperature and magnetic field. In fact, the rho(J) relationship, reveals that an experiment on HTSC materials can involve an extended range of J values between 0 and J(c)0 and, thus, an effective pinning potential between U0 and 0, unlike the situation with low-temperature superconductors (LTSC).