Vortex Dynamic Properties of Vortex-Liquid Phase in YBa2Cu3O7–δ Epitaxial Films

The current-voltage characteristics (CVC) of YBa 2 Cu 3 O 7-δ epitaxial films were determined at temperatures and magnetic fields covering the vortex-liquid region. Using functional fitting and scaling method, we derived the temperature and magnetic field dependences of the pinning potential U 0 (T,H) and critical current density J c (T,H), and current, temperature and magnetic field dependences of the effective pinning potential U eff (H, T,J) from the CVC. It is shown that the nonlinear resistance region of the vortex-liquid phase displays a process from vortex plastic motion to free flow with the dynamic exponent changing from -0.5 to 0.