Non-power-law<i>I</i>–<i>V</i>characteristics in Ca-doped polycrystalline Y_1−<i>x</i>Ca_<i>x</i>Ba₂Cu₃O_7−δ

Abstract

Experiments reveal that there is a non-ohmic dissipation behaviour in the Ca-doped polycrystalline Y1−xCaxBa2Cu3O7−δ even at temperature T = 20 K. This non-ohmic dissipation seems to come from the vortex excitation along the grain boundaries and appears in anomalous I–V characteristics with a non-power-law behaviour at temperatures below 60 K, and then with a power-law behaviour as the temperature approaches Tc. This abnormal behaviour cannot be explained by the thermal flux creep model. We suppose that a giant flux motion along the grain boundaries might be responsible for this anomalous non-ohmic dissipation behaviour. A modified I–V relation was worked out based on Larkin's collective pinning model, and the analytical I–V curves were found to be coincident with the experimental curves quite well. This confirmed that the vortex excitation process along the grain boundaries in Ca-doped polycrystalline Y1−xCaxBa2Cu3O7−δ might be described with a modified collective pinning model.