Influence of the a.c. and d.c. electrical current density on the normal-superconductor transition in high-temperature superconductors☆

Abstract Detailed a.c. and d.c. measurements of the electrical resistivity, ρ, of Ba 2 Ln 1 Cu 3 O 7 − δ (Ln ≡ Y, Ho) polycrystalline samples, using a current density, J , spanning the range 4 × 10 −3 A cm −2 ⩽ J ⩽ 2 A cm −2 are reported. In particular, the resistivity behaviour near and above the superconducting critical temperature T c is shown to have no dependence on the current density. This finding gives further support to the theory that fluctuations are responsible for the resistivity rounding above T c and suggests that no percolative process is involved.