J. Phys. I France
Volume 3, Numéro 3, March 1993
Page(s) 863 - 870
DOI: 10.1051/jp1:1993168
J. Phys. I France 3 (1993) 863-870

Field and temperature dependence of the mean penetration rate of fluxons in the mixed state of high- $T_{\rm c}$ superconductors

Mitsuru Uehara1 and Bernard Barbara2

1  National Research Institute For Metals, 1-2-1, Sengen Tsukuba, Ibaraki-305, Japan
2  Laboratoire Louis Néel, CNRS, 166X, 38042 Grenoble Cedex, France

(Received 12 November 1991, revised 9 October 1992, accepted 15 October 1992)

The time decay of the zero field cooled diamagnetic magnetization of superconducting Bi(Pb) 2Sr 2Ca 2Cu 3O $_{\rm y}$ and YBa 2Cu 3O $_{7-\delta}$ ceramics has been measured and analyzed in terms of a mean activation energy $\bar{E}$. We find $\bar{E} \propto H_{\rm c}(T)[H^{-1}-H^{-1}_0]$ where $H_{\rm c}(T)$ is the thermodynamic critical field, H the applied one and H0 a constant. The proportionality coefficient as well as the characteristic field H0, depend sensitively on the level of diamagnetic susceptibility $P_f = - 4 \pi M_f H$ at which experiments are performed. Our experiments show below 10 K the existence of an anomaly on the mean activation energy. Different possible alternatives to explain this phenomenon are considered, the most probable being a (thermally assisted) quantum tunneling of vortex lines.

74.30C - 74.60J - 74.60G

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