## Abstract

Induced current densities j_{s} and flux relaxation of a Bi_{2}Sr_{2}CaCu_{2}O_{8} single crystal have been measured in detail as a function of temperature from T = 1.6 K up to the irreversibility temperature T_{irr} in magnetic fields up to 7 T by means of sensitive capacitance torquemeters. The dynamical relaxation rate Q ≡ d ln j_{s}/d ln(dB_{e}/dt) does not extrapolate to zero at T = 0 K, demonstrating the presence of quantum creep. The quantum creep rate Q(0) ≈ 0.03 at T = 0 is similar to values found in YBa_{2}Cu_{3}O_{7} films, although Bi_{2}Sr_{2}CaCu_{2}O_{8} is much more anisotropic than YBa_{2}Cu_{3}O_{7}. The weak field dependence of Q(0) is consistent with tunneling of 2D vortex pancakes. The induced current density j_{s}, the dynamical relaxation rate and the conventional relaxation rate R ≡ -d ln j_{s}/d ln t monitoring the time decay of j_{s} at fixed external field, are measured as a function of the field strength and its orientation with respect to the sample in detail at a fixed temperature T = 20 K. The observed non-logarithmic time dependence of j_{s} is analysed by means of a collective pinning theory. This analysis gives a good description of the observed time dependence of j_{s}, even for extremely fast relaxation processes leading to j_{s}(t)/j_{s}(0) < 0.01 in times as small as 10 s. The characteristic pinning energy U_{c}, obtained by fitting the observed time decay of j_{s} with a collective-creep model scales approximately with the c-axis component B_{e} cos Θ of the magnetic field. This scaling behaviour is also observed in the angular dependence of Q and j_{s}. For the scaling of j_{s} one has to take into account that the current is induced by only the c-axis component of the sweep rate.

Original language | English |
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Pages (from-to) | 271-283 |

Number of pages | 13 |

Journal | Physica C: Superconductivity and its applications |

Volume | 257 |

Issue number | 3-4 |

DOIs | |

Publication status | Published - 1996 Feb 1 |

Externally published | Yes |

## ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering

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