Inhaltszusammenfassung

We have investigated the thermally activated behavior of the in-plane electrical resistivity of Bi2Sr2CaCu2O8+δ films for magnetic fields B<~104G applied parallel to the c axis. The activation energy in the vortex-liquid state changes suddenly at a crossover field Bcr. The anisotropy reduction generated by oxygen annealing leads to the increase of the crossover field. For B<Bcr, the activation energy U is weakly magnetic-field dependent. For B>Bcr, U(B,T)∼(1-T/Tc0)/B1/2, which corresponds to ...We have investigated the thermally activated behavior of the in-plane electrical resistivity of Bi2Sr2CaCu2O8+δ films for magnetic fields B<~104G applied parallel to the c axis. The activation energy in the vortex-liquid state changes suddenly at a crossover field Bcr. The anisotropy reduction generated by oxygen annealing leads to the increase of the crossover field. For B<Bcr, the activation energy U is weakly magnetic-field dependent. For B>Bcr, U(B,T)∼(1-T/Tc0)/B1/2, which corresponds to an entangled vortex fluid. The observation of vortex-liquid entanglement in the presence of relevant quenched disorder is discussed in connection with the relation between the theoretically predicted entanglement length for a clean system and the collective pinning length along the field direction. Our results suggests that, in the case of a pronounced anisotropy and significant collective pinning, the entanglement field BE=Bcr≈Φ0/γ2s2, where s is the interlayer spacing. » weiterlesen» einklappen

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Klassifikation

DFG Fachgebiet:
Physik der kondensierten Materie

DDC Sachgruppe:
Physik