Anisotropic 1/f noise and motion of magnetic vortices in YBa2Cu3O7- delta.

Abstract

Measurements of the 1/f noise have been performed on ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ single crystals for currents in the a-b plane and along the c axis. In the normal state, the normalized noise spectral density ${\mathit{S}}_{\mathit{v}}$/${\mathit{V}}^{2}$ in the a-b plane is comparable with that along the c axis. In the superconducting transition region, a large enhancement of ${\mathit{S}}_{\mathit{v}}$/${\mathit{V}}^{2}$ is observed along the c axis while no such enhancement is observed in the a-b plane. Our experimental data suggest that while the 1/f noise in the normal state may be due to structural defects, a completely different noise source exists in the superconductig transition region. We discuss the 1/f noise behavior in the superconducting transition region in terms of the anisotropic nature of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ and the motion of magnetic vortices.