Anisotropic irreversibility of the Abrikosov and Josephson flux dynamics in YBa2−xSrxCu3O7−δ single crystals: Bose-glass and vortex-glass features

Abstract

Very detailed magnetic irreversibility data for fields applied along the c axis or the ab plane of a pure and untwinned YBa2Cu3O7−δ single crystal and Sr-doped and heavily twinned YBa2−xSrxCu3O7−δ (x=0.25, 0.37, and 0.5) single crystals are reported. The irreversibility lines Tirr(H) of the pure single crystal show a considerable planar anisotropy but follow the same power-law regime, for both field orientations, arising within the conventional flux-creep theories in the whole field range. Very differently, however, the Tirr(H) lines of the doped superconductors exhibit besides large anisotropies, several different regimes. In fields lower than 8 kOe the Tirr(H) data of the doped samples display the de Almeida–Thouless (AT) and Gabay-Toulouse (GT)-like power-law behaviors, the signature of a frustrated superconductor. For higher-field values, and in particular for H‖c, flux dynamics seems to be conventional. However, for H‖ab and field values above 30 kOe, the flux dynamics displays sharp directional properties along the twinning planes (TP’s) for rotations about the c axis. This behavior is cusplike, comparable to that caused by columnar defects, which characterizes a Bose-flux-glass phase. We appoint the superconducting granularity and frustration as responsible for the AT and GT behaviors below 8 kOe and the strong anisotropic pinning for H parallel to the TP’s as the cause of the Bose-glass features. On the other hand, the isotropic pinning for large angular displacements or for any angle in fields below 30 kOe is the most probable cause of the vortex-glass features.

Source-reported materials — not catalogue approval

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