Fluctuation conductivity along the c-axis and parallel to the ab-planes in melt-textured YBa2Cu3O7−δ samples doped with Y211 phase

We report measurements of in-plane and out-of-plane fluctuation conductivity under low applied magnetic fields up to 500 Oe in two melt-textured YBa₂Cu₃O_7−δ (YBCO) samples. 3D-Gaussian and genuine critical 3D-XY-E fluctuation regimes were identified in the conductivity parallel to the ab plane. In addition, a regime beyond 3D-XY was observed in the immediate vicinity of the superconducting transition of the in-plane fluctuation conductivity. The 3D-XY-E scaling was also identified in the fluctuation conductivity along the c-axis in the sample with smaller content of the Y₂BaCuO₅ (Y211) phase. This result indicates that the superconducting state in YBCO has a three-dimensional character, in contradiction to some studies suggesting that critical phenomenology is fundamentally distinct in orientations parallel or perpendicular to the Cu-O₂ planes of the high-temperature superconductors. However, the results suggests the presence of a sub-dominant order-parameter component in YBCO that has an appreciable projection along the c-axis.