Abstract
We have performed a detailed anisotropy study of the superconducting properties of untwinned single crystals of for δ≊0.1 and δ≊0.4 in magnetic fields up to 22 T using a rf method giving critical fields which are determined by the onset of flux-line motion. For δ≊0.1 we find the highest along the b axis; the a-b anisotropy amounts to 20% at 85 K. The 60-K superconductivity for δ≊0.4 is characterized by the largest along the a axis and pronounced 2D behavior as manifested by a cusp in the angular dependence of and by the extremely steep slope of (T) perpendicular to c. We discuss our experimental results with respect to the significance of the Cu-O chains for the high- superconductivity of .
- Received 11 July 1989
DOI:https://doi.org/10.1103/PhysRevLett.63.2520
©1989 American Physical Society