Superconducting anisotropy in double-chain YBa2Cu4O8 single crystals

The c-axis anisotropy parameters of an YBa2Cu4O8 single crystal are gamma (ca) = (m(c)/m(a))(1/2) = 13.4 +/- 0.32 and gamma (cb) = (m(c)/m(a))(1/2) = 14.7 +/- 0.39 at 70 K in 10 kG. The in-plane anisotropy gamma (ab) = 1.12 +/- 0.06 is much smaller than gamma (ab) = 3 estimated from the normal-state resistivity, and is even smaller than y.b = 1. 18 0.05 of YBa, C11307, We consider that the CuO double chains do not exhibit their own superconductivity but presumably the proximity-induced superconductivity. The peak effects appeared in the torque curves suggest that the vortex phase diagram of YBa2Cu4O8 has an internal structure. (C) 2001 Elsevier Science B.V. All rights reserved.