Temperature dependence of the magnetic penetration depth in the high-Tc superconductor Ba2YCu3O9-δ: Evidence for conventional s-wave pairing

Transverse-field muon-spin-relaxation (μSR) measurements have been performed on Ba2YCu3O9-δ (δ=2.1±0.05) above and below its superconducting transition temperature. The temperature dependence of the magnetic penetration depth, deduced from the μSR data, is that of an ordinary s-wave (not d-wave with nodes in the gap function) superconductor. The data at 6 K indicate a magnetic penetration depth of λ≈1400 Å which, in the limit of extreme anisotropy, reduces to λ≈1065 Å.