s -Wave Symmetry Along the c -Axis and s + d In-plane Superconductivity in Bulk YBa2Cu4O8
Khasanov, R. ; Shengelaya, A. ; Karpinski, J. ; Bussmann-Holder, A. ; Keller, H. ; Müller, K.
In: Journal of Superconductivity and Novel Magnetism, 2008, vol. 21, no. 2, p. 81-85
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- To clarify the order parameter symmetry of cuprates, the magnetic penetration depth λ was measured along the crystallographic directions a, b, and c in single crystals of YBa2Cu4O8 via muon spin rotation. This method is direct, bulk sensitive, and unambiguous. The temperature dependences of λ a −2 and λ b −2 exhibit an inflection point at low temperatures as is typical for two-gap superconductivity (TGS) with s+d-wave character in the planes. Perpendicular to the planes a pure s-wave gap is observed thereby highlighting the important role of c-axis effects. We conclude that these are generic and universal features in the bulk of cuprates