s-wave symmetry along the c-axis and s+d in-plane superconductivity in bulk YBa_2Cu_4O_8

R. Khasanov, A. Shengelaya, A. Bussmann-Holder +3

To clarify the order parameter symmetry of cuprates, the magnetic penetration depth $\lambda$ was measured along the crystallographic directions $a$, $b$, and $c$ in single crystals of Y…