In-plane penetration depth of high-temperature superconductors with single and double CuO layers

A dc technique based on the measurement of the magnetic-field dependence of the critical current of bicrystal grain boundary Josephson junctions (GBJs) is used to precisely determine the temperature change Delta lambda(ab)(T) = lambda(ab)(T) = lambda(ab)(0) of the in-plane London penetration depth of YBa2Cu3O7-delta (YBCO) and La1.85Sr0.15CuO4-delta (LSCO) thin films. The resolution of the applied measuring technique is better than 0.2 Angstrom and the measured dependences are not sensitive to extrinsic influences. Over a wide temperature range the data obtained for different high-temperature superconductors confirm with high accuracy the theoretical prediction for a d(x)2(-y)2-symmetry of the superconducting order parameter. The same temperature dependence is measured for materials with single and double CuO layers.