Symmetry of the order parameter in hole and electron doped cuprate superconductors

It is well established that the order parameter symmetry in the hole doped high-temperature superconductors (HTS) is of d-wave type. In contrast, there is growing experimental evidence for a s-wave type symmetry in the electron doped cuprate superconductors. We present tunneling spectra and measurements of the London penetration depth, both supporting strongly the s-wave scenario for the electron doped HTS [1]. The absence of Andreev bound states in the tunneling spectra indicates a state without sign change of the pair potential, and the absence of low energy excitations as revealed by the London penetration depth measurements suggests a gapped state. Based on these experiments, for the materials (Nd/Pr)(1.35)Ce0.15CuO4-y an about isotropic s-wave symmetry seems more likely than a strongly anisotropic s-wave symmetry. For the Nd compound we observe anomalous low temperature behavior due to the Nd3+ magnetic moments.