Determination of the order parameter symmetry 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. For the electron-doped HTS one could expect to find the same order parameter symmetry because both systems have the copper oxygen planes in common. However, our experiments based on bicrystal grain boundary junctions (GBJs) show the absence of zero energy Andreev bound states as well as a s-wave like temperature dependence of the London penetration depth thereby excluding a d-wave symmetry of the order parameter in the electron-doped cuprates. At present, it is not fully established whether the electron-doped HTS have an isotropic or an anisotropic s-wave symmetry of the order parameter.