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 becaus e both systems have the copper oxygen planes in common. However, our experi ments based on bicrystal grain boundary junctions (GBJs) show the absence o f zero energy Andreev bound states as well as a s-wave like temperature dep endence of the London penetration depth thereby excluding a d-wave symmetry of the order parameter in the electron-doped cuprates. At present, it is n ot fully established whether the electron-doped HTS have an isotropic or an anisotropic s-wave symmetry of the order parameter. (C) 2000 Elsevier Scie nce B.V. All rights reserved.