Phase sensitive measurements of the superconducting order parameter in hole and electron doped HTS

For hole doped high-temperature superconductors (HTS) there is only little doubt left that the superconducting order parameter is of d(x2-y2) wave typ e. Several methods of phase sensitive measurements of the superconducting o rder parameter yield convincing and consistent results in case of the hole doped HTS. For the electron doped HTS there has been mounting experimental evidence for s-wave type order parameter symmetry, however, very recent mea surements are discussed as evidence for d(x2-y2)-wave symmetry. In this pap er we summarize the contradictory experimental situation with respect to th e symmetry type of the superconducting order parameter in electron doped HT S. The results from phase sensitive tunneling measurements and London penet ration depth measurements are discussed together with the new results of tr icrystal junction experiments. Additional experiments to solve this importa nt issue. as for example investigation of doping dependence and superconduc ting quantum interference experiments are suggested. (C) 2001 Elsevier Scie nce B.V. All rights reserved.