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

Abstract

For hole doped high-temperature superconductors (HTS) there is only little doubt left that the superconducting order parameter is of d x 2− y 2 wave type. Several methods of phase sensitive measurements of the superconducting order 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 measurements are discussed as evidence for d x 2− y 2 -wave symmetry. In this paper we summarize the contradictory experimental situation with respect to the symmetry type of the superconducting order parameter in electron doped HTS. The results from phase sensitive tunneling measurements and London penetration depth measurements are discussed together with the new results of tricrystal junction experiments. Additional experiments to solve this important issue, as for example investigation of doping dependence and superconducting quantum interference experiments are suggested.