Anisotropy of the superconducting order parameter of Nd2-xCexCuO4 studied by STM/STS

STM/STS studies have been carried out on single crystals of the electron-doped high-T-c oxide Nd2-xCexCuO4 (x similar to 0.15:T-c similar to 20.5 K) to clarify the symmetry of its superconducting order parameter Delta. The observed gap structure of the quasi-particle excitation is found to depend on the distance between the tip and the sample surface and its characteristics indicate that the in-plane anisotropy of Delta is basically similar to that reported previously for hole-doped high-T-c oxides: It is, at first sight; xy-like but can be explained by the (x(2) - y(2)) symmetry by applying a model proposed previously [J. Phys. Sec. Jpn. 64 (1995) 1476], which takes account of the electron wave vector dependence of the tunneling probability, The zero bias conductance peak has also been observed.