Anisotropy of the Superconducting Order Parameter of Nd_{<b>2</b>-<i><i>x</i></i>}Ce_{<i><i>x</i></i>}CuO_<b>4</b>Studied by STM/STS

Abstract

STM/STS studies have been carried out on single crystals of the electron-doped high- T c oxide Nd 2- x Ce x CuO 4 ( x ∼0.15, T c ∼20.5 K) to clarify the symmetry of its superconducting order parameter Δ. 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 Δ is basically similar to that reported previously for hole-doped high- T c oxides: It is, at first sight, x y -like but can be explained by the ( x 2 - y 2 ) symmetry by applying a model proposed previously [J. Phys. Soc. 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.