Tunneling spectroscopy of superconducting Nd1.85Ce0.15CuO4-δ

The superconducting electronic states of Nd1.85Ce0.15CuO4-delta (NCCO) are studied by applying the phase-sensitive capability of tunneling spectroscopy. Unlike the YBa2Cu3O7-delta cases, the conductance spectra measured on (100)-, (110)- and (001)-oriented surfaces showed V-shaped gap structures, and no zero-bias conductance peaks were observed even around steps on the surfaces. The present results reject the possibility of d(x2-y2)-wave and d(xy)-wave symmetries for the pair potential in NCCO. The experimental spectra are well fitted to theoretical curves of anisotropic s-wave symmetry with a large smearing factor.