Tunneling spectroscopy of superconducting ${\mathrm{Nd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4-\delta }$

The superconducting electronic states of Nd${}_{1.85}$Ce${}_{0.15}$CuO${}_{4-\delta }$ (NCCO) are studied by applying the phase-sensitive capability of tunneling spectroscopy. Unlike the YBa${}_2$Cu${}_3$O${}_{7-\delta }$ 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 $d_{x^2-y^2}$-wave and $d_{\mathrm{xy}}$-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.