Unambiguous evidence for nearly isotropic s-wave gap in the bulk of optimally electron-doped Nd_{1.85}Ce_{0.15}CuO$_{4-y}

Abstract

We address an important issue as to whether bulk-sensitive data of Raman scattering, optical conductivity, magnetic penetration depth, directional point-contact tunneling spectra, and nonmagnetic pair-breaking effect in optimally electron-doped Nd_{1.85}Ce_{0.15}CuO_{4-y} support a nodeless s-wave or d-wave superconducting gap. We numerically calculate Raman intensities, directional point-contact tunneling spectra, and nonmagnetic pair-breaking effect in terms of both s-wave and d-wave gap symmetries. We find that all these bulk-sensitive data are in quantitative agreement with a nearly isotropic s-wave gap. The fact that T_{c} is nearly independent of the residual resistivity rules out any d-wave gap symmetry.