Fermi-Liquid Ground State in the $n$-Type ${\mathrm{P}\mathrm{r}}_{0.91}{\mathrm{L}\mathrm{a}\mathrm{C}\mathrm{e}}_{0.09}{\mathrm{C}\mathrm{u}\mathrm{O}}_{4-y}$ Copper-Oxide Superconductor

We report nuclear magnetic resonance studies on the low-doped $n$-type copper-oxide ${\mathrm{P}\mathrm{r}}_{0.91}{\mathrm{L}\mathrm{a}\mathrm{C}\mathrm{e}}_{0.09}{\mathrm{C}\mathrm{u}\mathrm{O}}_{4-y}$ ($T_c=24\mathrm{K}$) in the superconducting state and in the normal state uncovered by the application of a strong magnetic field. We find that when the superconductivity is removed the underlying ground state is the Fermi liquid state. This result is at variance with that inferred from previous thermal conductivity measurement and appears to contrast with that in $p$-type copper oxides with a similar doping level where high-$T_c$ superconductivity sets in within the pseudogap phase. The data in the superconducting state are consistent with the line-node gap model.