NMR study of Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$ ($x=0.17$)

Recent studies of the electron-doped high-temperature superconductor Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$ (PCCO) show very unusual physical properties at the doping level $x=0.17$. Transport experiments are consistent with the existence of a quantum critical point in the normal state. Within the superconducting state, specific heat measurements in a magnetic field are interpreted as evidence for a transition in superconducting order parameter symmetry. We report the $^ {63,65} $Cu-NMR spectrum and spin dynamics of PCCO single crystals with $x=0.17$ and contrast their properties with crystals of $x=0.15 $. The anisotropic Knight shifts are dominated by the Pr$^{3+}$ moments and change little between the samples. The spin lattice relaxation rates are affected by the doping, as are the linewidths at low temperatures. \\ $^\ast$This work is supported at UCLA by NSF Grants DMR-0334869 (WGC) and 0203806 (SEB).