NMR studies of Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$ ($\it{x}$ = 0.15 and 0.17) at high magnetic field

Recent charge and thermal transport measurements on the electron- doped high-T$_{c}$ superconductor Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$ (PCCO) show unusual behavior in the superconducting dome at the doping level going from $\it{x}$ = 0.15 (optimally doped) to 0.17 (overdoped), such as quantum phase transition and electron paring symmetry changes, suggesting a possible connection between the superconductivity and other competing phases like antiferromagnetism. We report the $^{63,65}$Cu-NMR spectrum in PCCO single crystals with $\it{x}$ = 0.17 in a high magnetic field B$_{0}$, and contrast their properties with those of $\it {x}$ = 0.15. The temperature dependence of the $^{63,65}$Cu-NMR Knight shift is dominated by the negative isotropic hyperfine coupling to the field-induced Pr$^{3+}$ ion moment, and changes little between $\it{x}$ = 0.15 and 0.17. The $^{63,65}$Cu-NMR linewidths are propotional to the applied magnetic field B$_{0} $, but affected by the doping, indicating the existence of other sources besides the Pr$^{3+}$ ion moment that contributes to the static local field distribution at the Cu nuclei. The work at UCLA is supported at UCLA by NSF Grants DMR-0334869 (WGC) and 0203806 (SEB).