Phonon density of states inR2CuO4and superconductingR1.85Ce0.15CuO4(R=Nd,Pr)

Inelastic-neutron-scattering measurements of the generalized phonon density of states (GDOS) for the electron-doped superconductors ${\mathrm{Nd}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_4$ and ${\mathrm{Pr}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_4$ have been carried out with the use of both a filter-detector method and time-of-flight spectroscopy. A measurement of the GDOS for the insulating ${\mathrm{Pr}}_2$ ${\mathrm{CuO}}_4$ was also done for comparison with that of ${\mathrm{Pr}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_4$, while a more limited set of data was obtained for ${\mathrm{Nd}}_2$ ${\mathrm{CuO}}_4$. Comparison between the GDOS spectrum of the ${\mathrm{Nd}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_4$ with that of ${\mathrm{Pr}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_4$ shows differences in the shape of some structures in the GDOS spectrum. Furthermore, there are substantial changes in the GDOS spectrum of ${\mathrm{Pr}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_4$ as compared to that of ${\mathrm{Pr}}_2$ ${\mathrm{CuO}}_4$, particularly in the energy regime between 33 and 63 meV.