Neutron Scattering Studies on Magnetism and Phonon in the Electron-doped Nd2-xCexCuO4 and Pr1-xLaCexCuO4

We present comprehensive neutron scattering studies on the electron-doped superconductors Nd_2-xCe_xCuO₄ and Pr_1-xLaCe_xCuO₄ to understand how magnetic properties and phonon are related to superconductivity. For the superconducting Nd_1.85Ce_0.15CuO₄, a c-axis magnetic field enhances the commensurate antiferromagnetic order, while an ab-plane magnetic field induces spin-flop transition from the noncollinear to the collinear magnetic structure. The c-axis field-induced effect is absent in both the parent Nd₂CuO₄ and the as-grown nonsuperconducting Nd_1.85Ce_0.15CuO₄ samples. These results, combined with those on the hole-doped La_2-xSr_xCuO₄ suggest that antiferromagnetism competes with superconductivity.

In the Pr_1-xLaCe_xCuO₄ system, we find that quasi-2 dimensional commensurate antiferromagnetism coexists with superconductivity and 3 dimensional antiferromagnetism in the underdoped region. To determine whether the antiferromagnetic order is the competing order in high temperature superconductors, regardless of hole-doping or electron-doping, we performed field-induced experiments on the electron-doped superconductor Pr_0.88LaCe_0.12CuO_4±δ by applying magnetic fields along the c-direction and in the ab-plane direction. The anisotropy of the field-induced moment demonstrates the competing nature of these two order parameters.

Inelastic neutron scattering has been performed to study the generalized phonon density of states (GDOS) of electron-doped Nd_2-xCe_xCuO₄ with various levels of doping. Upon doping, the softening of phonon around 70 meV has been observed. However, most of the softening occurs within a few percent of Ce doping, and it is not related to the doping induced nonsuperconducting-superconducting transition.