Neutron Scattering Studies On Magnetism And Phonon In The Electron Doped Nd2subscript Xcesubscript Xcuo4 And Pr1subscript Xlacesubscript Xcuo4 PDF Download

We present comprehensive neutron scattering studies on the electron-doped superconductors Nd2[subscript x]Ce[subscript x]CuO4 and Pr1[subscript x]LaCe[subscript x]CuO4 to understand how magnetic properties and phonon are related to superconductivity. For superconducting Nd1[subscript point]5Ce0[subscript point]15CuO4, a[italicized c]-axis magnetic field enhances the commensurate antiferromagnetic order, while an [italicized ab]-plane magnetic field induces spin-flop transition from a noncollinear to a collinear magnetic structure. The [italicized c]-axis field-induced effect is absent in both parent Nd2CuO4 and the as-grown nonsuperconducting Nd1[subscript point]5Ce0[subscript point]15CuO4 samples. These results, combined with those on the hole-doped La2−[subscript x]Sr[subscript x]CuO4 suggest that the antiferromagnetism competes with supercondictivity. In the Pr1−[subscript x]LaCe[subscript x]CuO4 system, we find that quasi-2 dimensional commensurate antiferromagnetism coexists with superconductivity and 3 dimensional antiferromagnetism. To determine whether the antiferromagnetic order is the competing order in the high temperature superconductors, regardless of hole-doping or electron-doping, we performed field-induced experiments on the electron-doped superconductor Pr0[subscript point]88LaCe0[subscript point]12CuO4[subscript plus or minus delta] by applying magnetic fields along the [italicized c]-direction and in the [italicized ab]-plane direction. The anisotropy of the field-induced moment demonstrates the competing nature of these two order parameters. We find that the spin-flop transition induced by an [italicized ab]-plane magnetic field in the lightly electron-doped Pr1[subscript point]29La0[subscript point]--Ce0[subscript point]01CuO4 affects significantly both in-plane and out-of-plane resistivity. No magnetoresistance anomaly is observed when a [italicized c]-axis magnetic field is applied, consistent with the absence of a spin-flop transition for such field direction. This anisotropic magnetoresistance effect suggests that there is spin-charge coupling in the electron-doped superconductors as well as in the hole-doped ones. Inelastic neutron scattering has been performed to study the generalized phonon density of states (GDOS) of electron-doped Nd2−[subscript x]Ce[subscript x]CuO4 with various levels of doping. Upon doping, the softening of phonon around 70 me V 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. Therefore, the electron-lattice coupling in the electron-doped Nd2−[subscript x]Ce[subscript x]CuO4 is different from that in the hole-doped materials.