Spin correlations and magnetic excitation spectrum of electron-doped Nd$_{2-x}$Ce$_{x}$CuO$_{4\pm \delta }$ near the magnetic quantum critical point

One of the most intriguing issues in the field of high-T$_{c}$ superconductivity is the electron-hole asymmetry: the hole- or electron-doping of the parent Mott insulators leads to superconductors with differing properties. For the comparatively less-studied electron-doped materials, the antiferromagnetic phase extends much further with doping and appears to overlap with the superconducting phase. Our previous inelastic neutron scattering measurements show that in the compound Nd$_{2-x}$Ce$_{x}$CuO$_{4\pm \delta }$, genuine long-range antiferromagnetism does not extend as far as previously thought, and may not coexist with bulk superconductivity; the system features a magnetic quantum critical point at x$\sim $0.13, very close to the composition above which superconductivity is first observed [Motoyama \textit{et al.}, Nature \textbf{445}, 186 (2007)]. Here we present new measurements for the instantaneous spin correlations and the magnetic excitation spectrum that aim to refine our understanding of the physics in this interesting doping regime.