Spin Dynamics in the electron-doped high-$T_c$ superconductors Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-\delta}$

We briefly review results of recent neutron scattering experiments designed to probe the evolution of antiferromagnetic (AF) order and spin dynamics in the electron- doped Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-\delta}$ (PLCCO) as the system is tuned from its as-grown non-superconducting AF state into an optimally doped superconductor ($T_c$ = 27.5 K) without static AF order [1-3]. For under doped materials, a quasi-two- dimensional spin-density wave was found to coexist with three- dimensional AF order and superconductivity. In addition, the low-energy spin excitations follow Bose statistics. In the case of optimally doped material, we have discovered a magnetic resonance intimately related to superconductivity analogous to the resonance in hole-doped materials. On the other hand, the low energy spin excitations have very weak temperature dependence and do not follow Bose statistics, in sharp contrast to the as-grown nonsuperconducting materials. 1 Stephen D. Wilson, Pengcheng Dai, Shiliang Li, Songxue Chi, H. J. Kang, and J. W. Lynn, Nature (London) {\bf 442}, 59 (2006). 2 Stephen D. Wilson, Shiliang Li, Hyungje Woo, Pengcheng Dai, H. A. Mook, C. D. Frost, S. Komiya, and Y. Ando, Phys. Rev. Lett. {\bf 96}, 157001 (2006). 3. Stephen D. Wilson, Shiliang Li, Pengcheng Dai, Wei Bao, J. H. Chung, H. J. Kang, S.-H. Lee, S. Komiya, and Y. Ando, Phys. Rev. B {\bf 74}, 144514 (2006).