To study the detailed structure of the magnetic excitation spectrum, we performed a neutron scattering experiment on optimally electron-doped Pr 0.89LaCe0.11CuO4 (Tc = 25:5 K). Well-defined spin excitations existed up to an energy of ω ∼ 180 meV, which is consistent with the recent observation by Wilson et al. [Phys. Rev. Lett. 96 (2006) 157001] for the same cuprate with a different Tc. Better statistics in our experiment revealed a more precise structure of the spectrum. As the energy increased up to ωc ∼ 60 meV, the peak width (κ) markably increased, but in the high-energy region beyond ωc the width remained nearly independent of the energy. χ″(ω) showed a sharp peak at ω = 6 meV, which markably diminished as the energy increased until eventually a well-defined magnetic signal was not observed near ωc. However, a broad magnetic peak at (π, π) reappeared beyond ω ∼ 100 meV. We discuss the nature of the spin excitation spectrum, which is vastly different from that of a conventional spin wave excitation with localized spins.
- Electron-doped superconductor
- Inelastic neutron-scattering measurement
- Spin excitations