Novel Spin Excitations in Optimally Electron-Doped Pr_<0.89> LaCe_<0.11> CuO_4(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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To study the detailed structure of the magnetic excitation spectrum, we performed a neutron scattering experiment on optimally electron-doped Pr_<0.89>LaCe_<0.11>CuO4 (T_c=25.5K). Well-defined spin excitations existed up to an energy of ω〜180meV, which is consistent with the recent observation by Wilson et al. [Phys. Rev. Lett. 96 (2006) 157001] for the same cuprate with a different T_c. Better statistics in our experiment revealed a more precise structure of the spectrum. As the energy increased up to ω_c〜60meV, the peak width (κ) markably increased, but in the high-energy region beyond ω_c the width remained nearly independent of the energy. χ" (ω) showed a sharp peak at ω=6meV, which markably diminished as the energy increased until eventually a well-defined magnetic signal was not observed near ω_c. However, a broad magnetic peak at (π, π) reappeared beyond ω〜100meV. We discuss the nature of the spin excitation spectrum, which is vastly different from that of a conventional spin wave excitation with localized spins.
社団法人日本物理学会の論文
2006-09-15