QUANTUM MAGNETIC EXCITATION IN HIGH-T_c SUPERCONDUCTORS AND THE RELATED MATERIALS. Masatoshi Arai, National Laboratory for High Energy Physics, 1-1 Oho, Tsukuba 305, Japan

Recent development of the pulsed neutron scattering technique has given very good opportunities to observe spin dynamics of low dimensional magnetic system. The magnetic dynamic structure factor in the wide range of the energy-momentum space can be observed in one time. Those were demonstrated on KFeS₂ [1], KCuF₃ [2], CsVCl₃ [3]. In this paper I will present on the quantum spin dynamics of the spin-Peierls system CuGeO₃ (T_sp=14K) and the high-Tc superconductor. La_1.85Sr_0.15CuO₄ (T_c=37K). For CuGeO₃ the double spin on continuum with J-10meV was clearly observed, which is surrounded by the lower boundary of the des Cloizeaux and Pearson type and the upper boundary with twice the energy and periodicity. Below T_sp a sharp excitation appeared at the zone boundary due to the halving of the Brillouin zone. The continuous magnetic excitation of La_1.85Sr_0.15CuO₄ has also observed, which extends up to 280meV. Raising temperature does not affect the dynamic property at the high energy region but at the lower energy feature around the famous incommensurate peaks. In the paper I will discuss the similarity/difference to/between the quantum excitation of the localized spin singlet pairs in the spin-Peierls state and of the itinerant RVB singlet pairs in the super conducting state.

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