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[en] The local vibration spectra of hydrogen atoms dissolved in tantalum have been studied by the energy-loss scattering of pulsed neutrons. The observed time-of-flight spectra show split peaks of the local modes near 120 and 175 meV, which are almost invariant with changing concentration (H/Ta=0.1, 0.5 and 0.7) and configuration of hydrogen at 200 and 850C. From comparison with previous neutron results on niobium and vanadium hydrides, it is shown that the energies of the split local modes are nearly independent of the metal-hydrogen distance, and the relative intensity and the FWHM of the high energy mode increase in the disordered phase at 850C in comparison with the ordered phase at 200C. (auth.)
[en] The doping-evolution of spin and charge dynamics in a doped Mott insulator is an important issue in the research field of strongly correlated electron system. The entire excitation spectra have been intensively and continuously studied with the development of spectroscopic techniques after the discovery of high-transition-temperature (high-TC) superconductivity in a lamellar cuprate oxide. The recent state-of-the-art spectrometers at large research facilities such as J-PARC enables us to study the details of composite dynamics in the energy-momentum space arising from the interacting degrees of freedom. Although the comprehensive study on both hole- and electron-doped systems are indispensable to extract the universal mechanism of high-TC superconductivity, the majority of spectroscopic measurements was done on the hole-doped system. The systematic research on the electrondoped system has been lucking, mainly due to the difficulties in the crystal growth and the emergence of superconductivity through the heat treatment. Here, we introduce the results of inelastic Neutron Scatteringmeasurements on the spin excitation in the electron-doped copper oxide, which was obtained after overcoming the above experimental difficulties. First, we confirmed that the spin excitation in Pr1.4La0.6CuO4, which is the parent compound of electron-doped superconductor, is consistent with the spin-wave excitation expected from the s=1/2 two-dimensional Heisenberg model. The evaluated nearest neighbor exchange coupling is 140±5 meV, consistent with the value for the parent compound of hole-doped superconductor, La2CuO4. Furthermore, the evidence of higher term of exchange coupling was confirmed from the detailed momentum-dependence of high-energy dispersion in the CuO2 plane. It was newly found that the spin excitation tends to elongate toward the higher energy region upon electrondoping in Pr1.4-xLa0.6CexCuO4 and the zone boundary energy exceeds 300 meV in the sample with x ≥ 0.08, suggesting the steeper dispersion in the highly doped samples. This dopingevolution is in stark contrast with a negligible doping effect on the high-energy spin excitation in the hole-doped La2-xSrxCuO4, Therefore, the electron-hole asymmetry exists in the observed spin excitation against the doping.