Neutron scattering study of spin fluctuations in La_2-xSr_xCuO₄ by four-dimensional mapping of neutron cross-sections using the 4SEASONS chopper spectrometer

Spin fluctuation spectra and phonon neutron cross-sections of La₂CuO₄ and La_2-xSr_xCuO₄ with x = 0.075 and 0.30 were studied by four-dimensional mapping of neutron cross-sections using the 4SEASONS chopper spectrometer installed at the Material and Life Science Facility, J-PARC. The purpose of this study is to verify the relation between the maximum at the energy transfer of 15 meV in dynamical spin susceptibility and the superconductivity. We observed identical maxima in spin fluctuation spectra at 15 meV at several L positions in the data of the superconducting x = 0.075 sample measured at 5 K. In addition, we confirmed that the maximum disappears in the 200 K data of the x = 0.075 composition and in the 5 K data of the undoped La₂CuO₄. These results imply that the 15 meV maximum is a unique feature of the superconducting concentrations at low temperatures. (author)