Neutron scattering study of the magnetic excitations in metallic and superconducting La2-xSrxCuO4-y

We report on neutron scattering studies of the dynamic spin correlations in La2-xSrxCuO4-y. Two superconducting and one nonsuperconducting single crystals were studied. All three of the samples exhibited metallic normal-state resistivity modified by corrections consistent with localization effects. The structure factor S(Q,) measured in these samples reflects to a first approximation short-range two-dimensional antiferromagnetic spin correlations closely related to those found in insulating La2CuO4. In addition, S(Q,) measured in the superconducting samples has an incommensurate, double-peaked structure which is not present in the nonsuperconducting crystal. The integrated (F dQ) intensities of the scattering at both concentrations are nearly independent of temperature over the range kBTLatin small letter h with stroke to kBTaLatin small letter h with stroke for energy transfers greater than 1/46 meV. Furthermore, the difference in the temperature dependence of the intensity between the nonsuperconducting and superconducting samples for energy transfers less than 1/46 meV suggests that a gap may be forming in the magnetic excitation spectrum of the superconducting samples. The relationship of these results to the superconductivity in La2-xSrxCuO4-y is discussed.