Neutron scattering study of the magnetic excitations in metallic and superconductingLa2−xSrxCuO4−y

Abstract

We report on neutron scattering studies of the dynamic spin correlations in ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{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,\ensuremath{\omega}) measured in these samples reflects to a first approximation short-range two-dimensional antiferromagnetic spin correlations closely related to those found in insulating ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$. In addition, S(Q,\ensuremath{\omega}) measured in the superconducting samples has an incommensurate, double-peaked structure which is not present in the nonsuperconducting crystal. The integrated ( F dQ) intensities of the scattering at both concentrations are nearly independent of temperature over the range ${k}_{B}$T\ensuremath{\gg}\ensuremath{\Elzxh}\ensuremath{\omega} to ${k}_{B}$T\ensuremath{\ll}\ensuremath{\Elzxh}\ensuremath{\omega} for energy transfers greater than \ensuremath{\sim}6 meV. Furthermore, the difference in the temperature dependence of the intensity between the nonsuperconducting and superconducting samples for energy transfers less than \ensuremath{\sim}6 meV suggests that a gap may be forming in the magnetic excitation spectrum of the superconducting samples. The relationship of these results to the superconductivity in ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{y}}$ is discussed.