Persistence of High-Frequency Spin Fluctuations in Overdoped SuperconductingLa2−xSrxCuO4(x=0.22)

Abstract

We report a detailed inelastic neutron scattering study of the collective magnetic excitations of overdoped superconducting ${\mathrm{La}}_{1.78}{\mathrm{Sr}}_{0.22}{\mathrm{CuO}}_4$ for the energy range 0–160 meV. Our measurements show that overdoping suppresses the strong response present for optimally doped ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ which is peaked near 50 meV. The remaining response is peaked at incommensurate wave vectors for all energies investigated. We observe a strong high-frequency magnetic response for $E\gtrsim 80\mathrm{meV}$ suggesting that significant antiferromagnetic exchange couplings persist well into the overdoped part of the cuprate phase diagram.