Resonant Spin Excitation in an Overdoped High Temperature Superconductor

An inelastic neutron scattering study of overdoped Bi₂Sr₂CaCu₂O_8+δ ( Tc0ex0ex=0ex0ex830ex0exK) has revealed a resonant spin excitation in the superconducting state. The mode energy is Eᵣₑₛ0ex0ex=0ex0ex38.00ex0exmeV, significantly lower than in optimally doped Bi₂Sr₂CaCu₂O_8+δ ( Tc0ex0ex=0ex0ex910ex0exK, Eᵣₑₛ0ex0ex=0ex0ex42.40ex0exmeV). This observation, which indicates a constant ratio Eᵣₑₛ/kBTc~5.4, helps resolve a long-standing controversy about the origin of the resonant spin excitation in high temperature superconductors.