Resonant spin excitation in an overdoped high temperature superconductor

An inelastic neutron scattering study of overdoped Bi2Sr2CaCu2O8+delta (T-c = 83 K) has revealed a. resonant spin excitation in the superconducting state. The mode energy is E-res = 38.0 meV, significantly lower than in optimally doped Bi2Sr2CaCu2O8+delta (T-c = 91 K, E-res = 42.4 meV. This observation. which indicates a constant ratio E-res/k(B)T(c) similar to 5.4, helps resolve a long-standing controversy about the origin of the resonant spin excitation in high temperature superconductors.