Spin resonance in the d-wave superconductor CeCoIn5

Neutron scattering is used to probe antiferromagnetic spin fluctuations in the d-wave heavy fermion superconductor CeCoIn(5) (T(c)=2.3 K). Superconductivity develops from a state with slow (h Gamma=0.3 +/- 0.15 meV) commensurate [Q(0)=(1/2,1/2,1/2)] antiferromagnetic spin fluctuations and nearly isotropic spin correlations. The characteristic wave vector in CeCoIn(5) is the same as CeIn(3) but differs from the incommensurate wave vector measured in antiferromagnetically ordered CeRhIn(5). A sharp spin resonance (h Gamma < 0.07 meV) at h omega=0.60 +/- 0.03 meV develops in the superconducting state removing spectral weight from low-energy transfers. The presence of a resonance peak is indicative of strong coupling between f-electron magnetism and superconductivity and consistent with a d-wave gap order parameter satisfying Delta(q+Q(0))=-Delta(q).