Spin resonance in the d-wave superconductor CeCoIn5

Abstract

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 ($\hslash \hat{I}“$=0.3 $\pm$ 0.15 meV) commensurate (${\mathbf{Q}}_0$=(1/2,1/2,1/2)) antiferromagnetic spin fluctuations and nearly isotropic spin correlations. The characteristic wavevector in CeCoIn${}_5$ is the same as CeIn${}_3$ but differs from the incommensurate wavevector measured in antiferromagnetically ordered CeRhIn${}_5$. A sharp spin resonance ($\hslash \hat{I}“<0.07$ meV) at $\hslash \ddot{I}‰$ = 0.60 $\pm$ 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 $\hat{I}”(\mathbf{q}+{\mathbf{Q}}_0)=-\hat{I}”(\mathbf{q})$.

(5 pages, 4 figures, to be published in Phys. Rev. Lett.)