Ising Incommensurate Spin Resonance of CeCoIn5: A Dynamical Precursor of the Q Phase.

It is shown through detailed inelastic neutron scattering experiments that the gapped collective magnetic excitation of the unconventional superconductor CeCoIn5, the spin resonance mode, is incommensurate and that the corresponding fluctuations are of an Ising nature. The incommensurate peak position of these fluctuations corresponds to the propagation vector of the adjacent field induced static magnetic ordered phase, the so-called Q phase. Furthermore, the direction of the magnetic moment fluctuations is also the direction of the ordered magnetic moments of the Q phase. Hence, the resonance mode and the Q phase share the same symmetry and this strongly supports a scenario where the static order is realized by a condensation of the magnetic excitation.