Evolution of the Spin Resonance in CeCoIn5 under Magnetic Field

The evolution of the magnetic excitation spectrum of the unconventional superconductor CeCoIn 5 was studied by inelastic neutron scattering as a function of magnetic field applied in the [1,-1,0] direction. The spin resonance characteristic of the superconducting state was observed up to about H c2 /2: it is still centered at (1/2,1/2,1/2) when the magnetic field increases while its characteristic energy decreases and its lineshape substantially broadens.