Evolution of the Spin Resonance of CeCoIn5 as a Function of Magnetic Field and La Substitution

We report the evolution of the spin resonance in CeCoIn 5 as a function of magnetic field and lanthanum substitution. In both cases, the resonance peak position shifts to lower energy and the lineshape broadens. For La doping, it is found that the ratio Ω res / k B T c is almost constant as a function of x . Under magnetic field the decrease of the excitation energy is similar for H ∥[1 1 0] and [111] and faster than the decrease of T c ( H ). The Zeeman effect found for the field applied along [1 1 0] corresponds to the ground state magnetic moment.