Angular dependent magnetorestriction study of CeCoIn5

Using a capacitive dilatometer designed to operate on the rotating stage of a top loading dilution refrigerator probe, we measured the magnetorestriction ( L(H)-L(0))/L(0), of the Heavy Fermion Superconductor CeCoIn₅, along all three crystallographic direction, and with the magnetic field applied parallel both to the superconducting ab-planes and to the c-axis. When B||ab, the c-axis magnetorestriction features, besides a sharp jump at the upper critical field, a continuous, second-order like, transition at a lower field, which is consistent with previous observations from specific heat measurements. Our results are consistent with a field induced modulation of the superconducting order parameter (FFLO state), rather than with a field induced magnetic ordering.