FFLO superconducting state in CeCoIn₅

We present specific heat data for the heavy fermion superconductor CeCoIn₅ close to the upper critical field H _c2 for magnetic fields applied along the [1 0 0] crystallographic axis. For fields above 10 T, the superconducting phase transition becomes first-order. In the same field range, we observe a second specific heat anomaly within the superconducting state, which we attribute to a Fulde–Ferrell–Larkin–Ovchinnikov state.