Double Superconducting Transition of CePt3Si Probed by Susceptibility Measurements

We have investigated ac and dc magnetic susceptibilities (χ ac and χ dc ) of the heavy-fermion superconductor CePt 3 Si ( T c + ∼0.75 K) for two single crystals that show a specific heat anomaly at T c - ∼0.4 K. One crystal shows a double transition at T c + and T c - in the form of structures in the out-of-phase component of χ ac and in χ dc measured in the cooling process. The magnetic field dependence of χ ac suggests that the lower transition also originates in superconductivity. In contrast, only the higher transition has been detected in susceptibility measurements of the other crystal whose specific heat has a less dominant peak near T c - and a broad peak at T c + . These results suggest that CePt 3 Si consists of two superconducting phases with different T c 's, whose volume fraction varies from sample to sample.