Unconventional Superconductivity of CePt₃Si Probed by DC Magnetization Measurements

We measured DC magnetization of the noncentrosymmetric superconductor CePt3Si for two single crystals consisting of two superconducting phases with T-c(+) similar to 0.75 K (high-T-c phase) and T-c(-) similar to 0.45 K (low-T-c phase) in different volume fractions. While the magnetic penetration depth derived from the magnetization shows linear temperature dependence in common at low temperatures, indicating a superconducting order parameter with line nodes, the growth of spontaneous magnetizations that appear at T-c(+) and T-c(-) shows complicated temperature dependences depending on the crystallographic direction and the volume fraction of the two phases. The result that the sample with more crystallographic disorders shows larger spontaneous magnetization, together with the fact that the candidates of the superconducting order parameter with line nodes hold time-reversal symmetry, suggests that the spontaneous magnetization is ascribed to the superconductivity at the surface and/or the twin boundary rather than that of the bulk.