Unusual behaviours and impurity effects in the noncentrosymmetric superconductor CePt₃Si

We report a study in which the effect of defects/impurities, growth process, off-stoichiometry and presence of impurity phases on the superconducting properties of noncentrosymmetric CePt₃Si is analysed by means of the temperature dependence of the magnetic penetration depth. We found that the linear low-temperature response of the penetration depth—indicative of line nodes in this material—is robust regarding sample quality, in contrast to what is observed in unconventional centrosymmetric superconductors with line nodes. We discuss evidence suggesting that the broadness of the superconducting transition may be intrinsic, though not implying the existence of a second superconducting transition. The superconducting transition temperature systematically occurs at about 0.75 K in our measurements, in agreement with resistivity and ac magnetic susceptibility data but in conflict with specific heat, thermal conductivity and NMR data in which T_c is about 0.5 K. Random defects do not change the linear low-temperature dependence of the penetration depth in the heavy-fermion CePt₃Si with line nodes, as they do in unconventional centrosymmetric superconductors with line nodes.