Non-magnetic impurity and defect doping in superconductors Li ₂Pd₃B with noncentrosymmetric crystal structures

The spin singlet and spin triplet superconducting states can coexist in noncentrosymmetric crystal structures like Li2T3B (T: Pd, Pt), while it is prohibited in ordinary crystal structures. In this study, we focused our research on non-magnetic impurity effect in Li2T3B(T: Pd, Pt). The nature of the pair breaking by non-magnetic impurity in the parity mixing superconducting state is still unclear. We investigated the effect of non-magnetic impurity on s-wave dominant parity mixing superconductor Li2Pd3B by substituting B with Al. In this substitution process, we controlled the quality of the samples and showed their quality deteriorations through the measurement of residual resistivity at Tc. Furthermore, we checked the relations of residual resistivity and Tc as well as its superconducting phase diagram. Our results showed that s-wave dominant parity mixing superconductor Li2Pd3B exhibits the small Tc suppression attributed by the non-magnetic impurities and defects, while the Hc2 value clearly increased about 1.5 times in the poor quality samples. Such behaviours are similarly observed in ordinary s-wave superconductors.