Spin Susceptibility in Non-centrosymmetric Superconductors with Topological Transition of Fermi Surfaces

The non-centrosymmetric superconductors Li2Pd3B and Li2Pt3B show different superconducting properties despite having the same crystal symmetry. Motivated by experimental results, we investigate the spin susceptibility of non-centrosymmetric superconductors accompanied by the topological transition of Fermi surfaces due to antisymmetric spin-orbit coupling, which is indicated by the first-principles band structure calculation for Li2Pt3B. We study three types of topological transition, namely, (A) the disappearance of the Fermi surface, (B) crossing the Dirac point, and © crossing the saddle point van-Hove singularity. The spin susceptibility in the superconducting state is increased by the topological transitions (A) and ©, while it is decreased by (B). We discuss the unusual magnetic properties observed in Li2Pt3B on the basis of these results.