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 (C) crossing the saddle point van-Hove singularity. The spin susceptibility in the superconducting state is increased by the topological transitions (A) and (C), while it is decreased by (B). We discuss the unusual magnetic properties observed in Li2Pt3B on the basis of these results.