Singlet-Quintet Mixing in Superconductors with j=3/2 Fermions

Recently, a new pairing state with the mixing between s-wave singlet channel and isotropic d-wave quintet channel induced by centrosymmetric spin-orbit coupling has been theoretically proposed in the superconducting materials with j = 3/2 electrons. It is the first realistic proposal of the mixing between different spin channels that preserves the inversion symmetry in solid state systems. As physical consequences, the singlet-quintet pairing mixing can give rise to topological nodal-line superconductivity and surface Majorana flat bands. In this talk, the singlet-quintet-mixed state will be reviewed. Moreover, its experimental signatures, inlcuding spin susceptibility, upper critical field, disorder effect and surface local density of states, will be discussed.