Chirality-induced spin selectivity and superconducting order parameters

Chirality represents a structure without inversion and mirror symmetries. When electrons pass through chiral molecules, the spin is polarized parallel or antiparallel to the direction of the current, a phenomenon called chirality-induced spin selectivity (CISS) [1]. Recently, it was found that anti-parallel spins accumulate at the ends of superconductor with chiral structure [2]. Although most studies of the CISS focused on normal conductors, the observation of spin accumulation in superconductors, namely CISS in superconductors has attracted much attention.

Superconductivity is characterized by the order parameters, which have structure due to various degrees of freedom of electrons. It is known that the properties of superconductors are strongly affected by the order parameter. Therefore, we study the relationship between CISS and superconducting order parameters. To discuss spin accumulation in superconductors we calculate spin current parallel to the electric current. In particular, we study its dependence on the superconducting order parameters. We find that the current-induced spin current, namely the CISS effect, is significantly enhanced when the spin-singlet and spin-triplet order parameters are hybridized.

[1] B. Göhler et al., Science 331, 894 (2011).

[2] R. Nakajima et al., Nature 613, 479 (2023).