To address this, researchers at the Institute for Molecular Science (IMS) /SOKENDAI investigated an organic superconductor with chiral symmetry. They focused on nonreciprocity related to spin-orbit coupling and observed an exceptionally large nonreciprocal transport in the superconducting state, far exceeding theoretical predictions. Remarkably, this was found in an organic material with inherently weak spin-orbit coupling, suggesting that chirality significantly enhances charge current-spin coupling with inducing mixed spin-triplet Cooper pairs.

The work is published in the journal Physical Review Research.

Nontrivial spin-current coupling in chirality

In recent years, chiral structures like helical conformations have been revealed to be beyond simple geometric motifs—they have a nontrivial influence on electron transport. A striking manifestation of this phenomenon is the enormous spin polarization termed chirality-induced spin selectivity (CISS), which has been reported extensively in chiral organic molecules.

Conventionally, the efficiency of electron spin polarization during conduction is coupled to the relativistic effect of spin-orbit coupling, a mechanism that becomes stronger with heavier elements. However, since the CISS effect is observed in organic materials composed of light elements such as carbon and hydrogen, this conventional framework falls short, suggesting an unknown coupling between electron motion and spin inherent to chirality.