Spin-dependent electronic transport is an essential feature not only in engineered devices for spintronics, but also in chemical and biological processes involving the propagation of a current through molecules. In recent years, it has been experimentally verified that an initially unpolarized beam of electrons will emerge polarized (in some cases, significantly) upon traversing a chiral molecule such as a DNA-like helicene; a realization of the so-called chirality-induced spin selectivity (CISS) effect. In the present article we show, based on the use of representation theory within the scattering formalism for transport, that the appearance of such spin polarization is fundamentally allowed in a much wider family of systems, namely those that lack symmetry planes or axes containing the propagation direction. The role of the contacts is hence as qualitatively important as that of the molecules, to the point that the presence of the latter is not generally needed to observe spin polarization. These results are here illustrated by DFT calculations, and can also be extended to the non-equilibrium regime, where the polarization vector is accompanied by a collinear net spin accumulation in the system, which may be detected in magneto-conductance setups.
Spin-dependent transport, and by extension the chirality induced spin selectivity effect, is shown to be fundamentally allowed by the geometry of the system formed by contacts and molecule. We reveal that those supporting spin polarization, may not even need chiral molecules. [Full article]