Spin-Dependent Transport in Chiral Molecular Wires

Geometrical chirality is easily noticed for a figure whose image in a mirror cannot be brought to coincidence with itself, nevertheless, the more elusive notion of dynamic chirality has a deeper relevance, as it connects the properties of elementary particles with the observable world. We have investigated the spin-dependent propagation of electrons in helical nanowires and showed that the interplay of spin angular momentum and nanowire chirality, as controlled by the spin-orbit interaction, lifts the symmetry between left and right propagating electrons, thereby giving rise to a chirality induced propagation velocity asymmetry. This study is based on a microscopic tight-binding model that takes into account the spin-orbit interaction. The continuity equation for the spin-dependent probability density is derived, including the spin non-conserving terms, and quantum dynamics calculations are performed to obtain the electron propagating dynamics. The calculations are applied to the first all inorganic double-helix SnIP, a quasi-1D material that constitutes a semiconductor with a bandgap of ~ 1.86 eV. The results have a general validity, nonetheless, due to symmetry considerations and encompass different system realizations. The relation of the propagation velocity asymmetry with the phenomena ascribed to the chiral-induced spin selectivity (CISS) effect is examined, and we propose that the present results can contribute to the understanding of the CISS effect.