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Recently, the spin-selectivity effect of chiral molecules has been attracting extensive and growing interest among the scientific communities. Here, we propose a model Hamiltonian to study spin-dependent electron transport through helicene molecules which are connected by two semi-infinite graphene nanoribbons and try to elucidate a recent experiment of the spin-selectivity effect observed in the helicene molecules. The results indicate that the helicene molecules can present a significant spin-filtering effect in the case of extremely weak spin-orbit coupling, which is three orders of magnitude smaller than the hopping integral. The underlying physics is attributed to intrinsic chiral symmetry of the helicene molecules. When the chirality is switched from the right-handed species to the left-handed species, the spin polarization is reversed exactly. These results are consistent with a recent experiment [V. Kiran et al., Adv. Mater. 28, 1957 (2016)]. In addition, the spin-filtering effect of the helicene molecules is robust against molecular lengths, dephasing strengths, and space position disorder. This theoretical work may motivate further studies on chiral-induced spin selectivity in molecular systems. [ABSTRACT FROM AUTHOR]

Recently, chiral-induced spin selectivity has been attracting intense interest. Here, we report a theoretical study of spin-dependent electron transport in achiral nanotubes contacted by nonmagnetic leads. Our results reveal that by properly connecting to the leads, the achiral nanotubes can present a pronounced spin filtering phenomenon even if the spin-orbit coupling is very weak. In addition, the spin selectivity effect holds for various achiral nanotubes with different radii and is still significant in the presence of strong disorder and dephasing. These findings open new opportunities of using achiral molecules in spintronic applications and could motivate further studies on spin transport along achiral systems. [ABSTRACT FROM AUTHOR]