Chiral-Induced Spin Selectivity and Non-equilibrium Spin Accumulation in Molecules and Interfaces: A First-Principles Study

Electrons moving through chiral molecules are selected according to their spin orientation and the helicity of the molecule, an effect known as chiral-induced spin selectivity (CISS). The underlying physical mechanism is not yet completely understood. To help elucidate this mechanism, a non-equilibrium Green's function method, combined with a Landauer approach and density functional theory, is applied to carbon helices contacted by gold electrodes, resulting in spin polarization of transmitted electrons. Spin polarization is also observed in the non-equilibrium electronic structure of the junctions. While this spin polarization is small, its sign changes with the direction of the current and with the handedness of the molecule. While these calculations were performed with a pure exchangecorrelation functional, previous studies suggest that computationally more expensive hybrid functionals may lead to considerably larger spin polarization in the electronic structure. Thus, non-equilibrium spin polarization could be a key component in understanding the CISS mechanism.

Automated summary

Electrons moving through chiral molecules are selectively influenced by their spin orientation and the helicity of the molecule in a phenomenon called chiral-induced spin selectivity (CISS). In this study, carbon helices connected to gold electrodes were investigated using a non-equilibrium Green's function method, a Landauer approach, and density functional theory. It was found that the transmitted electrons exhibited spin polarization, which was also observed in the non-equilibrium electronic structure of the junctions. Although the spin polarization was small, its sign changed with the current direction and the handedness of the molecule. The use of computationally more expensive hybrid functionals may lead to larger spin polarization, suggesting that non-equilibrium spin polarization could be a key element in understanding the CISS mechanism.