Chirality transfer induced spin selectivity effect in a molecule-metal heterojunction

The chiral geometry of the organic molecule is considered to be crucial to the chiral-induced spin selectivity (CISS) effect. However, the fundamental mechanism responsible for CISS is still debated. In this paper, we propose a mechanism of chirality transfer from chiral molecules to metals by interface coupling in a molecule/metal heterojunction. It is found that the transferred charges present a chiral distribution even in the achiral metal. Using a tight-binding model and tunneling theory, we focus on the induced chiral interface and the strong spin-orbit coupling of the metal, and predict a sizable CISS effect. This work provides a different perspective for us to understand the CISS effect.

Figure 1

Schematic of the side view (a) and the top view (b) of the modeled right-handed helix/metal heterojunction. The red dashed line in (a) indicates the long-range transition between the helical molecule and the metal layers.

Figure 2

Chiral charge density distribution in the metal corresponding to Fig. 1, numbered from (a) the first layer at interface to (f) the sixth layer away from the interface.

Figure 3

(a) Schematic of the scattering region and the electrodes. The dashed line indicates the coupling at the interfaces. (b) Spin-related effective transmission spectrum of the modeled right-handed helix/metal heterojunction, where the area marked by blue shading is enlarged and plotted in (c), and (d) is the corresponding spin polarizations of two enantiomers.

Figure 4

Spin polarization of different (a) coupling strength ${\gamma }_0$ and (b) spin-orbit coupling strength ${\alpha }_0$.

Figure 5

Dependence of spin polarization on helical turns $L$. The black line is the calculated result. The red dots are the experimental data of spin polarization selected from Ref. [7]. The red dashed line is a guide to the eye.