Modulation of electrical conductivity of thin metal films by surface chiral molecule assembly

The effect of chirality-induced spin selectivity (CISS) has attracted extensive interest, notably for its intricate interplay among structural chirality, magnetism, and electron spin/orbitals. In particular, there is evidence that the magnetoconductance of a CISS spin valve – normal metal/chiral molecule/ferromagnet junction - depends on the electronic properties of the normal metal electrode [1]. On the other hand, studies of how assembled surface chiral molecules may affect the electrical transport properties of the thin normal metal films have been scarce. Here, we report a systematic investigation of the effect of self-assembled monolayers (SAMs) of chiral and achiral molecules on the electrical conductivity and carrier density of normal metal thin films. With assembly of chiral molecules on the native oxide surface of Aluminum films up to 15 nm thick, we consistently observed significant increase of the electrical conductivity (up to 66%) with negligible changes in the carrier density. The effect was much smaller when achiral molecules were assembled on the surface. In contrast, on thin films of Gold, the molecules led to slight decreases in electrical conductivity. The observations can be understood as a result of modulation of the spin-dependent scattering rate by the spin-orbit coupling defined by the chiral molecules. The interpretation offers a scattering perspective of the CISS effect, which may provide new insights on the chiral molecule/metal interface considered important in understanding the magnetoconductance of CISS spin valves.

[1] Y. Adhikari, T. Liu, et. al., Nat. Commun. 14:5163 (2023).