Abstract
Organic materials are known to feature long spin-diffusion times, originating in a generally small spin–orbit coupling observed in these systems. From that perspective, chiral molecules acting as efficient spin selectors pose a puzzle that attracted a lot of attention in recent years. Here, we revisit the physical origins of chiral-induced spin selectivity (CISS) and propose a simple analytic minimal model to describe it. The model treats a chiral molecule as an anisotropic wire with molecular dipole moments aligned arbitrarily with respect to the wire’s axes and is therefore quite general. Importantly, it shows that the helical structure of the molecule is not necessary to observe CISS and other chiral nonhelical molecules can also be considered as potential candidates for the CISS effect. We also show that the suggested simple model captures the main characteristics of CISS observed in the experiment, without the need for additional constraints employed in the previous studies. The results pave the way for understanding other related physical phenomena where the CISS effect plays an essential role.
Highlights
The main goal and technological challenge of spintronics is to be able to coherently inject, manipulate, and detect spins in condensed-matter systems.[1]
Besides the original photoelectron transmission through a self-assembled monolayer of chiral molecules,[7] the Chiral-induced spin selectivity (CISS) effect was established by spinspecific conduction through chiral molecules, with gold nanoparticles attached to one end of the molecule,[9,15] as well as by the Hall device measurements, where spin polarization was accompanied by charge redistribution.[16,17]
It is well established that free electron spin−orbit coupling (SOC), α = ħ2/4m2c2, is too small to account for the CISS effect
Summary
The main goal and technological challenge of spintronics is to be able to coherently inject, manipulate, and detect spins in condensed-matter systems.[1]. We are interested in the state of the electron far away from the molecule, so we can approximate the leftmost Green’s function in eq 4 by its well-known asymptotic form, G(r, r′) = −(eikr/4πr) e−iksr, where ks = k(sin θ cos τ, sin θ sin τ, cos θ), and θ and τ denote the polar and azimuthal angles of the scattered electron, respectively. In the current treatment, it is just a mathematical tool to make the second-order scattering analytically tractable, it can be justified physically as a wave packet width of the incoming electron or finite size of the sample. Finite spin polarization can only be obtained considering the scattering up to the second order of perturbation theory
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